Analyte flexure sensor and process for sensing an analyte

Abstract

An analyte flexure sensor provides quantitative measurement of analyte presence or concentration using magnetic signal transduction and can include a flexural member with a primary region that expands or contracts in response to the analyte to a different extent than a secondary region. This differential response creates a bending motion of the flexural member. Magnetic material disposed on the flexural member transduces this motion into a changing magnetic signal. A magnetic field sensitive transducer, positioned proximate to a freely translating region of the flexural member, detects the changing magnetic signal. This signal is received by a readout interface, providing a quantitative measurement of the analyte concentration.

Description

ANALYTE FLEXURE SENSOR AND SENSING AN ANALYTE STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention. CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No.63 / 529,254 (filed July 27, 2023), which is herein incorporated by reference in its entirety. BACKGROUND

[0003] The present invention generally relates to the field of analyte sensors and more particularly to techniques for quantitatively measuring analyte presence or concentration using magnetic signal transduction.

[0004] The field of analyte sensing has seen significant advancements, driven by the need for rapid, accurate, and portable diagnostic tools. Various transduction mechanisms are currently employed, with optics-based modalities that exploit the camera in a cellphone dominating in the field of cheap, portable, accessible sensing systems. However, optics-based analyte sensors face inherent limitations, particularly in optically opaque, scattering, or auto-fluorescing samples. Such samples often necessitate complex pre-processing steps, which can be time-consuming, costly, and require specialized equipment and expertise. Moreover, variable background lighting can also interfere with accurate optical measurements.

[0005] By contrast, magnetics-based sensing offers several advantages, including the ability to perform quantitative measurements directly from opaquesamples, minimal sample preparation, and immunity to auto-fluorescence and light scattering. Yet, despite these advantages, magnetic transduction remains largely underexplored for analyte sensing, particularly for portable, point-of-use applications.

[0006] It is therefore an objective of the present invention to provide a new approach to analyte sensing that exploits the inherent advantages of magnetics-based transduction, thereby overcoming the above-mentioned disadvantages of conventional technologies. Accordingly, methods and equipment for using analyte- responsive magnetic composites to provide portable, inexpensive analyte detection would be advantageous and would be favorably received in the art. BRIEF DESCRIPTION

[0007] Disclosed is analyte flexure sensor. An analyte flexure sensor may be understood as a device that detects the presence or concentration of a specific analyte in a sample. It may be provided that the analyte flexure sensor comprises a flexural member comprising a primary region attached to a secondary region, wherein the primary region is of a material composition that expands or contracts in response to contact with an analyte composition that contains a chosen analyte to a different extent from that of the secondary region. A flexural member can be understood as a structure that bends or deforms in response to an applied force or stimulus. This arrangement provides differential expansion or contraction of the flexural member upon exposure to the analyte, facilitating a measurable mechanical response. One advantage of this is the conversion of modest analyte-induced volume changes into amplified motions, enhancing the sensitivity of the sensor.

[0008] It may be provided that the analyte flexure sensor further comprises magnetic material disposed in or on the flexural member. Magnetic material refers to any substance capable of producing or interacting with a magnetic field. Incorporating magnetic material provides transduction of the flexural member's motion into a changing magnetic field signal, facilitating contactless and optics-free detection.

[0009] It may be provided that the analyte flexure sensor further comprises an analyte composition container for receiving analyte composition and comprising animmobilization member configured to constrain motion of a point, edge, or area of the flexural member while another region of the flexural member translates freely through space. An analyte composition container is a structure for holding the sample containing the analyte. An immobilization member is a component designed to restrict movement of a portion of the flexural member, establishing a fixed reference point or boundary condition. This arrangement ensures that the flexural member's motion is predictable and directed, maximizing the change in magnetic signal with respect to the analyte-induced deformation.

[0010] It may be provided that the analyte flexure sensor further comprises a magnetic field sensitive transducer disposed proximate to the freely translating region of the flexural member in the analyte composition container. A magnetic field sensitive transducer is a device that generates an electrical signal in response to changes in magnetic field strength or other magnetic properties. Positioning the magnetic field sensitive transducer near the moving portion of the flexural member provides it to detect the changing magnetic signal due to analyte-induced deformation, providing a quantitative electronic readout. One advantage of this arrangement is the ability to use a compact, low-cost magnetic field sensitive transducer, such as those commonly found in smartphones.

[0011] It may be provided that the analyte flexure sensor further comprises a readout interface configured to receive an output signal from the magnetic field sensitive transducer that changes in response to translation of the freely translating region of the flexural member. A readout interface is a device for processing, displaying, or communicating the electronic signal from the magnetic field sensitive transducer. One advantage of this is the ability to directly integrate the analyte flexure sensor with existing electronic devices such as smartphones, eliminating the need for additional external electronics or dedicated power sources.

[0012] One aspect of the present invention relates to a process for sensing an analyte. Sensing an analyte may be understood as detecting the presence or measuring the concentration of a specific chemical or biological substance in a sample, or detecting the presence or measuring the amount of a physical property. It may be provided that the process for sensing an analyte comprises contacting a flexural member with an analyte composition that contains an analyte. A flexuralmember can be understood as a structure capable of bending or deforming in response to an applied force or stimulus. An analyte composition refers to the sample that may or may not contain the analyte. This arrangement provides the analyte to interact with the flexural member, triggering a mechanical response proportional to the analyte concentration. One advantage of this approach is its versatility, as flexural members can be designed with tailored material compositions to respond to a wide range of analytes.

[0013] It may be provided that the process for sensing an analyte further comprises detecting a change in a magnetic field proximate to the freely translating second region of the flexural member with a magnetic field sensitive transducer in response to the freely translating second region of the flexural member undergoing translation. A magnetic field refers to the region of influence surrounding a magnet or a moving electric charge. A magnetic field sensitive transducer is a device that generates an electrical signal in response to variations in magnetic field strength or other magnetic properties. This arrangement provides for real-time monitoring of the flexural member’s motion through contactless transduction, simplifying the detection scheme and eliminating the need for optical clarity in the sample.

[0014] It may be provided that the process further comprises receiving an output signal from the magnetic field sensitive transducer in a readout interface. A readout interface is a device or system for processing, displaying, or communicating the electronic signal from the magnetic field sensitive transducer. This arrangement provides the conversion of the magnetic signal changes into a readily interpretable format, such as a numerical display or graphical representation, allowing for convenient and quantitative analyte measurements. One advantage of this approach is the ability to leverage the processing power and display capabilities of readily available electronic devices, such as smartphones, for convenient and user-friendly analyte detection.

[0015] One aspect of the present invention relates to a process for making an analyte flexure sensor. It may be provided that the process for making an analyte flexure sensor comprises providing a flexural member comprising a primary region and a secondary region, wherein the primary region is of a material composition that expands or contracts in response to contact with an analyte composition that containsa chosen analyte to a different extent from that of the secondary region. A flexural member may be understood as a structure capable of bending or deforming in response to an applied force or stimulus. This arrangement provides the creation of a mechanically responsive element that undergoes a predictable and measurable deformation upon interaction with an analyte.

[0016] It may be provided that the process for making an analyte flexure sensor further comprises disposing magnetic material in or on the flexural member. Magnetic material refers to any substance that produces or interacts with a magnetic field. Disposing magnetic material provides for transduction of the mechanical motion of the flexural member into a changing magnetic field, providing a contactless means for detecting analyte-induced deformation. One advantage of this approach is the ability to create a sensor that does not rely on optical transparency of the sample, enabling analysis of opaque liquids.

[0017] It may be provided that the process for making an analyte flexure sensor further comprises disposing the flexural member in an analyte composition container comprising an immobilization member configured to constrain motion of a point, edge, or area of the flexural member. An analyte composition container is a structure designed to hold a sample containing the analyte. An immobilization member can be understood as any component that restricts movement. One advantage of this arrangement is the ability to define a fixed reference point for the flexural member, directing and amplifying its motion in response to analyte-induced deformation. This facilitates accurate and sensitive detection of even small changes in the magnetic field signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following description cannot be considered limiting in any way. Various objectives, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings, in which like reference numerals identify like elements.

[0019] FIG. 1 shows, according to some embodiments, an analyte flexure sensor.

[0020] FIG. 2 shows, according to some embodiments, an analyte flexure sensor.

[0021] FIG. 3 shows, according to some embodiments, an analyte flexure sensor.

[0022] FIG. 4 shows, according to some embodiments, an analyte flexure sensor.

[0023] FIG. 5 shows, according to some embodiments, an analyte flexure sensor.

[0024] FIG. 6 shows, according to some embodiments, an analyte flexure sensor.

[0025] FIG. 7 shows, according to some embodiments, an analyte flexure sensor.

[0026] FIG. 8 shows, according to some embodiments, an analyte flexure sensor.

[0027] FIG. 9 shows, according to some embodiments, an analyte flexure sensor.

[0028] FIG.10 shows, according to some embodiments, an analyte flexure sensor.

[0029] FIG.11 shows, according to some embodiments, an analyte flexure sensor.

[0030] FIG.12 shows, according to some embodiments, an analyte flexure sensor.

[0031] FIG.13 shows, according to some embodiments, an analyte flexure sensor.

[0032] FIG.14 shows, according to some embodiments, an analyte flexure sensor.

[0033] FIG.15 shows, according to some embodiments, an analyte flexure sensor.

[0034] FIG.16 shows, according to some embodiments, an analyte flexure sensor.

[0035] FIG.17 shows, according to some embodiments, an analyte flexure sensor.

[0036] FIG.18 shows, according to some embodiments, an analyte flexure sensor.

[0037] FIG. 19 shows, according to some embodiments, magnetometer- based smartphone sensing. (a) Schematic of full magnetic hydrogel smartphone sensor platform, consisting of an immobilizing clamp, the hydrogel actuator, a phone- attachment piece with a well to hold analyte solution, and a smartphone. (b) Photograph of a prototype sensor platform attached to phone. (c) Schematic of a T- shaped hydrogel actuator, with an inert region along the horizontal length and a bilayer region along the vertical length, consisting of a smart hydrogel (top, yellow) and an inert hydrogel (bottom, grey) with embedded Nd2Fe14B particles. The bilayer region lays flat in the absence of analyte with the Nd2Fe14B particles positioned directly over a magnetometer (left) and curls in the presence of analyte with the Nd2Fe14B particles moved away from the magnetometer, decreasing its observed magnetic field. (d) Photograph of the hydrogel actuator in the absence (left, flat) and presence (right, curled) of the analyte. (e) – (i) Curling of the hydrogel actuator over time, in response to analyte. For clarity, the images show a large degree of curling, though most of the useful signal change occurs for curlings represented in the first few panels.

[0038] FIG.20 shows, according to some embodiments, characterization of magnetometer-based glucose analysis. (a) Actuation of the hydrogel bilayer in 20 mM glucose causes the hydrogel to curve upwards, changing the observed field strength ( ^Bz) of the smartphone magnetometer, which then reverses upon returning to 0 mM glucose. The response is repeatable over three actuation cycles (b), with standarddeviation of the average endpoint magnetometer reading of no more than a half percent of the total response (c). (d) Stepwise additions of glucose over time shows that the platform responds dynamically to glucose concentrations over several orders of magnitude. (d, inset) Measured dose / response calibration curve (connecting dotted line is only to guide the eye).

[0039] FIG.21 shows, according to some embodiments, linear calibration of the glucose and pH sensor platforms. (a) Calibration of the glucose sensor platform, showing the change in observed field strength ^Bzto be approximately linear over two orders of magnitude of glucose concentrations. (b) The change in observed field strength ^Bz of the pH platform is also approximately linear from pH 4 to pH 5. The pH test buffers used were measured in triplicate with a standard benchtop pH meter (standard deviation shown in the horizontal error bars) and plotted against the phone- based measurements, also performed in triplicate (vertical error bars). The negligible size of the vertical error bars on the scale of the plot, suggest that the phone-based measurements are more repeatable than the benchtop pH meter.

[0040] FIG.22 shows, according to some embodiments, detection limit and noise analysis. (a) Average change in smartphone magnetometer reading ( ^Bz) over time for three replicates in response to different glucose concentration levels (labeled), showing that the platform can detect single digit micromolar glucose concentrations. (b) Measurements of the system noise, determined by the standard deviation (S.D.) of the residuals in five different 100-second-long regions, for three different smartphones, each with and without a magnetic hydrogel actuator attached. The noise of the smartphone magnetometer does not increase appreciably when the actuator is added, indicating the noise is dominated by the embedded smartphone magnetometer. (c, left) Increasing the loading of magnetic material in the hydrogel actuator by infusing the Nd2Fe14B particles in PDMS and attaching externally increases ^Bz~10x (c, right) with only a minimal noise penalty. (d) Reducing the distance between the hydrogel actuator and magnetometer from ~ 5 mm closest approach with a phone to ~ 1 mm closest approach with a gauss meter probe, yields a ~50x increase in magnetic field reading.

[0041] FIG. 23 shows, according to some embodiments, smartphone magnetometer analysis of common beverages. (a) The response of the glucoseplatform to various types of wine confirms a higher glucose concentration in the high sugar wine (sangria) than in the dry wines (pinot grigio and champagne brut). The inflection point is due only to an artifact in our measurement setup (see SI). (b) pH testing of orange juice, root beer, and coffee (pH = 4.00, pH = 4.42, and pH = 4.96, respectively, as measured by a pH meter). ^Bzfor each is recorded from a baseline of tap water (pH ~6.5), with the lower pH beverages thus inducing larger ^Bz.

[0042] FIG. 24 shows, according to some embodiments, a magnetic hydrogel smartphone sensor platform. (a) Schematic of the full assembly, including (i) lid, (ii) positioning clamp, (iii) hydrogel actuator, (iv) attachment piece with analyte well, and (v) smartphone. Shims are placed in between the attachment piece and the smartphone on the top and left sides to position the magnetic particles directly over the smartphone magnetometer. (b) Photograph of the assembled magnetometer based smartphone sensor.

[0043] FIG. 25 shows, according to some embodiments, a smartphone attachment piece. Labelled dimensions are in millimeters. Selected dimensions are labelled to give a sense for the overall size of the attachment piece.

[0044] FIG. 26 shows, according to some embodiments, a plastic attachment piece.

[0045] FIG. 27 shows, according to some embodiments, an attachment piece.

[0046] FIG.28 shows, according to some embodiments, control of the initial, analyte-free curvatures of the glucose hydrogel actuators after swelling to equilibrium in pH ൌ 7.4 buffer with 0mM glucose by using inert layers containing (a) 80 ^^L, (b) 70 ^^L, (c) 60 ^^L, (d) 50 ^^L, and (e) 40 ^^L of DMA. Varying the content of DMA in the inert layer compared to the smart hydrogel layer provides the bilayer to lay flat for any chosen initial analyte concentration.

[0047] FIG. 29 shows, according to some embodiments, determination of the magnetometer-based smartphone sensor signal. Raw magnetometer readings (b) collected from 3-axis magnetometer in the (a) background phone, (b) test phone, and (c) the resulting background-subtracted sensor signal. (d) The signal of themagnetometer-based smartphone glucose sensor is generally considered to be the change in field strength of the background-subtracted total field strength^Δ ^^௭^from the 0mM glucose baseline.

[0048] FIG. 30 shows, according to some embodiments, full reversibility data for glucose cycle 1. Several wash cycles are required to fully return the magnetometer-based glucose sensor signal to baseline. The sensor begins in a 0mM glucose solution which is switched to 20mM at time point (1). The solution is returned to 0mM at time point (2) and this 0mM solution is refreshed at timepoints (3) through (9) to account for any residual glucose that might not have been fully washed out during the prior steps.

[0049] FIG. 31 shows, according to some embodiments, magnetometer- based glucose platform signal for the full reversibility test in (a) Cycle 1, (b) Cycle 2, (c) Cycle 3. For each cycle, the sensor reading was recorded in 0mM glucose solution for 1 hour, changed to 20mM glucose for 1 hour, then changed back to 0mM glucose. The 0mM glucose solution must be refreshed several times to return the magnetometer reading to its initial value. Differences in relaxation behavior back to baseline may be due to differences in when, and how thoroughly, wash steps were performed as well as due to potential diffusive mixing of possible remnant glucose in the test well, but once the sensor is back to baseline, it responds again reproducibly to the addition of glucose.

[0050] FIG. 32 shows, according to some embodiments, response time of the same glucose hydrogel actuator to 20mM glucose for (a) Cycle 1, (b) Cycle 2, and (c) Cycle 3.

[0051] FIG.33 shows, according to some embodiments, response of the pH hydrogel actuator between pH4 and pH7 buffers.

[0052] FIG. 34 shows, according to some embodiments, reproducibility of response for the pH sensor platform and phone model comparison. The response ^Δ ^^௭^ of a single pH hydrogel actuator, from pH4 to pH5 buffer, alternating between testing on ( ^^, ^^, ^^^ the Motorola Moto ^^^2020^ and ^ ^^, ^^, ^^^ the Google Pixel 2 over 4days. (g) The response ( Δ ^^௭) of the same pH hydrogel actuator, from a pH4 buffer to a pH 5 buffer, on the Moto E but using the Google Pixel 2 attachment piece.

[0053] FIG. 35 shows, according to some embodiments, pH hydrogel reproducibility. (a) Response of the pH responsive hydrogel actuator on a Motorola Moto E from pH4 to pH5 buffer for three trials (data shown individually in FIGs.34a, c,and e). (b) Response of the pH-responsive hydrogel actuator on a Google Pixel 2 frompH4 buffer to pH5 buffer for three trials (data shown individually in FIGs. 34b, d, andf). (c) Comparison of the 3rdMoto E trial, the 3rdGoogle Pixel 2 trial, and the Moto E response using the Google Pixel 2 attachment piece, showing that the response curve of the Moto E using the Google Pixel 2 attachment matches the response curve of the other Moto E trials rather than the other Google Pixel 2 trials. (d) Average endpoint magnetometer response from pH4 to pH5 buffer on the Moto E, vs the Google Pixel 2.

[0054] FIG.36 shows, according to some embodiments, pH dose / response calibration supporting data for FIG. 21B. Plots show Δ ^^௭over time, with the pH test solution incremented by 0.2pH units periodically, starting at pH4 and ending with pH5 for (a) trial 1, (b) trial 2, and (c) trial 3.

[0055] FIG.37 shows, according to some embodiments, hydrogel actuator response time. (a) The raw magnetometer reading ^ ^^௭^ over time as the test solution is switched from pH4 to pH5 at time ൌ 0 minutes. (b) Normalized response curves showing a clear improvement in the response time with the addition of PEG and with a thinner active layer. (c) Δ ^^௭over time when changing the solution to pH ൌ 4.2,4.8, or 5 from a baseline in pH4 at time ൌ 0 minutes. (d) Δ ^^௭over time showing a clear difference in the signal between pH4.2,4.8, and 5 in the first 30 seconds of response.

[0056] FIG. 38 shows, according to some embodiments, data for the detection limit test (FIG.22a). (a) The average Δ ^^௭over time in response to different glucose concentration levels (labeled), and with error bars showing the range of Δ ^^௭recorded over three replicates for each concentration. (b) Full experimental data collected for detection limit testing, showing the average Δ ^^௭over time in response to five concentrations of glucose. (c) Calibration curve showing the average Δ ^^௭between 119 and 120 minutes in FIG.38b for the five glucose concentrations tested and fit with a linear trend.

[0057] FIG.39 shows, according to some embodiments, data for the noise analysis in FIG. 22b. On three different smartphones of the same model, the magnetometer was recorded for one hour without any sensor platform attached followed by one hour with the sensor platform attachment, with sample data from phone A shown here. (a) The z-direction field strength ^ ^^௭^ as recorded by the magnetometer over the two-hour window, showing ten different 100 -second-long regions where the noise of the system is interrogated, five before and five after the sensor platform attachment is added. (b-k) A linear trend is first fit to the data in each individual region to eliminate to first order any potential long-term background drift and then the noise level (standard deviation of the residuals, SD) is determined based on మthe formula ^^ ^^ ൌ^∑residual^, where ^^ is the number of data points.

[0058] FIG.40 shows, according to some embodiments, evaluation of noise from the dose / response data in FIG.20b. (a) Raw magnetometer data from the sensorphone as the test solution is cycled through 0mM, 10mM,31.6mM, 100mM, 316mM, 1mM, 3.16mM, 10mM, 31.6mM, and 100mM glucose for onehour each. (b-d) Raw magnetometer data from the sensor phone with regions labeled for noise analysis. The regions are 100 seconds long and start 57 minutes after each solution change so that the sensor is closest to equilibrium with the test solution equilibrated. (e) The noise for the region corresponding to each glucose concentration,where SD represents the noise level (standard deviation of the residuals). Since theNdଶFe^ସ B particles move further away from the magnetometer with increasing glucoseconcentration, this data suggests that the noise level is not dependent on proximity of the NdଶFe^ସB particles to the magnetometer and, hence, is unlikely due to any random fluctuations in those particles' field or in their spatial location or orientation as might occur due to vibration or other mechanical disturbances. The data also suggest that the noise is independent of the state of curl of the hydrogel actuator.

[0059] FIG.41 shows, according to some embodiments, bilayer geometry. A flat and curved bilayer of length ^^ and thickness ℎ, is shown sketched in the coordinate system used for all mathematical calculations. The end of the bilayer at the origin of the coordinate system is assumed fixed; the other end is free. The magnetization vector of the magnetized particles (black disk) at the free end of the bilayer strip is shown in red. A magnetometer chip buried below the end of the bilayerstrip at depth ^^^within a cellphone (whose top surface lies at ^^ ൌ 0 ) is also shown. For clarity, the bending angle is exaggerated from what would apply during normal sensor operation.

[0060] FIG.42 shows, according to some embodiments, bilayer curves. Top shows predicted curve taken by a bilayer when one layer of that bilayer changes its length from ^^ to ^^^1 ^ ^^^. Curves shown here are for a bilayer with ^^ ൌ 16 mm and ℎ ൌ 0.65 mm. Bottom overlays predicted bilayer curves onto still-frame images taken from movie S1 of actual bilayer curling (also shown in FIG.19e-19i). As discussed in the text, most of the sensor's useful range already occurs at small angles, but larger bilayer bendings are also included.

[0061] FIG. 43 shows, according to some embodiments, field change Δ ^^௭as a function of hydrogel fractional expansion ^^. Inset overlays a straight line fit, showing degree of linearity over first 50% of sensor dynamic range. Plot is based on equation S16 and shown for a bilayer with ^^ ൌ 20 mm and ℎ ൌ 0.5 mm.

[0062] FIG. 44 shows, according to some embodiments, bilayer versus monolayer sensitivity. For equivalent hydrogel sizes and expansions, and equal magnetizations (arrow), a bilayer moves the embedded magnetic materials (circles) further than a monolayer, resulting in larger field changes and higher sensitivity. Relative sensitivity scalings are shown comparing horizontal and vertical monolayersagainst a bilayer design. Numerical estimates are for a typical bilayer of size ^^ ൌ20 mm, ℎ ൌ 0.5 mm and a magnetometer offset ^^^ ൌ 5 mm. Relative sensitivity of thebilayer system increases further by increasing hydrogel length and / or reducing hydrogel thickness.

[0063] FIG.45 shows, according to some embodiments, an analyte flexure sensor with two immobilization pieces that affix both ends of the flexural member to the test solution container, providing a buckling motion that moves the flexural member away from the magnetic field sensitive transducer.DETAILED DESCRIPTION

[0064] A detailed description of one or more embodiments is presented herein by way of exemplification and not limitation.

[0065] The development of accurate, easy-to-use, and portable analytical tools is rapidly democratizing scientific analysis, making sophisticated laboratory- based testing accessible at significantly reduced costs, with improved convenience, and requiring minimal operator expertise. This paradigm shift is opening doors to decentralized testing, empowering individuals and communities with point-of-use diagnostics, environmental monitoring, and personalized health tracking capabilities. Among the various platforms being explored, such as paper-based diagnostics, wearable sensors, and lab-on-a-chip devices, smartphone-based sensors hold particular promise due to the widespread accessibility of smartphones across the globe, including in resource-limited settings.

[0066] Harnessing the integrated electronics, processing power, and communication capabilities of smartphones offers the potential for more objective, quantitative measurements and data analysis than simpler techniques like paper- based test strips. However, most current smartphone-based sensors rely heavily on optics-based detection, typically using the phone's camera as the primary interface. This limits their applicability in opaque or optically challenging samples and may require additional hardware, increasing cost and complexity. A need exists for an alternative transduction mechanism that can overcome these limitations while retaining the inherent advantages of smartphone integration. Conventional analyte sensors often rely on optical detection methods, requiring transparent samples and complex processing steps. Such sensors may be affected by variable background lighting and struggle with opaque, scattering, or auto-fluorescing samples. Additionally, conventional magnetic sensors typically rely on large magnets or sensitive magnetometers to detect small changes in magnetic field strength, limiting their practicality for portable, point-of-use applications.

[0067] The analyte flexure sensor described herein overcomes these limitations by combining analyte-responsive materials that undergo a programmable, amplified motion with magnetic transduction, enabling sensitive, optics-free detectionin a compact and portable format. It has been discovered that an analyte flexure sensor can be created that is suitable for quantitative measurements of analyte presence or concentration with a simple and inexpensive construction. One advantage of this arrangement is its adaptability to a variety of analytes. The flexural member can be tailored to expand or contract in response to specific target analytes by selecting appropriate material compositions for a primary and secondary region of the analyte flexure sensor. By attaching a primary region and secondary region to a fixed base, differential expansion or contraction occurs in response to analyte contact, generating a measurable mechanical deformation that may result in a translation of the free (non-fixed) end of the flexure sensor that far exceeds any displacement achievable of the free (non-fixed) end of any equivalent analyte sensor that comprises only a uniform material composition without different regions that have different expansion / contraction responses to the analyte under test. This deformation is then transduced into a changing magnetic signal as the magnetic material disposed in or on the flexural member changes its location relative a magnetic field sensor (magnetometer). Since the amount of displacement is related to the amount of analyte, the analyte flexure sensor performs contactless measurements, simplifying the detection scheme and minimizing the need for complex sample preparation. Furthermore, immobilizing one region of the flexural member within an analyte composition container, while allowing another region to translate freely, maximizes the change in the magnetic signal with respect to analyte concentration. This amplified signal, which is due to the displacement amplification enabled by the flexural member comprising at least two regions with different analyte-responsive expansions, can then be detected by a compact and inexpensive magnetic field sensitive transducer, such as those commonly found in smartphones, enabling portable, point-of-use applications. The output signal from the magnetic field sensitive transducer is then readily processed and displayed by the readout interface. In the case of a smartphone this provides a quantitative measure of analyte concentration without requiring dedicated electronics or an external power source.

[0068] In an embodiment, an analyte flexure sensor (100) includes a flexural member (101) comprising a primary region (102) attached to a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with an analyte composition (108) that contains an analyte to adifferent extent from that of secondary region (103), magnetic material (104) disposed in or on flexural member (101), an analyte composition container (109) for receiving analyte composition (108) and comprising an immobilization member (110) that constrains motion of a point, edge, or area of flexural member (101) while another region of flexural member (101) translates freely through space, a magnetic field sensitive transducer (105) disposed proximate to the freely translating region of flexural member (101) in analyte composition container (109), wherein magnetic field sensitive transducer (105) produces an output signal that changes in response to translation of the freely translating region of flexural member (101), and a readout interface (106) configured to receive the output signal from magnetic field sensitive transducer (105). In an embodiment, the analyte flexure sensor (100) includes primary region (102) that expands or contracts in response to contact with the analyte composition (108) and secondary region (103) that does not. In an embodiment, the analyte flexure sensor (100) includes the flexural member (101) that comprises a bilayer structure, wherein primary region (102) is a first layer and secondary region (103) is a second layer of the bilayer structure. In an embodiment, the analyte flexure sensor (100) includes the first layer and the second layer that are attached by covalent bonding. In an embodiment, the analyte flexure sensor (100) includes at least one of the first layer or the second layer that comprises a hydrogel. In an embodiment, the analyte flexure sensor (100) includes primary region (102) and secondary region (103) that are integral and comprise a gradient in material composition extending from primary region (102) to secondary region (103). In an embodiment, the analyte flexure sensor (100) includes the magnetic material (104) that is disposed in the freely translating region of flexural member (101). In an embodiment, the analyte flexure sensor (100) includes the magnetic material (104) that includes a plurality of magnetic particles embedded in flexural member (101). In an embodiment, the analyte flexure sensor (100) includes the magnetic field sensitive transducer (105) that includes a magnetometer. In an embodiment, the analyte flexure sensor (100) includes the readout interface (106) that includes a smartphone.

[0069] The analyte flexure sensor (100) is a novel apparatus that offers a new approach to analyte detection by combining the sensitivity of analyte-responsive materials with the simplicity and versatility of magnetic transduction. The flexural member (101) is a mechanically responsive element that deforms in a predictablemanner upon interaction with the analyte. The flexural member (101) comprises a primary region (102) and a secondary region (103) joined together. The primary region (102) is fabricated from a material that exhibits a specific expansion or contraction in response to the analyte, while the secondary region (103) exhibits a different degree of expansion or contraction under the same conditions. This differential response generates a bending motion in the flexural member (101), proportionally amplifying the initial analyte-induced volume change. This amplified motion facilitates sensitive detection, even for analytes that induce modest material expansion or contraction.

[0070] The magnetic material (104) is disposed in or on the flexural member (101), enabling transduction of the mechanical deformation into a changing magnetic signal. The magnetic material (104) can take various forms, including embedded magnetic particles, a thin magnetic film, or an attached magnetic element. As the flexural member (101) bends in response to analyte presence, the position of the magnetic material (104) shifts relative to a fixed point, resulting in a measurable change in magnetic field strength or direction.

[0071] An analyte composition container (109) is employed to contain the analyte composition (108) and to provide structural support for the flexural member (101). An immobilization member (110) within the analyte composition container (109) constrains the motion of a specific point, edge, or area of the flexural member (101), establishing a fixed reference point for its deformation. This immobilization can be achieved through various means, such as a mechanical clamp, an adhesive bond, or a slot within the container. By restricting motion at a specific point, the immobilization member (110) ensures that the flexural member (101) deforms predictably and that the movement of the magnetic material (104) is maximized.

[0072] In an embodiment, the flexural member can function as the analyte composition container with the analyte composition deposited directly onto the flexural member which then contains the analyte composition due to the geometry of the flexural member and / or its ability to partially or wholly absorb the analyte composition .

[0073] In an embodiment, the analyte composition container is the surface (without any surrounding walls) on which the flexural member is placed, the analytecomposition being contained by its own adhesive forces to the surface and its own cohesive surface tension forces.

[0074] A magnetic field sensitive transducer (105) is positioned proximate to the freely translating region of the flexural member (101) within the analyte composition container (109). The magnetic field sensitive transducer (105) is a device that converts changes in magnetic field strength or other magnetic properties into an electronic signal. Examples of suitable transducers include Hall effect sensors, magnetoresistive sensors, Gauss meters or other magnetometers. Other possible magnetometers include NMR or MRI machines. In these cases, the flexural member (102) may be placed inside the magnetic field detector. The close proximity of the magnetic field sensitive transducer (105) to the magnetic material (104) provides it to detect even small changes in the magnetic field caused by the flexural member’s (101) movement. This arrangement provides contactless and label-free detection of the analyte, eliminating the need for complex optical or electrochemical setups.

[0075] A readout interface (106) receives the output signal from the magnetic field sensitive transducer (105). The readout interface (106) can take various forms, ranging from a simple analog meter to a sophisticated digital processor integrated with a display. It processes the electronic signal from the magnetic field sensitive transducer (105), enabling quantitative measurement of the analyte concentration. This information can then be displayed, recorded, or transmitted for analysis and interpretation. One advantage of this approach is the ability to leverage existing electronic devices, such as smartphones, for convenient and user-friendly analyte detection.

[0076] This analyte flexure sensor (100) achieves several technical advantages through the specific implementation of its components. The flexural member (101) is designed to amplify small analyte-induced volume changes, enhancing sensitivity. The use of magnetic material (104) provides for contactless detection, simplifying the sensor design and enabling analysis of opaque samples. Immobilizing one region of the flexural member (101) with the immobilization member (110) further increases sensitivity by maximizing the movement of the magnetic material (104) in response to analyte presence. Employing a compact, low-cost magnetic field sensitive transducer (105) provides portability and integration withexisting electronic devices like smartphones. The readout interface (106) processes and displays the electronic signal, providing a user-friendly and quantitative measurement of analyte concentration.

[0077] In one embodiment of the analyte flexure sensor (100), the primary region (102) expands or contracts in response to contact with the analyte composition (108), while the secondary region (103) does not. This arrangement, where one region is analyte-responsive and the other is dimensionally inert, enhances the bending motion of the flexural member (101), resulting in greater sensitivity. The flexural member (101) can be implemented as a bilayer structure, with the primary region (102) forming a first layer and the secondary region (103) forming a second layer. The first layer and second layer may be attached through various methods, including covalent bonding, adhesive bonding, or physical entanglement. Covalent bonding, in particular, offers a strong and stable attachment between the layers, ensuring consistent and reliable performance. At least one of the layers in the bilayer structure can comprise a hydrogel, a three-dimensional network of crosslinked polymers that can absorb and retain significant amounts of water. Hydrogels are well-suited for analyte sensing applications due to their biocompatibility, tunable mechanical properties, and ability to incorporate specific chemical functionalities for analyte recognition. The magnetic material (104) may be comprised of a plurality of magnetic particles embedded within the flexural member (101). This arrangement provides for the magnetic material (104) to move seamlessly with the flexural member (101) as it bends, ensuring a consistent and accurate transduction of the mechanical deformation into a magnetic signal. The magnetic particles can be permanently magnetized, superparamagnetic, or ferromagnetic, offering flexibility in sensor design and sensitivity. In certain embodiments, the system includes a bias magnetic field produced, e.g., by magnets not attached to the flexural member that can magnetize the magnetic material disposed in or on the flexural member, or that offsets the total field recorded by the magnetometer. A magnetometer serves as a suitable magnetic field sensitive transducer (105) for detecting the changing magnetic field generated by the moving magnetic material (104). Magnetometers are readily available, compact, and inexpensive, making them well-suited for integration into portable devices. Finally, a smartphone can function as the readout interface (106), receiving the output signalfrom the magnetometer and enabling convenient display, processing, and communication of the analyte measurement.

[0078] This specific implementation of the analyte flexure sensor achieves numerous technical advantages. The bilayer structure of the flexural member (101) with a responsive primary region (102) and a non-responsive secondary region (103) creates a highly sensitive element for converting analyte-induced volume changes into amplified motions. The covalent bonding between the layers ensures structural integrity and reliability. Using a hydrogel as one of the layers provides biocompatibility, tunability, and analyte specificity. Embedding magnetic particles within the flexural member (101) provides seamless transduction of the mechanical motion into a changing magnetic signal. The use of a magnetometer as the transducer (105) offers compactness, low cost, and sensitivity. Integrating the sensor with a smartphone as the readout interface (106) provides for portable, user-friendly analyte detection, leveraging existing technology for convenient measurement and data processing.

[0079] As an alternative to a bilayer structure, the flexural member (101) can be fabricated with the primary region (102) and secondary region (103) integrated as a single element. Instead of distinct layers, a gradient in material composition can be engineered to extend from the primary region (102) to the secondary region (103). This gradient can be achieved through various techniques, such as varying the concentration of crosslinking agents within a hydrogel, creating a gradual transition in pore size, or using a blend of materials with differing analyte responsiveness. This arrangement facilitates a smooth and continuous bending motion in response to analyte contact. One advantage of this design is the potential for higher mechanical robustness and durability compared to a bilayer structure.

[0080] For modifying sensitivity, it is beneficial to position the magnetic material (104) solely within or on the freely translating region of the flexural member (101). This ensures that the movement of the magnetic material (104) is directly coupled to the maximum deformation induced by the analyte, maximizing the change in the magnetic signal.

[0081] The immobilization member (110) can direct the flexural member’s (101) motion and thus maximize signal change. In an embodiment, the immobilizationmember (110) constrains motion at one end of the flexural member (101), creating a cantilever-like configuration. This can be achieved with a simple mechanical clamp or by embedding one end of the flexural member (101) within a slot or channel in the analyte composition container (109).

[0082] The use of a gradient material composition in the flexural member (101) offers the potential for increased mechanical robustness. Strategically positioning the magnetic material (104) within the freely translating region maximizes signal change and thus sensitivity. Constraining motion at one end of the flexural member (101) with the immobilization member (110) creates a predictable bending motion, enhancing the accuracy and sensitivity of the sensor.

[0083] In an embodiment, the analyte flexure sensor (100) is a novel device for detecting and quantifying the presence or concentration of the analyte in a sample. The analyte flexure sensor (100) operates based on the principle of magnetic transduction, leveraging the measurable changes in magnetic field strength or direction caused by analyte-induced deformation of a flexural member. This approach offers distinct advantages over conventional optical detection methods, particularly in opaque, scattering, or auto-fluorescing samples. It eliminates the need for complex pre-processing steps and is immune to interference from variable background lighting. The analyte flexure sensor (100) comprises a mechanically responsive element coupled to magnetic material, enabling contactless and label-free detection. Its sensitivity can be further enhanced by strategically immobilizing one region of the flexural member, maximizing the movement of the magnetic material in response to analyte presence. The sensor can be integrated with simple and inexpensive magnetic field transducers, such as those found in smartphones, making it suitable for portable, point-of-use applications.

[0084] In an embodiment, the flexural member (101) is a mechanically responsive element that undergoes a predictable and measurable deformation upon interaction with a target analyte. This deformation is then transduced into a changing magnetic signal, enabling analyte detection. The flexural member (101) can be implemented using various materials and configurations. One approach is to utilize a bilayer structure, comprising two distinct layers with different material properties. The primary region (102) of the bilayer is fabricated from a material that exhibits a specificexpansion or contraction in response to the chosen analyte, while the secondary region (103) exhibits a different degree of expansion or contraction. This differential response generates a bending motion in the flexural member (101) that is proportional to the analyte concentration. Alternatively, the flexural member (101) can be fabricated as a single element with a gradient in material composition extending from the primary region (102) to the secondary region (103). This gradient can be created by varying the concentration of crosslinking agents within a hydrogel or by using a mixture of materials with differing analyte responsiveness. This configuration provides for a smooth and continuous bending motion, potentially enhancing the sensor's robustness and simplifying fabrication. The shape of the flexural member (101) can be a rectangular strip. It also can be tapered, curved, or patterned to optimize sensitivity, response time, and mechanical properties. Examples include T-shapes, cantilevers, and structures with notches or hinges. The material composition of the flexural member (101) can be tailored to target specific analytes. Hydrogels are well- suited for this purpose due to their biocompatibility, tunable mechanical properties, and ability to incorporate specific chemical functionalities for analyte recognition.

[0085] In an embodiment, the primary region (102) forms the analyte- responsive region of the flexural member (101). It is fabricated from a material that undergoes a specific expansion or contraction in response to the presence of the chosen analyte. This responsiveness can be achieved through various mechanisms, such as chemical binding, electrostatic interactions, or changes in osmotic pressure. For example, a hydrogel comprising boronic acid groups can be used as the primary region (102) for glucose sensing. Boronic acid binds to glucose, causing the hydrogel to shrink, resulting in a measurable bending motion. The degree of responsiveness can be tailored by adjusting the concentration of the analyte-sensitive component within the material. The choice of material for the primary region (102) depends on the target analyte and the desired sensitivity. Various polymers, hydrogels, and composite materials can be employed. In addition to chemical modifications, the primary region (102) can be engineered with specific structural features, such as patterned surfaces or microchannels, to further enhance its responsiveness and sensitivity.

[0086] In an embodiment, the secondary region (103) serves as the reference region of the flexural member (101). It is fabricated from a material that exhibits a different degree of expansion or contraction compared to the primary region (102) when exposed to the analyte composition. Ideally, the secondary region (103) is dimensionally inert, meaning it does not change size in response to the chosen analyte. This inertness enhances the bending motion of the flexural member (101), as the differential response between the primary and secondary regions (102 and 103) is maximized. The secondary region (103) can be implemented using various materials, including inert hydrogels, polymers, or even thin, flexible sheets of metal or plastic or paper. The choice of material depends on factors such as the desired stiffness, compatibility with the primary region (102), and fabrication method.

[0087] In an embodiment, the magnetic material (104) is integrated into the flexural member (101) to provide transduction of the mechanical deformation into a changing magnetic signal. As the flexural member (101) bends in response to analyte presence, the position of the magnetic material (104) shifts, altering the magnetic field strength or direction at a nearby magnetic field sensor. The magnetic material (104) can be implemented in various forms, including embedded magnetic particles, a thin magnetic film, or an attached magnetic element. The choice of implementation depends on factors like sensitivity, cost, and fabrication method. Embedding magnetic particles within the flexural member (101) offers seamless integration and provides for precise control over the position and distribution of the magnetic material. A thin magnetic film can be deposited onto the surface of the flexural member (101), providing a uniform magnetic field. Attaching a separate magnetic element, such as a small magnet, offers the advantage of easy replacement or adjustment. The magnetic properties of the magnetic material (104) can be tailored to optimize the sensor's sensitivity and dynamic range.

[0088] In an embodiment, the magnetic field sensitive transducer (105) detects the changing magnetic field generated by the moving magnetic material (104). This transducer (105) converts changes in magnetic field strength or direction into an electronic signal, enabling quantitative measurement of the analyte concentration. Various types of magnetic field sensitive transducers (105) can be employed, including magnetometers, Hall effect sensors, and magnetoresistive sensors. The choice oftransducer (105) depends on factors like sensitivity, cost, and size. Magnetometers, particularly those found in smartphones, are compact, inexpensive, and offer sufficient sensitivity for many analyte detection applications. Hall effect sensors are simple and robust, while magnetoresistive sensors provide high sensitivity.

[0089] In an embodiment, the readout interface (106) receives the output signal from the magnetic field sensitive transducer (105) and processes it to provide a measurement of the analyte concentration. The readout interface (106) can be integrated with the transducer (105) or can be a separate device, such as a smartphone or computer. The readout interface (106) can be implemented using various technologies, including microcontrollers, single-board computers, and application-specific integrated circuits. It can perform various functions, including signal amplification, filtering, calibration, and data display. The choice of readout interface (106) depends on the desired functionality, complexity, and cost of the sensor.

[0090] In an embodiment, flexural motion (107) refers to the bending or deformation of the flexural member (101) in response to contact with the analyte composition (108). This motion is proportional to the analyte concentration and is responsible for causing the change in the magnetic signal that is detected by the magnetic field sensitive transducer (105). The specific direction and magnitude of flexural motion (107) depends on the design of the flexural member (101), the properties of the chosen analyte, and the immobilization configuration.

[0091] In an embodiment, the analyte composition (108) refers to the sample being analyzed for the presence or concentration of a specific analyte. It can be a liquid, a gas, or a solid, as long as it can be brought into contact with the flexural member (101) and induce a measurable deformation. The composition of the analyte sample (108) can vary widely depending on the application. It can be a biological fluid like blood, serum, or urine; an environmental sample like water or air; or even a food or beverage product.

[0092] In an embodiment, the analyte composition container (109) is a structure designed to hold the analyte composition (108) and to provide support for the flexural member (101). It can be implemented as a well, a reservoir, a chamber,or any other suitable container that can accommodate the sample volume and is compatible with the analyte composition (108). The size and shape of the analyte composition container (109) can be tailored to suit different applications, ranging from microfluidic devices for analyzing small volumes to larger containers for bulk sample analysis. The material of the container (109) can be chosen based on its chemical compatibility with the analyte composition (108) and the desired sensor lifetime.

[0093] In an embodiment, the immobilization member (110) is an optional component of the analyte flexure sensor (100) that serves to restrict motion of a point, edge, or area of the flexural member (101). This immobilization directs the bending motion of the flexural member (101) and maximizes the change in the magnetic signal in response to analyte presence. The immobilization member (110) can be implemented in various forms, such as a mechanical clamp, a slot within the analyte composition container (109), or an adhesive bond. The choice of immobilization method can be determined based on factors such as the desired level of stability, ease of assembly, and manufacturing cost. In an embodiment, the immobilization member (110) secures the flexural member (101) within the analyte composition container (109), ensuring a consistent and controlled bending motion. The specific implementation of the immobilization member (110) can vary depending on the design of the flexural member (101) and the analyte composition container (109). Some examples of immobilization members include a mechanical clamp, slot, and adhesive bond. The mechanical clamp can be a simple spring-loaded clip, a screw clamp, or a more sophisticated mechanism that applies pressure to hold the flexural member (101) in a fixed position. The clamp can be made from various materials, such as plastic, metal, or ceramic, and its design can ensure secure attachment without damaging the flexural member. The slot or channel can be incorporated into the analyte composition container (109), providing a space for the flexural member (101) to be inserted and immobilized. The dimensions and shape of the slot can be customized to accommodate various configurations of the flexural member (101). This approach is advantageous for integration with existing devices, such as smartphones, where the slot can be designed to align the flexural member (101) with the internal magnetic field sensor. In an adhesive bond, an adhesive, such as glue or epoxy, can be used to attach the flexural member (101) to the analyte composition container (109). This method offers a strong and permanent bond and can be beneficial for applicationsrequiring high stability and durability. The choice of adhesive can be based on its compatibility with the materials of the flexural member (101) and the analyte composition container (109), as well as the operating conditions of the sensor. The immobilization member (110) is an optional component of the analyte flexure sensor (100). Immobilization can also be achieved directly through the design of the analyte composition container (109), such as by using a tapered or constricted region to secure one end of the flexural member (101). The choice of immobilization method (110) depends on factors such as the desired level of stability, ease of assembly, cost, and the specific requirements of the application. The goal is to provide a stable and predictable bending motion while minimizing any interference with the movement of the magnetic material (104).

[0094] In an embodiment, with reference to FIG. 1, the analyte flexure sensor (100) is shown in a configuration where the flexural member (101) is a bilayer structure, immobilized at one end within an analyte composition container (109). The flexural member (101) is shown in both a flat, non-actuated state (dashed outline) and a bent, actuated state (solid outline). The flexural member (101) comprises a primary region (102) and a secondary region (103) joined together. In this embodiment, the primary region (102) shrinks in response to contact with an analyte composition (108) containing the chosen analyte to a greater extent than the secondary region (103). This differential shrinkage induces a bending motion (107) in the flexural member (101). The magnetic material (104) is disposed near the free end of the flexural member (101), which is a free end that is not immobilized. As the flexural member (101) bends, the magnetic material (104) moves, changing the magnetic field strength at the magnetic field sensitive transducer (105). The readout interface (106) then processes and displays the signal from the transducer (105), providing a measurement of the analyte concentration. The analyte composition container (109) holds the analyte composition (108) and can be made of a material compatible with the analyte, such as plastic or glass. The immobilization member (110) can be implemented as a clamp, a slot, or an adhesive bond, ensuring a secure attachment of the flexural member (101) to the analyte composition container (109). The magnetic field sensitive transducer (105) is positioned proximate to the magnetic material (104) in the analyte composition container (109) to provide for sensitive detection of the magnetic field changes. The readout interface (106) can be integrated with the magnetic fieldsensitive transducer (105) or can be a separate device, such as a smartphone or a computer. This embodiment highlights operation of the analyte flexure sensor (100), where the analyte-induced deformation of the flexural member (101) is translated into a change in the magnetic field that is detected by a magnetic field sensitive transducer (105). The flexibility in the design of the flexural member (101), the choice of materials, and the arrangement of the components provide for adaptation of the sensor to various analytes and detection environments.

[0095] In an embodiment, with reference to FIG. 2, the analyte flexure sensor (100) is shown with the primary region (102) expanding in response to the analyte composition (108), resulting in the flexural member (101) bending away from the magnetic field sensitive transducer (105). This configuration demonstrates the interchangeability of the primary region (102) and secondary region (103). In some embodiments, the primary region (102) was shown on the top of the flexural member (101) and shrinking in response to the analyte. In this embodiment, the primary region (102) is on the bottom of the flexural member (101) and expands in response to the analyte. This change in orientation, with the responsive member on the bottom, does not fundamentally alter the operation of the sensor. The flexural member (101) still bends in response to the analyte, causing the magnetic material (104) to move relative to the transducer (105). The immobilization member (110) secures the flexural member (101) to the analyte composition container (109) and provides for controlled and directional bending. The analyte composition container (109) holds the analyte composition (108) and can be made from various materials, such as plastic, glass, or ceramic. The magnetic material (104) can be embedded in the flexural member (101) or attached to its surface, and its size and shape can be varied to optimize sensitivity. The magnetic field sensitive transducer (105) can be positioned below the flexural member (101), above it, or even to the side, as long as it is positioned proximate to the magnetic material (104) to detect changes in the magnetic field. The readout interface (106) can be a separate device that receives the output signal from the magnetic field sensitive transducer (105) or can be integrated with the transducer itself. This embodiment highlights the adaptable nature of the analyte flexure sensor (100), demonstrating that the relative positions of the primary and secondary regions (102 and 103) can be interchanged without altering the fundamental operatingprinciple of the sensor. This design flexibility provides for optimization of the sensor for specific applications and detection requirements.

[0096] In an embodiment, with reference to FIG. 3, the magnetic field sensitive transducer (105) is shown as a separate component from the readout interface (106). The flexural member (101) is shown immobilized at one end within the analyte composition container (109). Upon contact with analyte composition (108), the flexural member (101) bends, causing the magnetic material (104) to move, changing the magnetic field strength at the magnetic field sensitive transducer (105). The readout interface (106) receives a signal from the magnetic field sensitive transducer (105) and displays information related to the analyte presence or concentration. The magnetic field sensitive transducer (105) is positioned proximate to the magnetic material (104) within the analyte composition container (109). The readout interface (106) can be positioned near the container (109) or located remotely. A wired or wireless connection can be used to transmit the signal from the magnetic field sensitive transducer (105) to the readout interface (106). In some embodiments, the magnetic field sensitive transducer (105) and the readout interface (106) are separate components. Alternatively, the magnetic field sensitive transducer (105) and readout interface (106) can be integrated into a single unit, simplifying the design and potentially reducing the overall size and cost of the analyte flexure sensor (100). This integration is advantageous for implementing the sensor with a smartphone, where the phone's internal magnetometer serves as the magnetic field sensitive transducer (105) and the phone's processor and display screen serve as the readout interface (106). The flexural member (101) can be implemented as a bilayer or gradient structure, and the analyte composition container (109) can be adapted to suit various form factors and sample volumes. This embodiment highlights the flexibility in the arrangement of the components of the analyte flexure sensor (100), allowing for optimization based on specific application requirements.

[0097] In an embodiment, with reference to FIG. 4, the analyte flexure sensor (100) is shown in two configurations, both without an analyte composition container (109). In the top portion of the figure, the flexural member (101) is immobilized at one end by an immobilization member (110), and the analyte composition (108) is disposed directly onto the flexural member (101). Thisconfiguration provides for direct contact between the analyte composition (108) and the primary region (102) of the flexural member (101), potentially enhancing sensitivity and reducing response time. In the bottom portion of the figure, the analyte flexure sensor (100) is shown without an analyte composition container (109) or an immobilization member (110). The analyte composition (108) is disposed as a drop that covers the flexural member (101) and a portion of the readout interface (106). This configuration is advantageous for situations where minimal sample volume is available or when direct contact with the readout interface (106) is not detrimental. In both configurations, the magnetic field sensitive transducer (105) is positioned proximate to the flexural member (101) to detect changes in the magnetic field (104) as the flexural member (101) bends in response to the analyte composition (108). The readout interface (106) receives the output signal from the magnetic field sensitive transducer (105) and provides a measurement of the analyte presence or concentration. Although not shown in this figure, it may be desirable to include a thin, flat layer of material between the flexural member (101) and the readout interface (106) to protect the readout interface (106) from coming into contact with the analyte composition (108). This protective layer could be made of a material that is impermeable to the analyte composition (108), such as a hydrophobic polymer. The omission of the analyte composition container (109) in these embodiments simplifies the design of the analyte flexure sensor (100) and reduces its overall size, making it particularly suitable for applications where miniaturization and portability are paramount. These alternative configurations demonstrate the versatility and adaptability of the analyte flexure sensor (100) for a wide range of sample types, volumes, and detection environments.

[0098] In an embodiment, with reference to FIG. 5, the magnetic material (104) is shown disposed in the top layer (102) of the flexural member (101), which in this embodiment is a bilayer structure. The magnetic material (104) is in the form of a plurality of magnetic particles embedded within the top layer (102). As the flexural member (101) bends in response to the analyte composition (108) in the analyte composition container (109), the magnetic particles move along with the top layer (102), causing a change in the magnetic field that is detected by the magnetic field sensitive transducer (105). The readout interface (106) receives the signal from the transducer (105) and provides a measurement of the analyte concentration. Thisembodiment demonstrates that the magnetic material (104) can be embedded in the top layer of a bilayer flexural member (101). Alternatively, the magnetic particles could be embedded in the bottom layer (103) of the bilayer. The choice of layer for embedding the magnetic material (104) can be determined based on the specific design requirements of the sensor, such as the direction of bending or the desired sensitivity. Furthermore, the magnetic material (104) is not limited to being embedded within a specific layer. The magnetic particles could be located in both layers of the bilayer or could be distributed throughout the flexural member (101). The magnetic particles can also be fashioned into any shape with any density of particles, providing flexibility in the design of the magnetic component of the analyte flexure sensor (100). For example, the magnetic particles could be arranged in a line, a circle, or a more complex pattern. The density of the magnetic particles can be varied to adjust the strength of the magnetic field generated. One advantage of embedding the magnetic material (104) within the flexural member (101) is that it provides for a seamless integration of the magnetic and mechanical components of the sensor. This can improve the sensitivity and accuracy of the sensor by ensuring that the movement of the magnetic material (104) is directly coupled to the deformation of the flexural member (101).

[0099] In an embodiment, with reference to FIG. 6, the magnetic material (104) is shown as a block of magnetic material attached externally to the flexural member (101). This configuration demonstrates an alternative implementation of the magnetic component of the analyte flexure sensor (100). The flexural member (101) is shown immobilized at one end within the analyte composition container (109). As the flexural member (101) bends in response to the analyte composition (108), the attached magnetic block (104) moves with it. This movement changes the magnetic field strength at the magnetic field sensitive transducer (105), enabling detection of the analyte. The magnetic block (104) can be attached to the side of the flexural member (101), as shown in the figure, or it could be attached above or below the flexural member (101). The choice of attachment location can be determined based on the desired direction of movement of the magnetic block (104) and the location of the magnetic field sensitive transducer (105). The magnetic block (104) could also be embedded within the flexural member (101), similar to the embedded magnetic particles shown in previous embodiments. The shape, size, and magnetic propertiesof the magnetic block (104) can be varied to optimize the sensitivity and response time of the sensor. For example, a larger magnetic block (104) may generate a stronger magnetic field, while a smaller one may be more suitable for integration into compact devices. The magnetic field sensitive transducer (105) can be a magnetometer, a Hall effect sensor, or any other suitable device that can detect changes in magnetic field strength. The readout interface (106) processes the signal from the magnetic field sensitive transducer (105) to provide a quantitative measurement of the analyte concentration. This embodiment highlights the versatility in implementing the magnetic material (104) within the analyte flexure sensor (100). The use of an externally attached magnetic block (104) can simplify fabrication and provide for easier replacement or adjustment of the magnetic component, if needed.

[0100] In an embodiment, with reference to FIG. 7, the flexural member (101) is shown as a single element comprising a gradient in material composition. This embodiment demonstrates an alternative to a bilayer structure for achieving differential expansion or contraction in response to the analyte. The flexural member (101) includes a primary region (102) at the top and a secondary region (103) at the bottom. The primary region (102) is designed to be more responsive to the chosen analyte compared to the secondary region (103). The gradient in material composition extends from the top to the bottom of the flexural member (101), creating a continuous transition in analyte responsiveness. The magnetic material (104) is disposed near the free end of the flexural member (101). When the flexural member (101) is exposed to an analyte composition (108), the primary region (102) at the top expands or contracts to a greater extent than the secondary region (103) at the bottom. This differential response induces a bending motion (107) in the flexural member (101), causing the magnetic material (104) to move relative to the magnetic field sensitive transducer (105). The gradient in material composition can be achieved by various methods, such as by varying the concentration of crosslinking agents in a hydrogel or by using a mixture of materials with different analyte responsiveness. For example, a hydrogel could be synthesized with a higher concentration of crosslinking agents in the primary region (102) and a lower concentration in the secondary region (103). This would result in a gradient in stiffness, with the primary region (102) being stiffer than the secondary region (103). This gradient in stiffness would cause the flexural member (101) to bend more in the region of higher stiffness (the primary region (102)) upon exposure to theanalyte. Alternatively, a mixture of two different hydrogel materials could be used, one that is highly responsive to the analyte and one that is inert. The ratio of these two materials could be varied along the length of the flexural member (101) to create a gradient in analyte responsiveness. This arrangement eliminates the need for distinct layers in the flexural member (101), potentially increasing its mechanical robustness and simplifying fabrication. The gradient-based design offers another means to achieve a sensitive and responsive analyte flexure sensor (100) by taking advantage of tailored material properties to control and amplify the bending motion.

[0101] In an embodiment, with reference to FIG. 8, the secondary region (103) of the flexural member (101) is made entirely from the magnetic material (104). This embodiment demonstrates an alternative approach to integrating the magnetic component into the flexural member (101). The flexural member (101) is immobilized at one end by the immobilization member (110) within the analyte composition container (109). The primary region (102) is attached to the top of the secondary region (103), which is now also the magnetic material (104). When the flexural member (101) is exposed to an analyte composition (108), the primary region (102) expands or contracts, causing the flexural member (101) to bend. As the flexural member (101) bends, the secondary region (103), which is the magnetic material (104), moves relative to the magnetic field sensitive transducer (105). This motion results in a change in the magnetic field detected by the transducer (105), providing a signal that corresponds to the analyte concentration. This configuration offers advantages in terms of simplifying the fabrication process. It eliminates the need to separately embed or attach magnetic material (104) to the flexural member (101). The secondary region (103) can be implemented as an agglomeration of magnetic particles or as a single, solid, but flexible, thin magnet. The choice of implementation can be determined based on the desired sensitivity, flexibility, and cost of the sensor. The magnetic field sensitive transducer (105) can be positioned below, above, or to the side of the flexural member (101), depending on the direction of bending and the desired detection range. This embodiment highlights the potential for incorporating the magnetic material (104) as a structural component of the flexural member (101), potentially improving the sensitivity and robustness of the analyte flexure sensor (100).

[0102] In an embodiment, with reference to FIG.9, various configurations of the immobilization member (110) are shown for securing the flexural member (101) within the analyte composition container (109). The immobilization member (110) constrains a portion of the flexural member (101) from movement to provide a controlled and directional bending motion. One embodiment of the immobilization member (110) is a clamp that secures the flexural member (101) from above. This clamp can be a simple mechanical device, such as a spring-loaded clip or a screw clamp that applies pressure to hold the flexural member (101) in place. Another embodiment of the immobilization member (110) is a slot that is integrated into the analyte composition container (109). The flexural member (101) can be inserted into the slot, which constrains its motion along one or more axes. The dimensions and shape of the slot can be customized to accommodate various configurations of the flexural member (101). A third embodiment of the immobilization member (110) uses an adhesive, such as glue or epoxy, to secure the flexural member (101) to the analyte composition container (109). This approach provides a strong bond and can be advantageous for ensuring long-term stability and durability. The choice of immobilization method can be determined based on the specific application requirements, such as the desired level of stability, ease of assembly, and cost considerations. The immobilization member (110) is an optional component of the analyte flexure sensor (100). The embodiment can be practiced without an immobilization member (110), and immobilization can be achieved directly through the design of the analyte composition container (109). For example, if the walls of the analyte composition container (109) are made narrow at one end, they can squeeze and trap one end of the flexural member (101), providing sufficient immobilization for the sensor to function. These alternative configurations for the immobilization member (110) highlight the flexibility and adaptability of the analyte flexure sensor (100) for various fabrication methods and design constraints.

[0103] In an embodiment, with reference to FIG. 10, multiple flexural members (101) and multiple magnetic field sensitive transducers (105) may be combined in an analyte flexure sensor (100). FIG. 10 shows a plan view of the arrangement. Each flexural member (101) can be responsive to a different analyte, enabling the detection of multiple analytes with a single device. Alternatively, multiple flexural members (101) could be made responsive to the same analyte. Thisconfiguration can enhance the sensor’s sensitivity to that particular analyte by increasing the overall signal change. Each flexural member (101) can be contained in the same analyte composition container (109) or each could be contained within a separate container. Sharing the same analyte composition container (109) can simplify the design and reduce the overall size of the sensor. Using separate analyte composition containers (109) offers advantages in terms of modularity and preventing cross-contamination between samples. Each separate flexural member (101) can be associated with a dedicated magnetic field sensitive transducer (105) positioned beneath the magnetic material (104). This arrangement ensures that the magnetic signal change from each flexural member (101) is independently measured, maximizing sensitivity and accuracy for each analyte. All the flexural members (101) within the device can share the same readout interface (106), simplifying the processing and display of the multiple analyte measurements. The readout interface (106) can be implemented as a smartphone, a single-board computer, or a dedicated processing unit with a display. This multiplexed configuration provides simultaneous sensing of a variety of analytes or offers enhanced sensitivity for a single analyte.

[0104] In an embodiment, with reference to FIG. 11, the analyte flexure sensor (100) can include multiple flexural members (101) and a single, multi-axis magnetic field sensitive transducer (105). This arrangement provides for multiplexed detection of multiple analytes using a single transducer. Each flexural member (101) includes magnetic material (104) magnetized in a different direction. For example, one flexural member (101) can include magnetic material (104) magnetized in the x- direction, another in the y-direction, and another in the z-direction. This directional magnetization provides the magnetic field sensitive transducer (105) to differentiate between the signals from each flexural member (101) based on the direction of the magnetic field change. The multiple flexural members (101) can be responsive to different analytes, enabling simultaneous detection of multiple analytes in a single sample or in separate samples. Alternatively, the multiple flexural members (101) could be responsive to the same analyte. This configuration can increase the overall signal change and thus enhance the sensitivity of the sensor for that particular analyte. The multiple flexural members (101) could be integrated into a single analyte composition container (109), simplifying the design and reducing the overall size of the sensor. Alternatively, each flexural member (101) could be housed in a separateanalyte composition container (109), providing modularity and preventing cross- contamination between samples. The readout interface (106) receives the signals from the magnetic field sensitive transducer (105) and processes them to determine the concentration of each analyte based on the magnitude and direction of the magnetic field change. This embodiment highlights the potential for miniaturization and increased complexity of the analyte flexure sensor (100) by utilizing multi-axis magnetic field sensitive transducers (105) and directional magnetization to provide multiplexed analyte detection.

[0105] In an embodiment, with reference to FIG. 12, the analyte flexure sensor (100) can include multiple flexural members (101), each disposed in a different orientation, and a single, multi-axis magnetic field sensitive transducer (105). This embodiment demonstrates a configuration where the magnetic material (104) is magnetized in the same direction for each of the flexural members (101). The magnetic field sensitive transducer (105) is capable of measuring changes in magnetic field strength in multiple directions, enabling differentiation between signals generated by each flexural member (101) based on the direction of movement of the magnetic material (104). For example, one flexural member (101) is responsive to analyte 1 and responds preferentially in the x-direction. This flexural member (101) would be disposed such that its longest dimension extends along the y-axis, and it is constrained from motion at one end by an immobilization member (110). Another flexural member (101) is responsive to analyte 2 and responds preferentially in the z-direction, which in FIG.12 is out of the page. This flexural member (101) would be disposed upright, such that its longest dimension extends along the x-direction , with its bottom end constrained by an immobilization member (110). Another flexural member (101) is responsive to analyte 3 and responds preferentially in the negative y-direction. This flexural member (101) would be disposed such that its longest dimension extends along the x or z-axis and is constrained at one end by an immobilization member (110). In this embodiment, all three flexural members (101) are arranged such that their respective freely translating ends with the magnetic material (104) are positioned over the magnetic field sensitive transducer (105). As each flexural member (101) bends in response to its respective analyte, the magnetic material (104) moves either towards or away from the magnetic field sensitive transducer (105), generating a change in the magnetic field that is detected by the multi-axis sensor. The readoutinterface (106), which could be a smartphone, then receives the signals from the magnetic field sensitive transducer (105) and processes them to determine the concentration of each analyte based on the magnitude and direction of the magnetic field change. Each of the three flexural members (101) could be integrated into the same analyte composition container (109) or each could be housed in separate containers, depending on the specific application requirements. This embodiment demonstrates the versatility of the analyte flexure sensor (100) for multiplexed detection of multiple analytes by strategically arranging flexural members (101) with directional responsiveness and utilizing a single multi-axis magnetic field sensitive transducer (105).

[0106] In an embodiment, with reference to FIG. 13, the flexural member (101) is shown in a T-shape. The flexural member (101) comprises a primary region (102) attached to a secondary region (103). The magnetic material (104) is disposed on the flexural member (101). The top portion of the T-shape can provide a surface area for immobilization with an immobilization member (110). This arrangement provides the bottom portion of the T-shaped flexural member (101) to translate freely through space. The T-shape is just one possible shape for the flexural member (101). It can take numerous other forms including rectangular, square, circular, or triangular shapes. The flexural member (101) can also be tapered, wherein one end is wider than the other. This can be advantageous for directing the bending motion towards a specific region of the sensor. The edges of the flexural member (101) can be rounded to reduce stress concentrations and improve durability. The relative size and shape of the primary region (102) and secondary region (103) can also be varied. For example, the primary region (102) can be thicker or thinner than the secondary region (103), or it can be longer or shorter. These variations can be used to tune the sensitivity and response time of the sensor. The magnetic material (104) can be positioned at various locations on the flexural member (101), either embedded within the structure or attached to its surface. A T-shaped flexural member (101) can be particularly advantageous for smartphone integration. The top portion of the T-shape can be immobilized within a slot or channel of a phone attachment, while the bottom portion extends downwards towards the smartphone's internal magnetometer. This configuration provides for a compact and efficient sensor design, leveraging the existing capabilities of the smartphone. The flexibility in shape, size, and materialcomposition of the flexural member (101), as well as the positioning of the magnetic material (104), highlights the adaptability of the analyte flexure sensor (100) for a wide range of applications and detection scenarios.

[0107] In an embodiment, with reference to FIG. 14, the flexural member (101) is shown in two alternative shapes. One embodiment of the flexural member (101) is tapered, wherein one end is wider than the other. The taper provides for controlled and localized bending of the flexural member (101) in response to the analyte composition (108). This shape can be advantageous for concentrating the motion of the magnetic material (104) near the magnetic field sensitive transducer (105), thereby enhancing the sensitivity of the sensor. Another embodiment of the flexural member (101) includes a patterned surface. This pattern can take various forms, such as vertical or diagonal ribs, or other shapes or textures. A patterned surface can be used to enhance the responsiveness of the flexural member (101) by increasing its surface area or by introducing local variations in stiffness. This can lead to a more pronounced bending motion and thus a stronger magnetic signal change upon contact with the analyte. The pattern can be incorporated into either the primary region (102) or the secondary region (103) or both. The primary region (102) and secondary region (103) do not need to be the same geometry. They can have different lengths, widths, thicknesses, and shapes. This flexibility in design provides for optimization of the flexural member (101) for specific applications and target analytes. For example, a longer, thinner flexural member (101) may be more sensitive to small changes in analyte concentration, while a shorter, thicker one may be more robust and durable. The choice of pattern, shape, and dimensions can be tailored to achieve the desired sensitivity, response time, and mechanical properties for the analyte flexure sensor (100). These alternative shapes and surface patterns demonstrate the versatility of the flexural member (101) and its adaptability for diverse analyte sensing applications.

[0108] In an embodiment, with reference to FIG. 15, the analyte flexure sensor (100) is integrated with a smartphone (106) to provide a portable and user- friendly detection system. The flexural member (101) is implemented as a bilayer hydrogel structure in a T-shape. The top, horizontal section of the T-shape is comprised solely of the secondary region (103), which is an inert hydrogel, providinga surface for immobilization. The bottom, vertical arm of the hydrogel is a bilayer with the primary region (102) on top and the secondary region (103) on the bottom. The primary region (102) is a hydrogel that shrinks in response to the analyte, such as glucose. The magnetic material (104) is embedded within the bilayer section of the flexural member (101). This T-shaped flexural member (101) is secured within an analyte composition container (109) that is part of an attachment and alignment device (111). This device (111) is designed to align the flexural member (101) with the smartphone's internal magnetometer (105), which serves as the magnetic field sensitive transducer (105). The immobilization member (110) secures the horizontal section of the T-shaped flexural member (101) within the device (111), allowing the vertical arm to bend freely in response to the analyte. Upon contact with the analyte, the vertical arm of the flexural member (101) bends upwards, moving the magnetic material (104) away from the smartphone's magnetometer (105). This change in distance alters the magnetic field strength detected by the magnetometer (105), generating an output signal that corresponds to the analyte concentration. The smartphone (106) then displays the measured magnetic field value on its screen, providing a direct and user-friendly readout. The attachment and alignment device (111) could be implemented as a 3D printed or molded plastic structure that securely attaches to the smartphone. The analyte composition container (109) could be a well or reservoir within the device (111) that holds the analyte composition (108). This embodiment demonstrates a practical implementation of the analyte flexure sensor (100) as a portable and accessible detection system by leveraging the existing capabilities of smartphones, including their integrated magnetometers (104) and display screens (106).

[0109] In an embodiment, with reference to FIG. 16, the flexural member (101) of the analyte flexure sensor (100) is shown in a trilayer configuration. The flexural member (101) comprises a primary region (102), a secondary region (103), and the magnetic material (104). In this embodiment, the primary region (102) is divided into two separate sections, one on the top and one on the bottom of the flexural member (101), with the secondary region (103) located in between. Both sections of the primary region (102) are of the same material that responds to the chosen analyte. The magnetic material (104) is disposed at one end of the flexural member (101). When the flexural member (101) is initially fabricated, it can be formed as a straightelement. A notch is formed in the secondary region (103), separating the two sections of the primary region (102). This notch serves as a hinge that provides a localized bending motion in response to the analyte. When the flexural member (101) is contacted with an analyte composition (108), the primary region (102) expands or contracts, causing the hinge to bend, resulting in flexural motion (107). This motion can be in either direction, depending on whether the primary region (102) expands or contracts. As the hinge bends, the magnetic material (104) at the end of the flexural member (101) moves relative to the magnetic field sensitive transducer (105), which produces a signal change. This arrangement facilitates sensitive detection by concentrating the bending motion at the hinge. The size and shape of the notch can be varied to tune the sensitivity and response time of the sensor. For example, a smaller notch may result in a more sensitive but slower response, while a larger notch may result in a less sensitive but faster response. The trilayer structure with a hinge offers greater design flexibility compared to a simple bilayer configuration. It provides for a wider range of motion and provides a more localized and controlled deformation, potentially enhancing the sensitivity and accuracy of the analyte flexure sensor.

[0110] In an embodiment, with reference to FIG. 17, the flexural member (101) of the analyte flexure sensor (100) includes three flexural members, a primary region (102), a secondary region (103), and a tertiary region (112). This arrangement demonstrates the potential for multiple bending motions within a single flexural member (101) to create a more complex movement. The primary region (102) is designed to be responsive to a first analyte, and the tertiary region (112) is designed to be responsive to a second analyte. The secondary region (103) is an inert layer. The magnetic material (104) is disposed on the end of the tertiary region (112). In this embodiment, the primary flexural member (102) and tertiary region (112) are each subdivided into two sections that are separated by the inert secondary region (103), forming two separate bilayer sections. The first bilayer section is located at the end of the flexural member (101) that is immobilized by the immobilization member (110). The second bilayer section is located at the freely translating end of the flexural member (101) that includes the magnetic material (104). Each bilayer section forms a hinge that bends in response to its respective analyte. When the flexural member (101) is exposed to an analyte composition (108) containing the first analyte, the primary region (102) expands or contracts, causing the first hinge to bend and initiatingflexural motion (107). This bending can reorient the second bilayer section relative to the magnetic field sensitive transducer (105). When the flexural member (101) is also exposed to the second analyte, the tertiary region(112) expands or contracts, causing the second hinge to bend, further contributing to flexural motion (107) and changing the position of the magnetic material (104) relative to the magnetic field sensitive transducer (105). This arrangement provides a complex movement of the magnetic material (104) in response to the presence of two different analytes. The embodiment is not limited to having two hinges, and could have three or more hinges, allowing for even greater control and complexity in the flexural member's (101) motion. The additional flexural members could be responsive to different analytes or to the same analyte, but with varying degrees of responsiveness. This flexibility provides for tailored design of the flexural member (101) to achieve specific detection goals. The use of multiple hinges within a single flexural member (101) offers the potential to program unique and complex motion patterns, enabling a wide range of sensing capabilities.

[0111] In an embodiment, with reference to FIG. 18, the flexural member (101) can be engineered to exhibit a twisting motion in response to the analyte composition (108). This twisting motion can be achieved through specific design features of the flexural member (101), such as patterning the primary region (102) with diagonal stripes. FIG.18 shows a top-down view of two different arrangements of the diagonal stripes. In one arrangement, the diagonal stripes of the primary region (102) are spaced apart, creating gaps where the secondary region (103) is exposed. In another arrangement, the diagonal stripes of the primary region (102) are closer together, with minimal or no gaps between them. The diagonal stripes are oriented such that they exert a selective force on the flexural member (101) when the primary region (102) expands or contracts. This force induces a twisting motion (107) about the longitudinal axis of the flexural member (101). The magnetic material (104) is disposed at the free end of the flexural member (101), which is opposite the end constrained by the immobilization member (110). As the flexural member (101) twists, the magnetic material (104) rotates, changing the direction of its magnetic field rather than just its distance from the magnetic field sensitive transducer (105). This change in magnetic field direction can be detected by a multi-axis magnetic field sensitive transducer (105), allowing for sensitive measurement of the analyte concentration.The twisting motion offers several potential advantages for analyte sensing. It can provide a more distinct change in the magnetic field compared to simple bending, enabling higher sensitivity. The twisting motion also provides for a larger range of movement with minimal overall displacement, which can be beneficial for integration into compact devices. Furthermore, the degree of twist can be amplified by increasing the length of the flexural member (101) or by optimizing the geometry and spacing of the diagonal stripes in the primary region (102). This twisting mechanism demonstrates the versatility of the analyte flexure sensor (100) and its ability to achieve a variety of motion patterns for sensitive and versatile analyte detection.

[0112] In an embodiment, with reference to FIG. 45, the analyte flexure sensor is shown with two immobilization pieces (110) which affix both ends of the flexural member (101) to the test solution container (110), resulting in a buckling motion that moves the flexural member (101) away from the magnetic field sensitive transducer (105). The analyte flexure sensor (100) is shown with the primary region (102) expanding in response to the analyte composition (108), resulting in the flexural member (101) buckling the magnetic material (104) away from the magnetic field sensitive transducer (105). The immobilization members (110) secure the flexural member (101) to the analyte composition container (109) and provides for controlled and directional buckling. The analyte composition container (109) holds the analyte composition (108) and can be made from various materials, such as plastic, glass, or ceramic. The magnetic material (104) can be embedded in the flexural member (101) or attached to its surface, and its size and shape can be varied to optimize sensitivity. The magnetic field sensitive transducer (105) can be positioned below the flexural member (101), above it, or even to the side, as long as it is positioned proximate to the magnetic material (104) to detect changes in the magnetic field. The readout interface (106) can be a separate device that receives the output signal from the magnetic field sensitive transducer (105) or can be integrated with the transducer itself. This embodiment could provide enhanced stability for the sensor for specific applications and detection requirements. The buckling mechanism demonstrates the versatility of the analyte flexure sensor (100) and its ability to achieve a variety of motion patterns for sensitive and versatile analyte detection.

[0113] The analyte flexure sensor leverages the unique properties of stimuli- responsive hydrogels to provide a sensitive, quantitative, and optics-free method for measuring analyte concentrations in liquid samples. In an embodiment, the analyte flexure sensor comprises a specially designed hydrogel actuator, or test strip, that acts as the mechanically responsive element. This hydrogel actuator can be fabricated in a bilayer configuration, where two distinct hydrogel layers are bonded together. The top layer is a smart hydrogel that undergoes a predictable and measurable volume change in response to the target analyte. This responsiveness can be tailored to various analytes by incorporating specific chemical functionalities into the hydrogel network, such as boronic acid groups for glucose sensing or acrylic acid groups for pH sensing. The bottom layer is an inert hydrogel that does not respond to the analyte, serving as a reference layer and enhancing the bending motion of the bilayer structure.

[0114] Embedded within the hydrogel actuator, typically near its free end, is a carefully positioned ensemble of permanently magnetized microparticles. These particles, often comprised of neodymium iron boron for their strong magnetic properties, are coated with silica to prevent corrosion and ensure stability in aqueous environments. The hydrogel actuator is initially designed to lay flat in the absence of the analyte, positioning the magnetized particles at a defined distance from a magnetic field sensitive transducer. Upon exposure to the target analyte, the smart hydrogel layer expands or contracts, causing the bilayer structure to bend or curl. This motion displaces the magnetic particles relative to the transducer, altering the magnetic field strength or direction. The transducer, such as a magnetometer, then converts this change in magnetic field into an electronic signal, providing a quantitative readout of the analyte concentration.

[0115] In an embodiment, the analyte flexure sensor is designed for the sensitive and quantitative detection of glucose, a crucial analyte in medical diagnostics, bioprocessing, and food analysis. This embodiment leverages the unique properties of boronic acid-based hydrogels, which exhibit a reversible volume change in response to glucose concentration, coupled with the simplicity and accessibility of smartphone-based magnetic transduction.

[0116] The analyte flexure sensor can include a T-shaped hydrogel actuator comprising an inert region and a bilayer region. The inert region, formed along thehorizontal axis of the T, provides a stable platform for immobilizing the actuator within a sample container. The bilayer region, extending along the vertical axis of the T, comprises the sensing and actuating element. This bilayer is fabricated using two distinct hydrogels: an inert hydrogel on the bottom and a glucose-responsive smart hydrogel on the top.

[0117] The inert hydrogel is synthesized from acrylamide, a common monomer for creating hydrogels, crosslinked with N,N'-methylenebisacrylamide (BIS) to form a three-dimensional network. The concentration of BIS determines the stiffness and swelling properties of the hydrogel. A small amount of N-(3- dimethylaminopropyl acrylamide) (DMA) is also incorporated into the inert hydrogel formulation. DMA introduces a positive charge into the hydrogel network, influencing its swelling behavior and enabling fine-tuning of the initial bilayer curvature.

[0118] The glucose-responsive smart hydrogel is synthesized using a similar formulation, but with the addition of 3-(acrylamido)phenylboronic acid (3-APB). 3-APB serves as the glucose recognition element, as its boronic acid group reversibly binds to the cis-diol groups present in glucose. Upon binding, the hydrogel network undergoes a decrease in negative charge and an increase in crosslinking density, leading to a decrease in swelling volume.

[0119] Both hydrogel layers are formed through a controlled photopolymerization process. The hydrogel precursor solutions, containing monomers, crosslinkers, and a photoinitiator, are dispensed into a T-shaped mold fabricated from polydimethylsiloxane (PDMS). The bottom, inert layer is partially cured under UV light, creating a semi-solid structure. Then, silica-coated neodymium iron boron (Nd2Fe14B) microparticles are mixed with additional inert hydrogel precursor and deposited onto the partially cured layer. A small permanent magnet placed beneath the mold attracts the magnetic particles, concentrating them into a disk- shaped ensemble near the bottom tip of the T-shape, before the inert layer is fully cured. This entraps the magnetic particles within the inert hydrogel layer, forming the magnetic component of the sensor. Finally, the glucose-responsive smart hydrogel precursor is deposited on top of the cured inert layer and exposed to UV light for complete polymerization and bonding, forming the bilayer structure.

[0120] The fabricated T-shaped hydrogel actuator is then immobilized within a sample container, typically a small well or reservoir attached to a smartphone. The inert horizontal section of the T is secured using a clamp or an adhesive bond, ensuring that the bilayer region extends downwards towards the phone's surface. A drop of the analyte solution, containing glucose, is then introduced into the sample container, allowing it to come into contact with the bilayer region of the hydrogel actuator.

[0121] The smartphone's internal magnetometer, located near its surface, serves as the magnetic field sensitive transducer. In the absence of glucose, the bilayer region of the hydrogel actuator lays flat, positioning the embedded magnetic particles directly above the magnetometer. This creates a baseline magnetic field reading. As glucose diffuses into the smart hydrogel layer, the 3-APB groups bind to glucose, causing the smart layer to shrink. This differential shrinkage between the top and bottom layers induces an upward bending motion in the bilayer, moving the magnetic particles away from the magnetometer.

[0122] The magnetometer detects this change in magnetic field strength, generating an electronic signal that is proportional to the degree of bending and thus to the glucose concentration. The smartphone's internal processor then converts this signal into a numerical value, leveraging prior calibration data to provide a quantitative measurement of the glucose level. This measurement is displayed on the smartphone's screen, offering a user-friendly and readily interpretable readout.

[0123] This embodiment of the analyte flexure sensor provides a sensitive, low-cost, and portable analyte detection system by combining tailored hydrogel materials with the ubiquitous capabilities of smartphones. The boronic acid-based hydrogel bilayer provides a highly specific and responsive element for glucose detection. The integration of magnetic transduction with the smartphone's internal magnetometer and processing power provides a compact, user-friendly, and quantitative detection platform that requires no additional hardware or external power sources.

[0124] In an embodiment, a process for sensing an analyte with an analyte flexure sensor (100) includes: contacting a flexural member (101) with an analytecomposition (108) that contains an analyte, the flexural member (101) comprising a primary region (102) attached to a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with the analyte composition (108) to a different extent from that of secondary region (103), and further wherein the flexural member (101) has a first region that is constrained from motion and a second region that translates freely through space, detecting a change in a magnetic field (104) proximate to the freely translating second region of flexural member (101) with a magnetic field sensitive transducer (105) in response to the freely translating second region of flexural member (101) undergoing translation, and receiving an output signal from the magnetic field sensitive transducer (105) in a readout interface (106). In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes the change in the magnetic field (104) that is a decrease in magnetic field strength. In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes determining a concentration of the chosen analyte in the analyte composition (108) based on the output signal from the magnetic field sensitive transducer (105). In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes the determining that comprises correlating the output signal with a concentration of the chosen analyte based on prior calibration of the analyte flexure sensor (100). In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes primary region (102) that expands or contracts in response to contact with the analyte composition (108) and secondary region (103) that does not. In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes the flexural member (101) that comprises a bilayer structure, wherein primary region (102) is a first layer and secondary region (103) is a second layer of the bilayer structure. In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes the first layer and the second layer that are attached by covalent bonding. In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes at least one of the first layer or the second layer that comprises a hydrogel. In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes primary region (102) and secondary region (103) that are integral and comprise a gradient in material composition extending from primary region (102) to secondary region (103). In an embodiment, the process for sensing an analyte with an analyte flexure sensor (100) includes the contacting that comprisesdisposing the flexural member (101) in an analyte composition container (109), and further wherein an immobilization member (110) in the analyte composition container (109) constrains the flexural member (101) from motion at the first region.

[0125] The process for sensing an analyte using the analyte flexure sensor (100) involves a series of steps that leverage the mechanical response of the flexural member (101) and the sensitivity of magnetic transduction. The process begins with contacting the flexural member (101) with an analyte composition (108) that contains the chosen analyte. The flexural member (101), comprising a primary region (102) and a secondary region (103), is designed to bend or deform in a predictable manner upon interaction with the analyte. The primary region (102) is fabricated from a material that expands or contracts in response to the chosen analyte, while the secondary region (103) exhibits a different degree of response. This differential response generates a bending motion in the flexural member (101), effectively amplifying the initial analyte- induced volume change. The flexural member (101) is immobilized at a first region, creating a fixed point for the bending motion. A second region of the flexural member (101) translates freely through space, allowing for maximum displacement. This controlled and amplified movement of the flexural member (101) forms the basis for analyte detection.

[0126] The next step in the process involves detecting the change in a magnetic field (104) proximate to the freely translating second region of the flexural member (101) with a magnetic field sensitive transducer (105). The magnetic field (104) is generated by the magnetic material (104) that is disposed in or on the flexural member (101). As the flexural member (101) bends in response to the analyte, the magnetic material (104) moves relative to the magnetic field sensitive transducer (105), causing a change in magnetic field strength or direction. This change is detected by the transducer (105), generating an electronic signal that corresponds to the magnitude of the bending motion, which is directly related to the analyte concentration.

[0127] The next step in the process is receiving the output signal from the magnetic field sensitive transducer (105) in a readout interface (106). The readout interface (106) processes the electronic signal, converting it into a readable format for the user. This can involve various operations such as signal amplification, filtering,calibration, and conversion to a digital value. The readout interface (106) can then display the measured analyte concentration, store it for later analysis, or transmit it to another device.

[0128] This process for sensing an analyte leverages the sensitivity of analyte-responsive materials, the simplicity of magnetic transduction, and the processing capabilities of electronic readout interfaces. By contacting the flexural member (101) with the analyte composition (108), a measurable mechanical deformation is produced. The movement of the magnetic material (104) within the flexural member (101) generates a change in magnetic field (104), detected by the transducer (105). This change is converted to an electronic signal and processed by the readout interface (106) to provide a quantitative measure of analyte concentration. This approach provides sensitive, optics-free detection, eliminates the need for complex sample preparation, and offers the potential for miniaturization and integration with readily available devices like smartphones.

[0129] In one embodiment, the change in the magnetic field (104) is a decrease in magnetic field strength, which occurs as the magnetic material (104) moves away from the magnetic field sensitive transducer (105) due to the bending of the flexural member (101). This configuration is particularly advantageous when the initial position of the magnetic material (104) is close to the transducer (105), maximizing the relative change in field strength. The process can also include determining the concentration of the analyte in the analyte composition (108) based on the output signal from the magnetic field sensitive transducer (105). This determination can be achieved by correlating the output signal with a concentration of the chosen analyte based on prior calibration of the analyte flexure sensor (100). Calibration involves exposing the sensor to known concentrations of the analyte and recording the corresponding output signals. The resulting data can be used to create a calibration curve or a look-up table that provides for direct conversion of the measured signal into an analyte concentration.

[0130] The primary region (102) of the flexural member (101) may expand or contract in response to the analyte, while the secondary region (103) remains unaffected. This arrangement, where one region is analyte-responsive and the other is inert, enhances the bending motion, leading to a greater change in the magneticfield and thus higher sensitivity. The flexural member (101) may be implemented as a bilayer structure, with the primary region (102) as a first layer and the secondary region (103) as a second layer. These layers can be attached through various methods, including covalent bonding, which offers a strong and stable connection. At least one of the layers may be made of a hydrogel, providing biocompatibility and tunability. The contacting of the flexural member (101) with the analyte composition (108) may be achieved by disposing the flexural member (101) within an analyte composition container (109). This container (109) holds the analyte solution and typically includes an immobilization member (110) to constrain the flexural member (101) from motion at a specific point or region.

[0131] Measuring a decrease in magnetic field strength offers high sensitivity when the magnetic material (104) starts near the transducer (105). Determining the analyte concentration by correlating the output signal with a calibration curve provides quantitative measurements. Using a bilayer structure with an analyte-responsive primary region (102) and an inert secondary region (103) maximizes bending and enhances sensitivity. Covalently bonding the layers ensures stability and reliability. Employing a hydrogel as one of the layers provides biocompatibility and tunability. Disposing the flexural member (101) within an analyte composition container (109) with an immobilization member (110) facilitates controlled and directional bending, further improving sensitivity and accuracy.

[0132] To perform analyte sensing using the analyte flexure sensor (100), the first step involves preparing the sensor for interaction with the sample. The flexural member (101), comprising a primary region (102) and a secondary region (103), is carefully positioned within the analyte composition container (109). The immobilization member (110) within the container (109) secures a specific point or region of the flexural member (101), ensuring a controlled and directional bending motion. The magnetic material (104) incorporated into the flexural member (101) is situated in close proximity to the magnetic field sensitive transducer (105), maximizing the sensor's sensitivity to changes in the magnetic field. Once the sensor is properly arranged, the analyte composition (108) containing the chosen analyte is introduced into the analyte composition container (109). The analyte molecules then interact with the primary region (102) of the flexural member (101), causing it to expand or contract.This expansion or contraction occurs to a different extent than in the secondary region (103), leading to a bending motion in the flexural member (101). The extent of bending is proportional to the concentration of the analyte in the sample. As the flexural member (101) bends, the magnetic material (104) embedded within or attached to it moves relative to the magnetic field sensitive transducer (105). This movement alters the magnetic field strength or direction at the transducer (105), generating an electronic signal. The magnitude of this signal change corresponds to the degree of bending in the flexural member (101) and, consequently, to the concentration of the analyte in the sample.

[0133] The electronic signal from the magnetic field sensitive transducer (105) is then transmitted to the readout interface (106). The readout interface (106) may perform various signal processing operations, such as amplification, filtering, and conversion to a digital format. Based on prior calibration of the sensor with known analyte concentrations, the readout interface (106) converts the measured signal into a quantitative value representing the analyte concentration in the sample. This value is then displayed on the readout interface (106), enabling the user to interpret the results. The process of analyte sensing using the analyte flexure sensor (100) can be further refined and optimized through specific implementations of the claim elements. In one embodiment, the change in the magnetic field (104) detected by the magnetic field sensitive transducer (105) is a decrease in magnetic field strength. This decrease occurs when the bending motion of the flexural member (101) moves the magnetic material (104) further away from the transducer (105). This configuration is particularly advantageous when the initial position of the magnetic material (104) is close to the transducer (105), maximizing the relative change in signal and thus the sensitivity. To achieve quantitative measurement of the analyte concentration, the process may include determining the concentration based on the output signal from the magnetic field sensitive transducer (105). This determination is accomplished by correlating the output signal with a known concentration of the analyte based on prior calibration of the analyte flexure sensor (100). Calibration involves exposing the sensor to a series of known analyte concentrations and recording the corresponding output signals from the transducer (105). These data points are then used to construct a calibration curve or a look-up table that provides the readout interface (106) to convert the measured signal into a quantitative analyte concentration value.

[0134] The bending motion of the flexural member (101) is used for accurate sensing. In an embodiment, the primary region (102) expands or contracts in response to contact with the analyte composition (108), while the secondary region (103) remains dimensionally stable. This differential response between the two regions maximizes the bending motion and thus the sensitivity of the sensor. To further enhance this bending motion, the flexural member (101) can be implemented as a bilayer structure, with the primary region (102) as the first layer and the secondary region (103) as the second layer. This bilayer structure is formed by attaching the two layers together, for example, by covalent bonding to ensure a strong and stable connection. One or both layers of the bilayer structure can be made of a hydrogel, a material known for its biocompatibility, tunable mechanical properties, and ability to incorporate specific chemical functionalities for analyte recognition.

[0135] The act of contacting the flexural member (101) with the analyte composition (108) can be specifically controlled by disposing the flexural member (101) in a dedicated analyte composition container (109). This container (109) not only holds the analyte solution but also typically includes an immobilization member (110). The immobilization member (110) secures the flexural member (101) at a specific point or region, ensuring that the bending motion occurs in a predictable and controlled manner. This controlled bending maximizes the change in the magnetic field and enhances the sensitivity of the sensor.

[0136] These implementations of the process steps highlight the versatility and adaptability of the analyte flexure sensor (100) for achieving accurate and quantitative analyte detection. The use of a decrease in magnetic field strength as the measured signal, coupled with prior calibration, provides precise concentration measurements. The bilayer structure of the flexural member (101), with an analyte- responsive primary region (102) and a dimensionally stable secondary region (103), maximizes bending and enhances sensitivity. The use of covalent bonding to attach the layers ensures structural integrity, and the incorporation of hydrogels provides biocompatibility and tunability. Disposing the flexural member (101) within an analyte composition container (109) with an immobilization member (110) provides a controlled environment for maximizing the bending motion and thus the sensitivity of the sensor.

[0137] Data acquisition is accomplished by recording the real-time signal from the magnetometer. In one embodiment the magnetometer used is that contained within a smartphone. In this embodiment data acquisition is accomplished using the smartphone's internal magnetometer, a compact and inexpensive sensor that measures magnetic field strength in three dimensions. The hydrogel actuator is positioned proximate to the magnetometer, with the magnetic particles initially located directly above the sensor. As the actuator bends in response to the analyte, the magnetic field strength detected by the magnetometer decreases. The smartphone's internal processor then records these changes in magnetic field strength over time, providing a time-dependent signal that reflects the dynamics of the hydrogel's response to the analyte.

[0138] Analysis of the acquired data can be performed using various approaches. For small displacements, where the sensor response is linear, a simple linear calibration curve can be used to correlate the change in magnetic field strength with the analyte concentration. This calibration curve is generated by measuring the sensor's response to known analyte concentrations. For larger displacements, where angular reorientation and horizontal translation of the magnetic particles become significant, a more comprehensive mathematical model that accounts for these factors is required. Alternatively, a calibration lookup table can be created by empirically measuring the sensor's response to a wide range of analyte concentrations. This table can then be used to directly convert the measured magnetic signal into an analyte concentration value, even for non-linear sensor responses.

[0139] The detection limit of the sensor, that is, the smallest detectable analyte concentration, is determined by the ratio of the magnetic signal change to the background noise. The primary sources of noise include inherent noise of the smartphone magnetometer, magnetic noise from the hydrogel actuator itself, or random background environmental noise. The experimental results indicate that the primary source of noise in the current sensor design is the inherent noise of the smartphone magnetometer. This noise is typically on the order of 0.1 microTesla, which is consistent with the noise levels reported for commercially available smartphone magnetometer chips. Environmental noise can be mitigated by choosing a magnetically quiet location for measurements. The noise contribution from thehydrogel actuator is found to be negligible, as variations in magnetometer readings do not increase when the actuator is added to the phone. This suggests that there is significant potential for improving the sensor's detection limit by focusing on reducing the inherent noise of the magnetometer.

[0140] Response time can be tailored with respect to diffusion of the analyte into the hydrogel matrix. This can be addressed by engineering hydrogels with increased porosity, for example, by incorporating pore-forming agents during synthesis, or by reducing the thickness of the bilayer structure, shortening the diffusion distance. Further enhancements in sensitivity can be achieved by optimizing the geometry and magnetization of the magnetic particle ensemble. Increasing the volume fraction of magnetic particles within the hydrogel, or using a spherical arrangement of particles rather than a disk-shaped ensemble, can amplify the magnetic signal change, leading to lower detection limits.

[0141] Alternative actuator architectures and incorporating hydrogels responsive to other chemical and physical stimuli can provide various capabilities. For example, a buckling motion with a hydrogel pinned at two ends (FIG. 45) could enhance stability, while a twisting motion may double the signal change and increase the dynamic range. Incorporating multiple smart hydrogels with different sensitivities into a single device, coupled with simultaneous measurement along all three magnetic field axes, could provide multiplexed analyte detection.

[0142] In an embodiment, a process for making an analyte flexure sensor (100) includes providing a flexural member (101) comprising a primary region (102) and a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with an analyte composition (108) that contains an analyte to a different extent from that of secondary region (103), disposing magnetic material (104) in or on the flexural member (101), and disposing the flexural member (101) in an analyte composition container (109) comprising an immobilization member (110) configured to constrain motion of a point, edge, or area of the flexural member (101). In an embodiment, the process for making an analyte flexure sensor (100) includes the providing that comprises: forming a first layer comprising the primary region (102), forming a second layer comprising the secondary region (103), and attaching the first layer to the second layer to form theflexural member (101). In an embodiment, the process for making an analyte flexure sensor (100) includes the attaching that comprises covalently bonding the first layer to the second layer. In an embodiment, the process for making an analyte flexure sensor (100) includes at least one of the first layer or the second layer that comprises a hydrogel. In an embodiment, the process for making an analyte flexure sensor (100) includes forming the hydrogel that comprises crosslinking a polymer network. In an embodiment, the process for making an analyte flexure sensor (100) includes the providing that comprises forming the flexural member (101) with a gradient in material composition that extends from the primary region (102) to the secondary region (103). In an embodiment, the process for making an analyte flexure sensor (100) includes the disposing of the magnetic material (104) that comprises embedding a plurality of magnetic particles in the flexural member (101). In an embodiment, the process for making an analyte flexure sensor (100) includes magnetizing the magnetic particles. In an embodiment, the process for making an analyte flexure sensor (100) includes the magnetizing that comprises exposing the magnetic particles to a magnetic field. In an embodiment, the process for making an analyte flexure sensor (100) includes the immobilization member (110) that is configured to constrain motion of an end of the flexural member (101).

[0143] The process for making an analyte flexure sensor (100) involves a series of steps that integrate analyte-responsive materials with magnetic transduction components, culminating in a sensitive and versatile detection device. The process begins by providing a flexural member (101) with distinct regions that exhibit differential responsiveness to a chosen analyte. The flexural member (101) comprises a primary region (102) and a secondary region (103). The primary region (102) is fabricated from a material composition that expands or contracts in response to the target analyte, while the secondary region (103) exhibits a different degree of expansion or contraction under the same conditions. This differential responsiveness is key to the sensor's functionality as it leads to an amplified bending motion that is proportional to the analyte concentration.

[0144] The process further involves disposing magnetic material (104) in or on the flexural member (101). This step integrates the magnetic component into the sensor, enabling transduction of the mechanical deformation into a measurablechange in magnetic field strength or direction. The magnetic material (104) can be incorporated in various ways, such as embedding magnetic particles within the flexural member (101), depositing a thin magnetic film, or attaching a separate magnetic element. The choice of implementation depends on factors like the desired sensitivity, fabrication method, and cost considerations.

[0145] The next step in the process is disposing the flexural member (101) in an analyte composition container (109) comprising an immobilization member (110). The analyte composition container (109) serves to hold the analyte composition (108) during sensing, while the immobilization member (110) constrains the motion of a specific point, edge, or area of the flexural member (101). This immobilization creates a fixed reference point, directing the bending motion and maximizing the change in magnetic signal produced by the movement of the magnetic material (104). The immobilization member (110) can be a mechanical clamp, a slot within the container, or an adhesive bond, chosen based on the specific requirements of the sensor design and desired level of stability.

[0146] This process for making an analyte flexure sensor (100) offers a robust and adaptable approach for fabricating sensitive and versatile analyte detection devices. By providing a flexural member (101) with a primary region (102) and a secondary region (103) exhibiting differential responsiveness to the analyte, a measurable bending motion is generated. The incorporation of magnetic material (104) provides for contactless transduction of this motion into a magnetic signal, and the use of an analyte composition container (109) with an immobilization member (110) ensures controlled and directional deformation for enhanced sensitivity.

[0147] The fabrication of an analyte flexure sensor (100) can begin with the creation of the flexural member (101), a structure designed to exhibit a specific and measurable deformation in response to the target analyte. The flexural member (101) can be implemented as a bilayer structure comprising a primary region (102) and a secondary region (103). These regions are fabricated separately using appropriate materials and then joined together. For example, the primary region (102) may be formed from a hydrogel that is synthesized by dissolving analyte-responsive monomers and a crosslinking agent in a suitable solvent. This mixture is then poured into a mold of the desired shape and exposed to ultraviolet (UV) light or heat to initiatepolymerization and crosslinking, resulting in a solid, three-dimensional hydrogel structure. The secondary region (103), intended to be inert or less responsive to the analyte, is fabricated in a similar manner using monomers and a crosslinking agent that do not interact significantly with the target analyte. Once both regions are formed, they are attached together, for example, using a thin layer of adhesive or by covalently bonding them through a surface treatment.

[0148] Alternatively, the flexural member (101) can be fabricated as a single element with a gradient in material composition. This can be achieved by gradually varying the concentration of the analyte-responsive monomers and crosslinking agent within the hydrogel precursor solution before initiating polymerization. This gradient can be generated using a variety of techniques, such as diffusion-controlled mixing, microfluidic devices, or 3D printing methods. The resulting flexural member (101) can exhibit a continuous transition in analyte responsiveness along its length, leading to a smooth and controlled bending motion upon contact with the analyte.

[0149] Magnetic material (104) is incorporated into the flexural member structure. This can be achieved by embedding magnetic particles within the flexural member (101) during its formation. For example, magnetic particles can be dispersed in the hydrogel precursor solution before polymerization, resulting in either a homogenous distribution of magnetic material throughout the flexural member (101) or a localized spot of material if the magnetic particles are focused into one area, as may be done through the use of a temporary additional magnet placed near the flexural member to attract the magnetic particles into one defined region. The choice of magnetic material and its concentration can be tailored to optimize the sensitivity and dynamic range of the sensor. Magnetic material can be attached externally to the flexural member structure by attaching a magnetic material, or a composite magnetic material, to the structure.

[0150] Integrating the flexural member (101) into an analyte composition container (109) can include an immobilization member (110). The analyte composition container (109) can be fabricated from a material that is compatible with the chosen analyte and the operating conditions of the sensor. It can be a simple well or reservoir or a more complex microfluidic device. The immobilization member (110) is then incorporated into the container (109) to constrain the motion of a specific point, edge,or area of the flexural member (101). This can be achieved using a mechanical clamp, an adhesive bond, or a slot within the container (109). The analyte flexure sensor (100) is complete and ready for analyte detection. The sample containing the target analyte is introduced into the analyte composition container (109), allowing the analyte to interact with the flexural member (101). The resulting bending motion causes a change in the magnetic field due to the movement of the magnetic material (104). This change is detected by a magnetic field sensitive transducer, which is positioned proximate to the flexural member (101). The transducer generates an electronic signal that corresponds to the analyte concentration, which is then processed and displayed by a readout interface.

[0151] The process for making an analyte flexure sensor (100) offers flexibility in fabrication, allowing for various methods of providing the flexural member (101) and incorporating the magnetic material (104). In one embodiment, the process involves a distinct two-step approach, first providing a primary region (102) and a secondary region (103) separately, and then attaching them to form the final flexural member (101). This approach provides for greater control over the material properties and dimensions of each region. The primary and secondary regions (102 and 103) can be fabricated using methods such as molding, casting, or 3D printing, with the choice of method determined by the desired shape, size, and material properties.

[0152] The attaching of the primary and secondary regions (102 and 103) can be accomplished using a variety of techniques. Covalent bonding offers a strong and stable connection, ensuring that the layers remain securely attached during use. This bonding can be achieved through surface treatments or by incorporating reactive groups into the materials during their synthesis. Alternatively, adhesives, such as epoxies or biocompatible glues, can be used to bond the layers together.

[0153] Hydrogels are well-suited for use as either the primary or secondary region (102 or 103) due to their versatility and biocompatibility. Forming a hydrogel typically involves crosslinking a polymer network. This crosslinking can be achieved through various methods, such as using chemical crosslinkers, UV irradiation, or enzymatic reactions. The specific method used depends on the type of polymer and the desired properties of the hydrogel, such as its stiffness, porosity, and responsiveness to the analyte.

[0154] Instead of using distinct layers, the flexural member (101) can also be provided as a single element with a gradient in material composition. This gradient extends from the primary region (102) to the secondary region (103), creating a continuous transition in analyte responsiveness. Forming such a gradient can be accomplished through diffusion-controlled mixing, microfluidic techniques, or 3D printing methods that provide for precise control over material deposition and composition.

[0155] The magnetic material (104) can be integrated into the flexural member (101) during its fabrication by embedding a plurality of magnetic particles. This embedding can be achieved by dispersing the magnetic particles within the hydrogel precursor solution before polymerization, or by incorporating those into a polymer melt during molding or extrusion. The magnetic particles can be made from various materials, such as iron oxide, neodymium iron boron, or other suitable magnetic materials.

[0156] Once embedded, the magnetic particles can be magnetized to enhance their magnetic field strength. This magnetizing process can be accomplished by exposing the particles to a strong external magnetic field, either before or after they are embedded within the flexural member (101).

[0157] The immobilization member (110), an optional component within the analyte composition container (109), directs the bending motion of the flexural member (101). In one embodiment, the immobilization member (110) is configured to constrain motion of one end of the flexural member (101). This can be achieved by embedding the end of the flexural member (101) within a slot in the container (109) or by using a clamp to secure it.

[0158] These variations in the fabrication process highlight the adaptability of the analyte flexure sensor (100) and its ability to accommodate various materials, configurations, and fabrication techniques. The choice of method for providing the flexural member (101), the type and placement of the magnetic material (104), and the implementation of the immobilization member (110) can be tailored to meet specific application requirements, such as sensitivity, response time, cost, and ease of manufacturing.

[0159] The formation of the analyte flexure sensors can occur with selection and preparation of the constituent materials. In an embodiment, acrylamide (AAm) is a primary building block for both the analyte-responsive and inert hydrogel components. AAm is a readily available monomer that forms robust hydrogels upon polymerization with an appropriate crosslinker. N,N'-methylenebisacrylamide (BIS) is employed as the crosslinking agent, forming covalent bonds between AAm molecules to create the three-dimensional hydrogel network. The concentration of BIS can be adjusted to tune the mechanical properties of the hydrogels, such as stiffness and swelling capacity. In an embodiment, for glucose-responsive hydrogels, 3- (acrylamido)phenylboronic acid (3-APB) is incorporated as the glucose recognition element. 3-APB contains a boronic acid group that reversibly binds to glucose, inducing a measurable volume change in the hydrogel. This interaction can be further modulated by incorporating charged monomers, such as N-(3-dimethylaminopropyl acrylamide) (DMA), which influences the hydrogel's swelling behavior and provides fine-tuning of the initial bilayer curvature. To initiate photopolymerization of the hydrogels, either Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) or 2,2- Dimethoxy-2-phenylacetophenone (DMPA), or another similar type of agent, is employed as a photoinitiator. Additionally, thermal initiators or another type of free radical generator can be used to initiate crosslinking. Both LAP and DMPA efficiently generate free radicals upon exposure to UV light, initiating the polymerization of the acrylamide monomers and the formation of the hydrogel network. The inert portions of the hydrogel actuators are fabricated using the same monomers but without the analyte-sensitive group. To achieve a flat bilayer configuration in the absence of analyte, the concentration of DMA in the inert hydrogel can be adjusted to match the initial swelling behavior of the analyte-responsive hydrogel. Additionally, an inert polymer, such as polyethylene glycol (PEG), can be incorporated into the hydrogel precursor solutions as a pore-forming agent. PEG creates porous channels within the hydrogel network, facilitating faster diffusion of the analyte and improving the sensor's response time. In an embodiment, the magnetic component of the analyte flexure sensor includes neodymium iron boron (Nd2Fe14B) microparticles, known for their strong and permanent magnetism. These microparticles are commercially available in various sizes and grades, offering flexibility in sensor design. To prevent corrosion and ensure long-term stability in aqueous environments, the Nd2Fe14B microparticles arecoated with a protective layer of silica or encapsulated in poly-(dimethyl siloxane) (PDMS).

[0160] With regard to silica coating on neodymium iron boron (Nd2Fe14B) particles, the silica coating process for the Nd2Fe14B microparticles employs the Stöber method that forms uniform silica shells on various substrates. The microparticles are dispersed in ethanol, followed by the slow addition of ammonium hydroxide. This creates a basic environment that promotes the hydrolysis and condensation of tetraethyl orthosilicate (TEOS), the silica precursor. TEOS molecules hydrolyze in the presence of water, forming silanol groups that then condense to form siloxane bonds, creating a silica network around the magnetic particles. The reaction is allowed to proceed under continuous stirring for several hours, resulting in a uniform silica coating on the Nd2Fe14B microparticles. Alternative coating methods can also be employed, such as sol-gel processing, chemical vapor deposition, or layer-by-layer assembly, each offering different advantages in terms of coating thickness, uniformity, and process complexity. Here, a protective layer is formed that prevents corrosion of the magnetic particles while maintaining their magnetic properties and allowing for their seamless integration into the hydrogel matrix.

[0161] In an embodiment for a glucose hydrogel precursor, the glucose- responsive hydrogel formulation is based on a well-characterized and optimized composition known as GSH2.0, developed specifically for glucose sensing. This formulation uses acrylamide (AAm) as the primary monomer, crosslinked with BIS to create the three-dimensional hydrogel network. 3-APB is incorporated as the glucose- sensitive element, and DMA is added to modulate the hydrogel's swelling behavior. The molar ratio of these components can be adjusted to achieve the desired sensitivity, dynamic range, and response time. The hydrogel precursor solution is prepared by dissolving AAm in a buffered solution containing BIS and HEPES / NaOH (pH 8.15).3-APB is dissolved separately in dimethyl sulfoxide (DMSO) with sonication to ensure complete dissolution. The two solutions are then combined, followed by the addition of DMA and LAP, the photoinitiator. The final mixture is carefully homogenized to create a uniform precursor solution ready for polymerization. Alternative glucose- responsive hydrogel compositions could also be employed, utilizing different boronic acid derivatives, crosslinkers, or charged monomers. The choice of formulationdepends on factors like sensitivity, selectivity for glucose over other sugars, and desired mechanical properties of the hydrogel.

[0162] In an embodiment for an inert hydrogel precursor for glucose hydrogel actuator, the inert hydrogel for the glucose sensor is fabricated using a similar formulation to the glucose-responsive hydrogel, but without the addition of 3-APB. AAm serves as the primary monomer, crosslinked with BIS, and DMA is added to modulate the hydrogel's swelling behavior. The concentration of DMA in the inert hydrogel is carefully adjusted to match the initial swelling properties of the glucose- responsive hydrogel in the absence of glucose. This ensures that the bilayer structure lays flat when initially formed, maximizing sensitivity at the low end of the glucose concentration range. Alternative approaches to achieving a flat bilayer configuration include using a different inert monomer, such as hydroxyethyl methacrylate (HEMA), or adjusting the crosslinking density of the inert hydrogel by varying the concentration of BIS.

[0163] In an embodiment for a pH hydrogel precursor, the pH-responsive hydrogel formulation uses acrylic acid (AA) as the pH-sensitive element. AA contains a carboxylic acid group that ionizes in response to pH changes, leading to a change in the hydrogel's swelling volume. A higher pH results in greater ionization of AA, increasing the hydrogel's negative charge density and thus its swelling capacity. The pH hydrogel precursor solution is prepared by dissolving AAm in DMSO along with DMPA, the photoinitiator. PEGDA700, a polyethylene glycol diacrylate, is added as the crosslinking agent, and AA is incorporated as the pH-sensitive monomer. The molar ratio of these components can be adjusted to achieve the desired pH sensitivity and dynamic range. Alternative pH-responsive hydrogel compositions could employ different acidic monomers, such as methacrylic acid or itaconic acid, or utilize alternative crosslinking agents or pore-forming strategies to fine-tune the hydrogel's properties.

[0164] In an embodiment for an inert hydrogel precursor for pH hydrogel actuator, the inert hydrogel for the pH sensor is fabricated using the same formulation as the pH-responsive hydrogel, but without the addition of AA. AAm serves as the primary monomer, crosslinked with PEGDA700. The relative crosslinker density between the inert and pH-responsive layers is adjusted to control the initial bilayercurvature. This provides fine-tuning of the sensor's sensitivity and dynamic range at different pH levels.

[0165] In an embodiment for a synthesis of hydrogel actuators, the hydrogel actuators are fabricated using a T-shaped mold fabricated from PDMS, a biocompatible and readily moldable silicone elastomer. The mold provides a well- defined geometry for the hydrogel actuators and provides for precise control over their dimensions. The bottom, inert hydrogel layer is first partially cured under UV light with nitrogen gas flowing to create a semi-solid structure. This partial curing prevents mixing of the layers and provides precise positioning of the magnetic particles. A mixture of silica-coated Nd2Fe14B microparticles and inert hydrogel precursor is then deposited onto the partially cured layer. A permanent magnet placed beneath the mold attracts the magnetic particles, concentrating them into a disk-shaped ensemble near the tip of the vertical arm of the T-shape. The inert layer is then fully cured under UV light, entrapping the magnetic particles. Finally, the analyte-responsive hydrogel precursor is deposited on top of the cured inert layer and exposed to UV light for complete polymerization and bonding, forming the bilayer structure. The edges of the mold are used to pin the hydrogel precursors for both layers, ensuring consistent alignment and shape. After curing, the hydrogel actuator is carefully removed from the mold and hydrated by soaking in a buffer solution. For the glucose sensor, the hydrogel actuator is conditioned by alternating between solutions of 0 mM and 20 mM glucose. This cycling process provides the hydrogel to swell and shrink repeatedly, ensuring consistent and repeatable actuation. Similarly, the pH sensor is conditioned by cycling between buffer solutions of pH 4 and pH 7. Alternative fabrication methods, such as 3D printing, microfluidic techniques, or layer-by-layer assembly, could also be employed to create the hydrogel actuators. The choice of method depends on factors like desired resolution, complexity of the actuator design, and scalability of the fabrication process.

[0166] It is contemplated that analyte flexure sensor 100 and sensing an analyte can include the properties, functionality, hardware, and process steps described herein and embodied in any of the following non-exhaustive list: a process (e.g., a computer-implemented method including various steps; or a method carried out by a computer including various steps);an apparatus, device, or system (e.g., a data processing apparatus, device, or system including means for carrying out such various steps of the process; a data processing apparatus, device, or system including means for carrying out various steps; a data processing apparatus, device, or system including a processor adapted to or configured to perform such various steps of the process); a computer program product (e.g., a computer program product including instructions which, when the program is executed by a computer, cause the computer to carry out such various steps of the process; a computer program product including instructions which, when the program is executed by a computer, cause the computer to carry out various steps); computer-readable storage medium or data carrier (e.g., a computer-readable storage medium including instructions which, when executed by a computer, cause the computer to carry out such various steps of the process; a computer- readable storage medium including instructions which, when executed by a computer, cause the computer to carry out various steps; a computer-readable data carrier having stored thereon the computer program product; a data carrier signal carrying the computer program product); a computer program product including comprising instructions which, when the program is executed by a first computer, cause the first computer to encode data by performing certain steps and to transmit the encoded data to a second computer; or a computer program product including instructions which, when the program is executed by a second computer, cause the second computer to receive encoded data from a first computer and decode the received data by performing certain steps.

[0167] It can be understood that the calculations may be performed by any suitable computer system. Data is entered into a computing system via any suitable type of user interface, and may be stored in memory, which may be any suitable type of computer readable and programmable memory and is preferably a non-transitory, computer readable storage medium. Calculations are performed by processor, whichmay be any suitable type of computer processor and may be displayed to the user on a display, which may be any suitable type of computer display. The processor may be associated with, or incorporated into, any suitable type of computing device, for example, a personal computer or a programmable logic controller. The display, the processor, the memory, and any associated computer readable recording media are in communication with one another by any suitable type of data bus, as is well known in the art. Examples of computer-readable recording media include non-transitory storage media, a magnetic recording apparatus, an optical disk, a magneto-optical disk, and / or a semiconductor memory (for example, RAM, ROM, etc.). Examples of magnetic recording apparatus that may be used in addition to the memory, or in place of the memory, include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape (MT). Examples of the optical disk include a DVD (Digital Versatile Disc), a DVD- RAM, a CD-ROM (Compact Disc-Read Only Memory), and a CD-R (Recordable) / RW. It can be understood that non-transitory computer-readable media include all computer-readable media except for a transitory, propagating signal.

[0168] The articles and processes herein are illustrated further by the following Example, which is non-limiting. EXAMPLE

[0169] Quantitative, high sensitivity measurement of liquid analytes using a smartphone compass

[0170] Smartphones have led to developments in portable diagnostics. While successful, such smartphone diagnostics are predominantly optics-based, using the smartphone camera as the sensing interface. By contrast, magnetics-based modalities exploiting the smartphone compass (magnetometer) remain unexplored, despite inherent advantages in optically opaque, scattering or auto-fluorescing samples. This Example describes smartphone analyte sensing using the built-in magnetometer for signal transduction via analyte-responsive magnetic-hydrogel composites. As these hydrogels dilate in response to targeted stimuli, they displace attached magnetic material relative to the phone’s magnetometer. Using a bilayer hydrogel geometry to amplify this motion provides for sensitive, optics-free, quantitative liquid-based analyte measurements that require neither any electronicsnor power beyond that contained within the smartphone itself. We demonstrate this concept with glucose-specific and pH-responsive hydrogels, including glucose detection down to single digit micromolar concentrations with potential for extension to nanomolar sensitivities. The platform is adaptable to numerous measurands, opening a path towards portable, inexpensive sensing of multiple analytes or biomarkers of interest.

[0171] The creation and uptake of portable, easy-to-use, analysis tools is democratizing science, enabling expensive, often inaccessible, laboratory-based testing to be performed with slashed costs, improved convenience, and with less required operator knowledge. Among options such as paper-based diagnostics, wearable sensors, and other lab-on-a-chip devices, smartphone-based platforms are intriguing due to the ubiquity of phone ownership worldwide, including in remote and resource-limited areas. Their already in-built electronics and computational capabilities also offer the potential for more objective, quantitative measurements and comparisons than may be possible with other systems such as, for example, common paper-based test strips. Even so, expense associated with additional hardware requirements may still preclude their widespread deployment, such as when analyses are performed on separate equipment that simply use the phone’s screen and processing capabilities as an interface, as for example with electrochemical glucose monitors, breathalyzers, fitness trackers, and genetic marker tests.

[0172] Integrated smartphone analyses, requiring no additional sensors, power, or electronics beyond those already embedded in the phone, can provide wide dissemination. Progress has been made in this area, with the creation of mobile microscopy tools that exploit the smartphone’s built-in camera using simple attachments. Adoption of such camera-based optical techniques has now led to inexpensive smartphone-provided test platforms including mobile colorimetric or spectroscopic, fluorescence, reflectance, surface plasmon resonance, chemiluminescence, and polarimetry measurements. However, analogous use of built-in smartphone magnetometers beyond their intended compass usage, remains largely non-existent. Despite inherent advantages, including the ability to provide quantitative measurements directly from opaque samples with minimal or no prior sample preparation and being unaffected by autofluorescence and light scattering, thephone magnetometer has yet to be used for health or environmental analyte sensing or monitoring. Here, rather than using the camera or other potentially less quantitative optical modalities, magnetics-based sensing is provided to the world of smartphone analysis by pairing the integrated phone compass with magnetized, shape-changing smart hydrogel composites.

[0173] Hydrogels are hydrophilic, three-dimensional, crosslinked polymer networks that swell in water while maintaining their connected structure. With added functionalization, smart hydrogels can undergo reversible volume changes in targeted response to specific chemical or physical stimuli, making them desirable materials in multiple applications including, for example, as robotic grippers, and as actuators in sensor platforms. While some smart hydrogels have impressive degrees of analyte- induced swelling, the response for other analyte targets, such as glucose, is often limited to more modest changes (~10% in length). However, this modest change can be amplified into larger motions by engineering variations into the hydrogel composition or geometry. For example, as with metallic bimorphs within thermostats, an amplified curling motion can be created with bilayer hydrogel structures where two connected smart hydrogel layers swell to different degrees in response to a specific stimulus, or where a smart hydrogel is coupled to a second inert layer. The motion of such hydrogel structures can be described by bilayer theory for metallic bimorphs. Bilayer hydrogel structures have been created that respond to multiple stimuli, including humidity, light, pH, and temperature.

[0174] In some instances, smart hydrogels have been combined with magnetic material to create sensors that transduce hydrogel dilations (expansions or contractions) into changing magnetic field signals. However, these sensor constructs have thus far used only the dilation of uniform composition, homogeneous hydrogel materials, which shift the position of any associated (attached or embedded) magnetic material by relatively small distances, thus requiring strong magnets and / or sensitive magnetometers to detect the motion. By contrast, hydrogel bilayers can amplify the movement of any associated magnetic material, sometimes by orders of magnitude, similarly amplifying the change in any measured fields from those magnets. As shown here, this eliminates the need for large magnets, sensitive magnetometers, or even close proximity to a magnetometer and facilitates sensitive detection schemes withcheaper, less sensitive magnetometers, including those embedded within smartphones.

[0175] Point-of-use smartphone magnetometer-based sensing of liquid analytes is introduced here using a bilayer smart hydrogel structure (the hydrogel actuator, or analyte test strip) with embedded, magnetized particles that curls upon exposure to the target analyte, displacing the magnetized particles with respect to the phone magnetometer. The hydrogel actuator is demonstrated separately with both glucose- and pH-responsive hydrogels, but analogous structures can be created to target other analytes by changing the hydrogel chemistry. The dynamic range of the glucose hydrogel actuators cover typical millimolar physiological and pathological glucose ranges while also reaching high enough for bioprocessing monitoring (up to 50 mM). Due to the amplified motion of the bilayer design, the detection limit also extends down to the single digit micromolar regime (a thousand times more precise than physiological glucose levels), and sensitivities can be further scalable well into the nanomolar regime. The material cost of the hydrogel actuator is on the order of a few cents and the device can be created without any complex or expensive processes. For widespread accessibility, the positioning attachments consist only of reusable, cheap 3D printable, or castable, plastic holders that require minimal user knowledge to assemble, being not unlike common phone protectors.

[0176] Design of the magnetometer-based smartphone sensor platform. A prototype smartphone platform assembly, designed in this instance for the Motorola Moto E (2020), is depicted in FIG. 19a. The full platform consists of a positioning clamp, the hydrogel actuator, a plastic attachment with a well for the analyte solution, and the smartphone itself. The clamp immobilizes the inert horizontal segment of the hydrogel actuator to the bottom of the analyte well in proper proximity to the magnetometer. FIG.19b shows a photograph of the prototype platform assembly. The hydrogel actuator (shown schematically in FIG. 19c) is formed in a flat T-shape geometry. It consists of an inert hydrogel on the horizontal segment of the T, used to clamp the actuator in place, and a hydrogel bilayer on the vertical segment, which comprises the actuating region. The bilayer segment consists of an inert hydrogel layer on the bottom and an analyte-responsive smart hydrogel layer on the top (show in grey and in yellow, respectively, in FIG. 19c). The bottom layer also includes anembedded, roughly disc-shaped ensemble of permanently magnetized, neodymium iron boron (Nd2Fe14B) microparticles, located near the bottom tip of the T-shape. These particles are silica-coated to prevent corrosion, minimizing any unintentional changes in their magnetic field properties when submerged in test solutions. The hydrogel actuator lays flat in the absence of analyte (FIG.19c, left) and is positioned with the Nd2Fe14B particles directly above the smartphone magnetometer. The bilayer section then curls upward when analyte is added (FIG. 19c, right), due to stimuli- induced shrinking of the top smart hydrogel layer (for smart hydrogels that expand in response to the analyte, the smart hydrogel layer would be positioned on bottom). This curling moves the magnetic particles away from magnetometer, changing its magnetic field reading. FIG.19d shows a photograph of the hydrogel actuator before (left) and after (right) analyte activation. FIGs. 19e-19i show screenshots from a video of the actuator curling over time. An attachment piece was also designed for an alternative smartphone model, the Google Pixel 2, as shown in FIG.26 and FIG.27.

[0177] The system included a boronic acid-based formulation, which responds to glucose and other sugar molecules containing cis-diols, as the smart hydrogel layer in the hydrogel actuator. The hydrogel chemistry is based on the GSH2.0 formulation. which is optimized for selectivity over fructose and lactic acid. The inert portions of the hydrogel actuator were made from the same monomer components but without the sugar binding boronic acid group. The amount of N-(3- dimethylaminopropyl acrylamide) (DMA) in the inert formulation was adjusted so that the initial post-cure pure water-driven swelling of the inert and analyte-responsive hydrogels match, resulting in a mostly flat hydrogel composite in the absence of analyte (see FIGs. 28a - e). Alternatively, the hydrogel composite can also be designed to be flat at any chosen glucose level (see discussion). We also demonstrate the versatility of the platform by reworking the chemistry to switch the selectivity of the actuator to pH. This pH hydrogel actuator was created from an acrylic acid-based smart hydrogel paired with an inert hydrogel layer such that it lays flat at pH 4 and swells with increasing pH. While the glucose hydrogel actuator has a shrinking glucose layer on top, here an expanding smart hydrogel layer is placed on the bottom of the hydrogel actuator so that the bilayer still curls upward and away from the phone surface (and magnetometer) as the pH increases. We achieved equivalent controlover initial bilayer curvature of pH hydrogel actuators by tuning the relative cross-linker density between the inert layer and responsive layer.

[0178] System characterization. Basic characterization of a glucose platform is shown in FIG.20. FIG.20a shows changes in measured field strength ( ^Bz) as the glucose concentration of a test solution is raised to 20 mM and then returned to zero (see FIGs.29 and 30 for data). Tested over three cycles, as shown in FIG.20b (see FIG.31), the actuator accurately reproduces this response with standard deviation of the average endpoint magnetometer readings of no more than a half percent of the total response (see FIG.20c). The hydrogel actuator used here had an average ^Bzof 87 mT with a response time of roughly 20 minutes in response to 20 mM glucose, (see FIG.32). However, this observed change in field depends on how far the hydrogel actuator moves the magnetized particles as well as on the magnetic field generated by those particles, both of which can be increased many fold. FIG.20d shows that the glucose platform responds dynamically to changes in glucose concentration over several orders of magnitude. Similarly, basic characterization of the pH-responsive platform is shown in FIGs.33-36. In addition to repeatability to within 1% of the pH- responsive platform over multiple trials on the Moto E, we also show similar repeatability on the Google Pixel 2 (see FIGs. 34 and 35), as well as high reproducibility, ~3%, between two smartphone models (FIG. 35c and 35d). Finally, with the pH platform, we also demonstrate a ~2x speed improvement by simply adding polyethylene glycol (PEG) to the hydrogel precursors, and a further ~2x speed improvement by making the bilayer thinner (see FIGs. 37a and 37b), while further improvements in response time are possible through optimization of these strategies. Alternatively, exploiting differences in initial response rates of the sensors, indicates that methods could also be developed for sub-minute tests (see FIGs.37c and 37d).

[0179] While, for clarity, FIG.19d and FIGs.19g-19i show a large degree of deflection from the bilayer in response to glucose, most of the ^Bzinduced by this iteration of the hydrogel actuator occurs with a smaller degree of deflection, in a range where the magnetic particles are moving mostly vertically with little change in their angle in relation to the phone surface and where the sensor response remains largely linear (see discussion). For example, the endpoint magnetometer readings of FIG.20d (inset) are reproduced in FIG.21a, with a straight-line fit revealing an approximatelylinear calibration (R2= 0.985) of the glucose platform over two orders of magnitude. Similarly, the pH platform yields approximately linear calibration (R2= 0.989, FIG.21b and FIG.36) over a pH range that covers 80% of the sensor range.

[0180] Detection limit. Despite large dynamic ranges, the platform can detect remarkably low glucose concentrations due to the amplified motion of the bilayer design. As shown in the results from another hydrogel actuator (FIG.22a, with data in FIG. 38), the detection limit for glucose reaches single digit micromolar concentrations. This is already on par or better than most optical and electrochemical glucose sensors but can likely still be improved. Detection sensitivity is limited by noise, which is here dominated by the inherent noise of the phone magnetometer rather than by the hydrogel actuators themselves, which can be seen to not appreciably change the overall noise when added to or removed from the phone (see FIG. 22b, FIG. 39). Nor does the noise change during actuation (see FIG. 40). Therefore, with the noise dominated by the phone rather than the hydrogel actuator, numerous plausible routes exist to extend detection limits well into the nanomolar range through simple geometrical and / or magnetic changes to the actuator. Possible changes to the actuator geometry are detailed more fully in the discussion section below but as first demonstrations, we include here two elementary magnetics-based modifications: (i) increasing the loading of magnetic material to increase the observed ^Bz~10x (FIG.22c, left) with only a minimal penalty in terms of noise (FIG.22c, right), and (ii) reducing the distance between the hydrogel actuator and magnetometer to yield a further two orders of magnitude increase in magnetic field reading (FIG.22d).

[0181] Real-world sample testing. As elementary real-world examples, in FIG.23a, we demonstrate smartphone-provided testing of sugar content in wine and champagne, without any pretreatment other than dilution in buffered water (because the particular actuator used was too sensitive). As expected, the high sugar wine (sangria) induces a bigger ^Bzthan do the low sugar options, pinot grigio and champagne brut. In FIG.23b we demonstrate a simple first application of pH sensing with the smartphone-based testing of various common beverages, with no pretreatment. No buffers were used here since remnant pH buffer in the well can alter the pH of subsequent test solutions; instead ^Bzwas recorded from a baseline of tap water (pH ~ 6.5) where the pH hydrogel actuator starts out curled and then flattens asthe pH decreases. The pH’s of the beverages were also measured with a standard pH electrode for comparison (see FIG. 23b). The lower pH beverages yielded larger changes in ^Bz, as expected.

[0182] The sensor platform includes a magnet being moved by a hydrogel. An adaptation of such a system for smartphone-based sensing and for high-sensitivity measurements with a magnetometer within a phone involves amplifying the change in the magnetic field by amplifying the motion of the magnet. For a block of hydrogel with uniform composition that dilates in response to some stimulus by some fraction, ^, of its length, L, an attached magnet would move a distance ^ ∙ L. For a bilayer hydrogel strip such as those used here, however, a magnet attached to its end would instead move a vertical distance of approximately 3 ^ ∙ L2 / 4h where h is the thickness of the bilayer. The magnet motion is therefore amplified over that achieved by attachment to a simple hydrogel by a factor of order L / h or proportionally to the geometric aspect ratio of the bilayer strip. Increasing device sensitivity thus translates into a problem of geometric design, rather than one fundamentally limited by intrinsic chemistry or material properties. This provides measurement sensitivities that are already, even with relatively short bilayer strips, of order 100- to 10,000-fold greater than comparable alternatives as well as measurement with different hydrogels that might offer only minimal material expansions.

[0183] For the hydrogel actuator above, the embedded magnet included a thin, disc-shaped pod of Nd2Fe14B microparticles. This disk of microparticles was permanently magnetized out-of-plane, normal to the disk’s flat surface, such that the disk’s magnetic field points towards the magnetometer when the hydrogel is laid flat on top of the phone. The field from this system can be modelled by an imaginary Amperian surface current loop flowing around the disk circumference with a current density equal to the disk magnetization, M. The field Bz at a distance z away from the disk of thickness d (assumed small) along its central axis is thus equal to that of a circular loop carrying a current of magnitude i = Md, which yields: ^^ ^^ ^^ଶ ^ ଶ^^^ ^ ∙ ^^ ^^ ^^∙ ^^where R is the radius of the disk and ^0 is the vacuum permeability. Taking Z0to be the distance from the magnetic disk to the magnetometer within the phone, for small hydrogel fractional dilations, ^, and correspondingly small changes in distance, ^z =3 ^ L2 / 4h, the measurable change in field, ^Bz ≡^^^ ^^௭⁄^^ ^^^∙ ^z, is linear in ^ and givenby: 9^^ ^^ ^^ ^^ଶ ^ ଶ∆ ^^ ^ ^ ∙ ^^ ∙ ^^ ^^௭8 ହ^2^^^^ଶ ^ ^^ଶ^ ℎ

[0184] ൌ ^2⁄3 ∙ ^^^, that maximizes this field change and yields a simplified expression linearly proportional to the original, analyte concentration-dependent hydrogel dilation, ^, with proportionality constant determined by the actuator’s geometric and magnetic properties: ^ / ଶ^3 ^^ ^^ ଶ∆ ^^ ^^ ^^௭ ^ ∙^^ଶ∙ ^^ ^3^

[0185] separation Z0 from the magnetometer significantly increases the measured signal, ^Bz. But, at least for smartphone-based sensing, this approach is limited by the depth to which the magnetometer is buried within the phone, which is around 3 to 5 mm for many phones. For the work presented here Z0 was just short of 5 mm and thus using a phone model with magnetometer closer to its surface would improve sensitivity. Indeed, placing the actuator directly atop a bare magnetometer itself could increase ^Bzby as much as two orders of magnitude (see FIG.22d), but such setups are not readily available. Instead, restricting attention to smartphone-based sensing, amplifying the hydrogel motion provides a more accessible method to boosting sensitivity. Increasing hydrogel motion can, to some degree, be achieved through modifying the hydrogel chemistry (e.g., increasing the amount of analyte responsive monomer or decreasing the crosslinking degree) to increase ^, but this approach is materials limited and hydrogel- and analyte-specific. Instead, reducing the actuator thickness, h, or increasing its length, L, can boost sensitivity, linearly and quadratically, respectively, for any hydrogel material. Additionally, sensitivity can be increased byincreasing the total magnetic moment, m, of the magnetic disk through increasing either the disk thickness, d, or its magnetization M, by increasing the volume fraction of magnetic microparticles comprising the disk (as seen in FIG.22c, left).

[0186] The above assumes that the disk moves only vertically above the phone with negligible horizontal translation or angular reorientation of the disk. While true only for small displacements, such displacements do describe a considerable fraction of the sensor dynamic range. For example, as can be determined by substitution into Equation 1, for the typical length-scales involved, a 50% drop in measured field is achieved by raising the magnetic disk just 1 to 2 mm above the phone surface. This entails minimal angular reorientation or horizontal translation of the magnetic disk. Also, provided the height that the disk is raised remains small compared to Z0, the sensor remains close to linear in ^. Such linearity is experimentally evident in both the glucose and the pH sensing data (see FIGs. 21a and 21b, respectively) and shown also theoretically in FIG. 43. For larger hydrogel bilayer curlings, however, there can be appreciable angular reorientation of the disk magnetic moment. Under such circumstances, Equation 3 is no longer valid, and converting ^Bzinto a concentration value requires either prior calibration or a more complete mathematical treatment that remains valid for arbitrarily large hydrogel curlings and accounts for both vertical and horizontal translation as well as angular reorientation.

[0187] Detection limits depend on the ratio of ^Bzto background magnetic noise. Such noise may come from the phone magnetometer (and the phone itself), the magnetic hydrogel actuator, as well as random background environmental sources, although such sources can often be rendered negligible by moving to a magnetically quieter spot in the room, without needing any magnetic shield. Once that is done, the data suggest that the noise is dominated by the intrinsic noise of the smartphone magnetometer, since random variations in the magnetometer readings do not increase when the magnetic hydrogel actuator is placed on the smartphone (FIG.22c, FIG.39). Nor does the noise level depend on the height of the hydrogel magnet above the phone or the degree of curling in the bilayer (see FIG. 40). This conclusion is further corroborated by the standard deviation of the residuals in ^Bzreproducibly being on the order of 0.1 ^T (FIG. 22b), which is the typical noise level for smartphonemagnetometer chips24. Combined with the scalings in Equations 2 and 3, the negligible noise from the hydrogel actuators suggests that there remains considerable room to improve the system detection limits.

[0188] With its single digit micromolar detection limit, the current proof-of- concept system is already of order 1000x more sensitive than typical blood glucose levels, but this was achieved with bilayers that were just 16 mm in length, L, and 0.65 mm thick, h. Without exceeding the size of a typical smartphone, actuator lengths could be increased at least 5-fold, while thicknesses could likely also be reduced by a similar factor, yielding a further combined sensitivity enhancement of order 100 based on geometrical considerations alone. Additionally, the disk-shaped magnets comprised only sparse ensembles of embedded magnetic particles none of which were necessarily high-grade neodymium, but simply what was readily available. These disks produced only small fields at the phone magnetometer of order 100 mT, whereas phone magnetometer chips typically measure up to as high as 5,000 mT. This is not to say that field strengths could just be increased 50-fold without introducing additional magnetic noise, but initial tests are promising: attaching a poly-dimethylsiloxane (PDMS) disk infused with a higher volume density of magnetic microparticles to the actuator, which yielded 10 times the field at the magnetometer, increased the observed noise by only 10% - 15% (see FIG. 21c), although this might also be due simply to insecure attachment of the disk to the hydrogel actuator compared to the truly embedded particles used above. Assuming the above geometric enhancements similarly do not introduce excessive additional noise, ultimate detection limits may reach well into the nanomolar range or beyond.

[0189] The dynamic range of the glucose hydrogel actuator covers both normal and pathological ranges for both blood and saliva as well as ranges typically encountered in bioprocess, but with maximum sensitivity around 0 mM, when the actuator is flat and as close to the magnetometer as possible. This actuator was designed to lay flat in the absence of glucose since highest sensitivity is typically desired for lower concentration range applications. However, the bilayer can be biased to lay flat, and therefore offer maximal sensitivity, at any desired glucose concentration by adjusting the DMA content in the inert layer (FIGs.28a - 28e).

[0190] Hydrogel materials have widely tunable properties that can improve the platform. While the portability of the platform makes it preferable to shipping test samples to a laboratory with specialized staff in terms of time required to complete an analysis, the response time can be increased. FIG. 37 shows that adding PEG to introduce gel porosity already more than doubles the actuation speed, but optimization of this technique to the point where a continuous porous network is formed can improve the response time further, with a few minutes as an achievable goal. In addition to increasing the motion of the hydrogel actuator (as per Equation 3), reducing the bilayer thickness also reduces the distance for the analyte to diffuse into the hydrogel. Given the diffusive nature, response rates can increase quadratically with reductions in thickness, suggesting plausible response times on the seconds, rather than minutes, timescales. Fabrication methods such as 3D-printing, or spin-coating, may help achieve thinner and more reproducible, structures. Thinner and / or more porous hydrogels may result in mechanically weaker structures, but this can be counteracted by increasing the strength of the hydrogel with established methods, such as by increasing the concentration of crosslinker, creating interpenetrating networks, and adding inorganic fillers. Antifouling materials can be incorporated to protect the hydrogels.

[0191] Additionally, alternative actuator architectures can provide diverse analyte targets to the platform. While a bilayer curling motion was chosen here to amplify signal when compared to simpler uniform hydrogel slabs, alternative geometries would offer different features. For example, a buckling motion with a hydrogel pinned at two ends, instead of only at one, may enhance stability. A twisting hydrogel motion can provide field direction to switch from negative to positive, doubling the possible signal change and increasing the dynamic range if the number of times the field direction switches between each 180° twist of the hydrogel actuator is tracked. In addition, in the current work, the field change is primarily along the z-axis of the magnetometer; simultaneous measurement along all three field axes, as is possible with most smartphone vector magnetometers, could provide multiplexed designs where multiple smart hydrogels that either actuate in different directions or contain magnetic particles magnetized in different directions are incorporated into a single device. Finally, in addition to glucose and pH, smart hydrogels are commonly designed to respond to other chemical and physical stimuli such as light, ionic strength, andtemperature. As with the glucose-responsive hydrogel, other analyte binding groups could also be incorporated to make gels responsive to other biologically relevant targets such as Na+, K+, lactate, and enzymes. Smart hydrogels utilizing advanced targeting techniques, such as molecularly imprinted polymers and complementary nucleic acid sequences, give the ability to tailor their response to specific proteins and DNA sequences, further multiplying possible use cases for this new form of smartphone-based sensing. Potential applications are envisioned for home-based quantification of chemical contaminant levels in tap water; for food testing of other opaque liquids such as orange juice, milk, coffee, wine, or soups; for environmental analysis, such as for analyzing possibly murky lake or stream water in remote locations; and for mobile health analysis, such as with remote analysis of blood, sweat, urine, or saliva.

[0192] Ensuring accurate readings in such complex, real-world samples, will require addressing issues of imperfect hydrogel selectivity, a consideration inherent to any hydrogel-based sensor. For example, boronic acid-based smart hydrogels also respond to ionic strength, temperature, pH, and other sugars, so these interferants can be co-monitored or the hydrogel chemistry modified to render their contributions negligible. The incorporation of quaternary amines into a boronic-acid hydrogel can be used. Alternatively, biological enzymes are selective for biomolecules such as sugar and can increase sensor specificity. For a phone sensor, signal and interferant contributions can be deconvolved by exploiting the vector nature of smartphone magnetometers to provide simultaneous measurement of three hydrogels with different sensitivities to different interferants.

[0193] The system can include sensors, electronics, and power included in the smartphone, wherein the hydrogel actuator test strip and a positioning attachment can be recycled for repeat measurements. While new test strips may be desirable for each analysis to avoid cross-contamination, they are inexpensive and reversible, making individual actuators also suitable for applications that require continuous monitoring. Estimated material costs of the hydrogel actuators are $0.16 for glucose hydrogel actuators (see Table 1) and $0.03 for pH hydrogel actuators (see Table 2), based on the price of the materials in the small quantities we purchased, though bulk purchasing would substantially further decrease costs. The concept presented herewas demonstrated on two smartphone models, the Motorola Moto E (2020) and Google Pixel 2, though it is adaptable for any smartphone with a magnetometer, which is nearly all in the current day. A consideration when adapting for a new phone model is ensuring that the magnetic particles are positioned over the magnetometer, which may be located differently on different phones, but the attachment piece can be 3D printed to fit any model. Additionally, the size of the liquid-containing well in the attachment, as well as the hydrogel actuators themselves, can be tailored to the desired samples.

[0194] Magnetics in smartphone-based sensing provides an optics-free, quantitative transduction mechanism that provides numerous mobile sensing applications beyond just the glucose and pH sensing demonstrated here. Magnetics- based smartphone analysis provides for quantitative measurements within liquids that are opaque or otherwise optically unclear, often without sample pre-processing and without concern for interference from variable background lighting, which may affect the accuracy of optically based measurements. Using just a smartphone compass, the system shows dynamic ranges up to four orders of magnitude, and single digit micromolar detection limits (for glucose). Potential scalability down to nanomolar detection ranges opens additional possibilities of working with highly diluted samples when original sample volumes might be small or hard to acquire. Combined with the ability to target hydrogels to different analytes and to potentially run multiple hydrogel actuators simultaneously, magnetics-based smartphone measurement can provide useful, home-based or point-of-use analyses with minimally invasive small samples such as minimal test quantities of fluid, or even individual drops of blood.

[0195] Silica coating on neodymium iron boron (Nd2Fe14B) particles. For rustproofing, the Nd2Fe14B particles were coated with SiO2 through the hydrolysis and polycondensation of TEOS, also known as the Stöber method, by following a procedure described by Kim et al.. Briefly, 40 g of Nd2Fe14B particles are vigorously mixed in 1000 mL of ethanol with magnetic stirring. Next, 60 mL of 29% ammonium hydroxide is slowly added, followed by 2 mL of TEOS. The mixture was then stirred for an additional 12 hours before washing with ethanol.

[0196] Glucose hydrogel precursor. The glucose hydrogel composition is derived from the GSH2.0 hydrogel devised in Nguyen et al. Stock solutions of 2 wt%BIS in HEPES / NaOH, pH =8.15 and 2 wt% LAP in deionized water were created for hydrogel syntheses. Hydrogel precursor solution was then made with the following: 172 mg AAm was dissolved in 500 mL of 2% BIS solution while 55 mg of 3-APB (for glucose responsiveness) was dissolved in 223 mL DMSO with 10 min. of sonication. These two solutions were combined before adding 95 mL DMA and finally 105 mL 2% LAP, used as a photoinitiator. The final mixture had a molar monomer composition of 73.3% AAm, 8.8% 3-APB, 15.9% DMA, and 2% BIS.

[0197] Inert hydrogel precursor for glucose hydrogel actuator. The same stock solutions of 2 wt% BIS in HEPES / NaOH, pH =8.15 and 2 wt% LAP in deionized water were created for hydrogel syntheses.230 mg AAm was dissolved in 500 mL of 2% BIS solution, to which 223 mL DMSO, 52 mL DMA, and 105 mL 2% LAP (used as a photoinitiator) were added. The final mixture had a molar monomer composition of 90% AAm, 8% DMA, and 2% BIS.

[0198] The pH hydrogel precursor.0.4 g of AAm were dissolved in 0.9 mL DMSO, along with 10 mg of 2,2-Dimethoxy-2-phenylacetophenone (DMPA), used as a photoinitiator. 300 mL of PEGDA700 were added as a crosslinking agent, and 100 mL AA for pH-responsiveness. The final mixture had a molar monomer composition of 79.3% AAm, 0.2% PEGDA700, and 20.5% AA. For the introduction of PEG, 0.45 mL of DMSO was replaced with 0.45 mL of an aqueous solution of PEG at 0.4 g / mL.

[0199] Inert hydrogel precursor for pH hydrogel actuator.0.4 g of AAm were dissolved in 0.9 mL DMSO, along with 10 mg of 2,2-Dimethoxy-2- phenylacetophenone (DMPA), used as a photoinitiator.300 mL of PEGDA700 were added as a crosslinking agent. The final mixture had a molar monomer composition of 79.3% AAm, 0.2% PEGDA700, and 20.5% AA. The final mixture had a molar monomer composition of 99.8% AAm and 0.2% PEGDA700. For the introduction of PEG, 0.45 mL of DMSO was replaced with 0.45 mL of an aqueous solution of PEG at 0.4 g / mL.

[0200] Synthesis of Hydrogel Actuators. Hydrogel actuators were synthesized in a T-shaped PDMS well with 0.5 mm depth. The bottom layer of the structures was partially cured under UV light (365 nm, 4W) with N2gas flowing.Hydrogel precursor mixed with silica coated Nd2Fe14B particles was then deposited on top of the partially cured bottom layer, and particles were focused into a local disk with the placement of a separate permanent magnet placed below the PDMS mold. UV light (365 nm, 4W) was applied with N2gas flowing to fully cure and bond both layers, entrapping the Nd2Fe14B particles. The edges of the well were used to pin the hydrogel precursors for both layers. The Nd2Fe14B particles were magnetized by briefly placing the hydrogel actuator into the bore of 3T MRI scanner. The glucose hydrogel actuators were swelled in HEPES / NaOH, pH = 7.4 buffer solution after curing and conditioned by alternating between 0 mM and 20 mM glucose solutions 3x. pH hydrogel actuators were swelled in pH 4 buffer solution after curing and conditioned by actuating in pH 7 buffer and returning to baseline in pH 4 solution.

[0201] For data collection and initial testing and development, it was beneficial to adjust the fit of the attachment piece with shims so that the magnetic particles could be moved directly over the magnetometer for various iterations of the hydrogel actuator during development. We used many differently shaped attachment pieces including those shown in FIG.24a and FIG.24b. The platform in FIG.24a and FIG. 24b represents a compact version, where the attachment piece snaps snugly onto the phone without shims and with the magnetic particles of the hydrogel actuator automatically positioned directly over the magnetometer. The size and formulation of the hydrogel actuator can be standardized to use the type of assembly shown in the prototype. Adapting the magnetometer-based smartphone sensor to other smartphone models involves changing the location of the analyte well to place the magnetic material over the magnetometer of the smartphone. As an example of a different phone, FIG. 26 shows an attachment piece designed for a Google Pixel 2 smartphone.

[0202] To ascertain whether potential fluctuations in the background magnetic field might interfere with the sensor readings, two smartphones were used for data collection, one containing the full sensor platform (sensor phone) and one stationed nearby with no additional hardware (background phone). Both phones were calibrated to the background magnetic field before testing. FIG.29 shows a sample of the raw data collected (from FIG. 20B, 20mM reversibility cycle 2) during an experiment. The magnetic field reading, ^^, from the background phone (FIG. 29a)confirms that there is little change in the background magnetic field over the course of an experiment, with total fluctuations in the vector components ^^௫, ^^௬, ^^௭, and in ^^௧(the total field) each on the order of ∼ 1 ^^T or less. The magnetic field reading, ^^, of the sensor phone (FIG. 29b) shows that most of the change in magnetic field in response to 20mM glucose is a result of sensor actuation is in the ^^-direction, with minimal changes in ^^௫and ^^௬. The change in ^^௧closely mirrors the change in ^^௭,which has a large negative value. This is expected since the embedded ensemble ofNdଶFe^ସ B particles were magnetized axially and with negative ^^-direction pointeddownward into the phone. The particles were magnetized axially instead of in-plane to maximize the magnetic field reading. The magnetic field reading of the background phone was subtracted from that of the sensor phone to obtain a background- subtracted signal where variations in the background magnetic field are controlled for (FIG. 29 ^^). The signal of the magnetometer-based smartphone glucose sensor is generally considered to be the change in ^^௧from a 0mM glucose baseline of the background-subtracted signal (FIG. 29d). In this work, ^^௫and ^^௬are negligible, making ^^௧approximately equal to ^^^, and so from here on we refer to the signal of the magnetometer-based smartphone glucose sensor as Δ ^^௭. While full background subtracted data is presented here, such background subtraction is only necessary in noisy magnetic environments. In practice there was never a substantial difference between the raw (sensor phone) and background-subtracted data in any of the data, and only one phone is necessary for implementation of the magnetometer-based smartphone sensor.

[0203] The reverse response of the hydrogel actuator (going from high glucose concentration to low glucose concentration) is slower than the forward response ( 0 to 20mM ). For each cycle, the magnetic field reading (B) was recorded in 0mM glucose solution for 1 hour, changed to 20mM glucose for 1 hour, then changed back to 0mM glucose. The 0mM glucose solution is then refreshed several times over several hours to return the magnetometer reading to its initial value (FIG. 30). FIG.31 shows the Δ ^^௭over three cycles of activation with 20mM glucose. Solution changes are marked by brief downward spikes in the trendline, which occur due to the hydrogel actuator being pressed flat against the bottom of the well due to capillary forces in the absence of solution. Due to the high responsiveness of the sensor at lowconcentrations of glucose, thorough washing is required to return the magnetometer reading fully to baseline. Slow elastic relaxation of the hydrogel may also contribute to a slower reversible response of the sensor, even after all remnant glucose has been washed out, such as can be seen after the final wash step in cycle 3 (FIG.31c). While the low cost of the device provides for its use as a disposable test strip, this data shows the sensor can be used for continuous monitoring.

[0204] FIG.32 shows the change in field strength ^Δ ^^௭^ in response to the three cycles of 20mM glucose fit to a one-phase association curve, ^^ ൌ ^^^^ ^ Plateau െ ^^^^ ∗ ^1 െ exp ^െ ^^ ∗ ^^^^ with ^^^is the ^^-intercept, Plateau is final value of the response, and ^^ is a rate constant. Data before the inflection point in the response, seen at ∼ 4.5 minutes in all three cycles, were excluded from the fit. This initial phase of the response is explained by the hydrogel resting on a bar placed toward the end of the bilayer section of the actuator while the bilayer is mostly flat in 0mM conditions. This supporting bar was only necessary to prevent an initial response where the magnetometer reading decreased instead of increased, which occurred only in iterations of test hydrogel actuators where the initial curvature of the bilayer was slightly downward instead of flat or slightly upward. The slower initial phase of the response corresponds to the bilayer changing its curvature from downwards to upwards while being supported by the bar, and the accelerated rate of response after the inflection point at ∼ 4.5 minutes corresponds to when the sensor has activated sufficiently such that it is no longer supported by the bar and is now freely travelling upwards and away from the phone surface through the 20mM glucose test solution. The slope increases roughly 4x at this point, meaning a factor of four sensitivity is likely lost at the low end of the response before the hydrogel actuator lifts off the bottom of the well. If the initial curvature of the bilayer is flat or slightly upwards, such as the iteration used in the future detection limit test, then the bar is not necessary (which can be the case for all future systems). Shims can also be used underneath the inert, horizontal section of the hydrogel actuator to raise it up so that the bilayer section does not rest on the bottom. In these cases, the response is single phase. The response time ( Tଽ^) was defined as the time it takes for Δ ^^௭to reach 90% of the plateau value. The Tଽ^of the measured responseto 20mM glucose was determined to be 19.4, 19.0, and 19.6 minutes for cycles 1, 2, and 3, respectively.

[0205] The pH-responsive platform was characterized in terms of reversibility (FIG. 33), reproducibility of the response (FIG. 34 and FIG. 35), and dose / response calibration (FIG.21b, FIG.39). The pH hydrogel actuator is designed to lay flat in pH4 solution. When the buffer is changed to pH7, the bilayer portion of the hydrogel actuator curls and moves the NdଶFe^ସB away from the magnetometer, increasing Δ ^^௭. When the solution is changed back to pH4, the bilayer flattens and the magnetometer reading returns to baseline, as shown in FIG.33. Here, the response of a single pH hydrogel actuator from pH4 to 5 was tested 3x each on the Motorola Moto ^^ (2020) and Google Pixel 2, alternating between the two, with the resulting response curves shown individually in FIG.34a and FIG.34f. Then, the response was again tested but with the Google Pixel 2 attachment piece affixed to the Moto E, but laterally shifted for different magnetometer placement in such a way that the magnetic field reading was maximized when the bilayer was flat. The hydrogel actuator was reset to baseline in pH4 buffer before each trial, and shims were used underneath the inert clamping region of the actuator to adjust its position vertically, so that the baseline ^pH4^ magnetometer value matched for each trial. A noisier signal is seen in the Google Pixel 2 trials, indicating that this (refurbished) phone model contained a noisier magnetometer than the one in the Moto E.

[0206] FIG. 35a shows the three response curves from the Moto E trials overlaid. The response is highly repeatable, with the standard deviation of the endpoint magnetometer response being just 0.56% of the total change in magnetic field reading. FIG.35b shows the three response curves from the Google Pixel 2 trials overlaid. The response is also highly repeatable on this phone model, with the standard deviation of the endpoint magnetometer response being just 1.2% of the total change in magnetic field reading. The response is also reproducible between the phone models. FIG.35c shows the 33rd magnetometer response curve from both the Moto E and the Google Pixel 2, as well as the control trial where the Google Pixel 2 attachment piece was affixed to the Motorola Moto E. This plot shows that the shape of the response curve is only slightly different when using the Moto E vs. the Google Pixel 2. The control trial (yellow) matches the standard Motorola Moto E trial (orange), indicating that thedifference in the shape of the response curves is due to a difference in the sensitivities of the two magnetometers at different points in space, rather than being an artifact of the different attachment pieces. Despite the difference in the shape of the response curves, the endpoint magnetometer readings are in good agreement. FIG.35d shows the average and standard deviation of the endpoint magnetometer response for the three Moto E trials and the three Google Pixel 2 trials, with a difference of just 2.7 ^^T. This data shows that the response of the pH platform is also stable over at least 4 days (the duration over which these multiple experiments were performed) and many actuation and washing cycles.

[0207] FIG. 37 shows that the response time of a hydrogel actuator is improved by adding Polyethylene Glycol 10,000 (PEG), serving as a pore-forming agent, to the precursor solutions for both the inert and active layers, as well as by making the active layer thinner. This was demonstrated on a pH-responsive hydrogel but could be applied to the glucose hydrogel actuator as well. FIG.37a shows the raw field strength recording for pH hydrogels made with (red) and without (blue) PEG, and with both PEG and a thinner active layer (green), and the resulting response curve when the test solution is changed from pH4 to pH5, causing the actuators to curl from an initial flat state. The background-subtracted field strength is plotted rather than Δ ^^௭to show that the response curves plateau at or above ∼ 26 ^^T, meaning that they are still well within range of the magnetometer. This was done to avoid response times of the hydrogel actuators that may appear artificially fast if the bilayers curl to a degree where the magnetic particles move out of range and the magnetometer reads ∼ 0 ^^T. The red, blue, and green curves start at different field strengths only because the different actuators had different initial offset distances from the base of the test fluid container and / or different magnetic particle loadings; this does not affect response time as can be seen in FIG.37b which shows the normalized response curves, clearly demonstrating the improved response time when PEG is added and / or the bilayer is made thinner. The Tଽ^of these hydrogel actuators improves from approximately 47 minutes without PEG to approximately 23 minutes with PEG, and further to 13 minutes with both PEG and a thinner active layer, a roughly 2 ^^ improvement with each step. These results make the response time on par with an at-home COVID test.

[0208] In FIG. 37c and 37d, we present another method of signal transduction that can provide faster, sub-minute measurements. FIG.37c shows the standard sensor response to various pH levels, with a Tଽ^on the order of 15 minutes before the signal stabilizes. FIG.37d shows the same data but zoomed into the first 30 seconds. Taking either Δ ^^௭after 30 s or the initial slope of the response to be the sensor signal can provide the user to discriminate between pH levels, even with additional noise introduced from the hydrogel settling after the solution change, as shown in FIG.37d.

[0209] To probe the detection limit of the smartphone magnetometer-based sensor, Δ ^^௭was recorded in response to five different concentrations of glucose, with 3 replicates each. FIG. 21A is reproduced with error bars showing the range of Δ ^^௭recorded over the three replicates in FIG.38a. FIG.38b shows the average Δ ^^௭for all five glucose concentrations recorded. The average Δ ^^௭was calculated at the end of each run, between 119 and 120 minutes for each concentration to determine a calibration curve, shown in FIG.38c. A linear regression was applied to determine the response equation. An estimate of the limit of detection (LOD) is then determined at approximately 8mM based on the formula ^^ ^^ ^^ ൌ 3.3 ^^, where ^^ is the slope of the fit equation (0.039) and ^^ is the standard error of the ^^-intercept determined from the linear regression (0.092). While this single-digit micromolar limit of detection is reached for the current proof-of-concept, future optimization of the design can decrease this value substantially.

[0210] Magnetic field as a function of bilayer curvature. For small deflections of the hydrogel bilayer, the embedded disk of magnetized particles translates essentially vertically above the phone magnetometer and the field measured at magnetometer scales linearly with the hydrogel fractional expansion (see Equation 3). In this limit of small hydrogel deflection, the sensor is both most linear and at its highest sensitivity, and if potential ranges of analyte concentrations are known, the hydrogel bilayer system can be designed to operate within this regime.

[0211] However, larger hydrogel bilayer deflections can be used (as seen, for example, in FIGs. 19e-19i and FIG. 41). Larger deflections extend the dynamic range of the sensor but also lead to angular reorientations of the disk of magnetized particles, changing the direction of its magnetization with respect to the phone. Suchdeflections also cause not only vertical, but also horizontal, translations of the disk. For these larger deflections a calibration look-up table can be used to translate between field measurements and analyte concentrations, but it is also possible to analytically predict the field dependences even in these more complex situations, which for completeness we derive below.

[0212] The bending of thin bilayer beams due to differences in the expansion or shrinking of their two composite layers was studied for a bimetallic strip that bends when heated. This Example describes mechanical deformation of a hydrogel bilayer strip, clamped at one end and with magnetized particles embedded at the opposite free end, with the goal of quantifying how hydrogel expansions / contractions in response to targeted analytes change the magnetic field measured by a magnetometer located beneath the free end of the bilayer strip. We start by rewriting the general expression found in

[0034] for the bilayer curvature, 1 / ^^, by replacing a difference in metallic thermal expansion factors with instead the fractional expansion,^^, of the active hydrogel layer in our bilayer strip to give:16 ⋅ ^1 ^ ℎ^ଶ^ଶ ^^^^ൌ^^ ଶ ^ ^ ^ ^ ଶ ^⋅ ^ ^^1^where ℎ^ଶis thein the bilayer strip, ℎ ൌ ℎ^^ ℎଶis the total bilayer thickness, and ^^^ଶis similarly the ratio of Young's moduli of the top and bottom layer materials (see FIG. 41). The above assumes that only the active layer dilates, but if both layers dilate simultaneously the same analysis still applies, only with ^^ replaced by the difference in expansion factors for the two hydrogel layers. It is also assumed that the hydrogel bilayer is oriented such that curling draws the magnetized end up away from the phone, rather than pushing down into the phone.

[0213] For simplicity, we begin with a bilayer comprising two layers of equal thickness. This will not always be true, in which case the full equation above can bereturned to, but starting with equal layer thicknesses significantly simplifies the above:13⋅^^ൌ^ ^^2^

[0214] Here we have also assumed equal Young's moduli for the two layers. Again, this is unlikely to be true but, as can be seen by substitution, even large differences in layer thicknesses or Young's moduli yield only small changes to the 3 / 2 prefactor.

[0215] Assuming homogeneous hydrogel material composition within each layer, and hence uniform hydrogel expansion along the length of the layers, the bilayer will always take the form of an arc of a circle with radius ^^ given above. (This remains true even for flat layers with ^^ ൌ 0, where the circle has effectively infinite radius). As ^^ increases with increasing analyte concentration, the curvature increases and the hydrogel strip conforms to an increasing tighter arc of an increasing smaller circle. The opening angle ^^ (in radians) of this arc formed by a bilayer of length ^^ is then: ^^ ൌ^^ 3 ^^^^ ൌ2 ⋅^^ℎ^ ^^3^

[0216] Examples of thefor various ^^ and overlaid for comparison on real world examples copied from FIG.19e- 19i.

[0217] Using the coordinate system sketched in FIG. 41 with the clamped end of the bilayer taken to be at the origin, the vector position of the magnetized particles at the free end of the strip becomes, quite generally, ^^^, ^^, ^^^ ൌ ^^ ⋅ ^sin ^^, 0,1 െ cos ^^^ ൌ ^^ ⋅ ^sin ^^^^ , 0,1 െ cos ^^^^ ൠ ^ ^^4^while the vector magnetization,is magnetized normal to its surface along its axis of rotation, points in the direction: ^^^^ ൌ ^^ ⋅ ^sin ^^, 0,െcos ^^^ ^ ^^5^

[0218] In the coordinate system (see FIG.41) with the surface of the phone at ^^ ൌ 0, the phone magnetometer, embedded a depth ^^^into the phone, lies at position ^ ^^, 0,െ ^^^^. The position of the magnetometer relative to the magnetized particles at the free end of the bilayer strip, can thus be described by a displacement vector:⇀^^ ൌ ^^ ⋅ ^1 െsin ^^ ^cos ^^ െ 1^ ^^^^^ , 0,^^ െ^^ ൠ ^ ^^6^which points from the magnetized particles towards the magnetometer and has length equal to the distance between the particles and the magnetometer.

[0219] For small deflections, ^^ remains small and substituting the Taylor expansions sin ^^ ^ ^^ and cos ^^ ^ 1 െ ^^ଶ / 2 into the above yields ^^ ൌ ^^ ⋅ ^ ^^, 0,െ1^ and ^^ ൌ ^0,0,െ ^^ ⋅ ^^ / 2 െ Z^^. That is, the magnetization continues to point primarily straight downwards towards the magnetometer and there is essentially zero motion in ^^ and ^^ with the magnetic particles being displaced primarily in the ^^-direction away from the magnetometer by a distance of ^^ ⋅ ^^ / 2. Taking ^^ ൌ 3 ^^ ⋅ ^^ / 2ℎ from above, the displacement thus scales not simply proportionally to ^^ ⋅ ^^, as would be true for a single homogeneous strip of hydrogel but instead proportionally to 3 ^^ ⋅ ^^ଶ / 4ℎ, which constitutes a key advantage in using a bilayer hydrogel strip to enhance measurement sensitivity.

[0220] For these small deflections, which proceed primarily vertically and without any significant reorientation of the magnetization, the field from the disk- shaped collection of magnetized particles takes a simple analytic form, given by Equation 1. For larger motions of the hydrogel bilayer, however, the magnetometer no longer continues to lie along the axis of the disk; nor does the disk magnetization ^^ point directly towards the magnetometer, invalidating the use of the simple on-axis circular current loop model used. At these larger distances, however, the field from the disk of particles can be well approximated with a simpler, spherical collection of particles, whose vector magnetic field ^^ at position ^^ relative to the center of that sphere is equivalent to that from a point magnetic dipole and given by: ⇀ ^⇀^^ ^^^^^^^3 ^ˆ^^ ^ˆ^ ⋅ ^^^ െ ^^^^^where ^^^is the vacuum unit displacement vector. Or, rewritten in terms of an actual sphere of finite radius ^^spherewith magnetization per unit volume, ^^ ൌ ^^ / ^ସ ଷଷ ^^ ^^sphere^ :⇀⇀ ^^ ଷ^ ^^^^^^^^ 3 ^ˆ^ ^ ^ˆ^ ⋅ ^^^ െ ^^^^^^dipole^ ^^^ ൌ^ ^ .

[0221] Substituting for the vectors ^^ and ^^ from Equations ^^5 and ^^6, then yields general expressions for all three vector components of the magnetic field at the location of the magnetometer that remain valid for arbitrarily large curlings of the hydrogel bilayer: sin ^^ଶ െ3sin ^^ cos ^^ െ 1 ^^ ଶ^ cos ^^ െ 1 ^^^^^^ ^^ ^^sଷphere^2sin ^^ ⋅ ^1 െ^^^cos ^^ ⋅ ^1 െ ^^ ^ ^ ^^ െ ^^ ^ െ sin ^^ ⋅ ^ ^^ െ ^^ ^ ^^^௫^ ^^^ ൌ⋅ଶ ^^in terms of the fractional hydrogel expansion ^^, which itself depends on the analyte concentration being tested, by substituting either the simple expression ^^ ൌ ^^ ⋅ ^3 ^^ / 2ℎ^, or by starting from the more complete expression in Equation S1, as appropriate.

[0223] While the above is valid for any ^^, it is instructive to compare its behavior for small ^^ with that for the diskshaped magnet given. Taylor expanding the above for small ^^ gives: ^^ ^^ ^^ଷ^^ ^ ^^^ ^ െ^ ^^^^^^ ^^

[0224] For field is Δ ^^ ൌ ^∂ ^^ / ∂ ^^^ ⋅ Δ ^^ which now in terms of ^^ becomes Δ ^^ ൌ ^∂ ^^ / ∂ ^^^ ⋅ ^∂ ^^ / ∂ ^^^ ⋅ Δ ^^. As shown above, for small ^^ the ^^-position of the magnet is described by ^^ ^ ^^ ⋅ ^^ / 2, giving ∂ ^^ / ∂ ^^ ൌ 2 / ^^. Taking Δ ^^ ൌ 3 ^^ ^^ଶ / 4ℎ, then yields:Δ ^^ ^ െ ^^ sଷ ^^௫ ^ ^^ ^^phere⋅ 2ℎ ^^ଷ⋅ ^^^^^

[0225] Toshaped magnets, the total magnetic moments of sphere and disk can be matched by equating their volumes via ^^sଷphereൌ 3 ^^ௗଶ^^^^^ / 4, where ^^ was the disk thickness. Note that in the limit ^^disk≪ ^^^, where point of the magnetometer the disk arrangement of magneticindistinguishable from a spherical one, Δ ^^௭becomes identically equivalent to that of Equation 2. Alternatively, setting ^^diskൌ^2 / 3 ⋅ ^^^, and substituting into the above yields: Δ^^^^ ^^ ^^௫^ െ^ ^^4ℎ ^^ ⋅ ^^^^^

[0226] As expected,form as Equation 3, only with a different numerical prefactor owing to the spherical, rather than disk-shaped, magnetic particle distribution. Interestingly, while the current work used a disk-shaped magnetic particle ensemble (because it was simplest to fabricate), comparing the above with Equation 3 shows that arranging the same quantity of magnetic particles into a sphere, rather than a disk, could in the future enhance sensor sensitivity a further 3-fold.

[0227] Range of validity of on-axis disk field model (Equation 1)

[0228] While the above gives general field expressions for arbitrary bilayer curling, the simpler on-axis disk field model can be applied over a large portion of the sensor's dynamic range, as shown here.

[0229] Equation 1, reproduced here for the field at a distance ^^ ^ ^^^away from the center of a magnetized disk of magnetization ^^, radius ^^, and thickness ^^, is given by: ^^ ^^ ^^ ଶ^^^ ^ ⋅ ^^^ ^

[0230] Substituting in the optimal disk radius, ^^ ൌ^2 / 3 ⋅ ^^^, gives: ^^ ^^ ^ ଶ^^ ^ ^^^ ൌ െ^ ^ ^^^௭^ ^^14^^^^ ^ ^2ଶଷ / ଶ^ which represents a field^^௭^ ^^^ falls to 1 / ^^ of its initial value, ^^௭^ ^^ ൌ 0^, when ^^ ൌ ^^^5 ^^ଶ / ଷെ 2^ / 3 െ 1^ ⋅ ^^^. For example, ^^௭^ ^^^ falls to one half of its initial value 0.4 ^^^above the surface of the phone. That is, for a^^^of around 3 to 5 mm beneath the surface of the phone, the field can be made to drop by 50% by raising the disk magnet's z-position just 1 to 2 mm above the phone surface. Assuming even a relatively short hydrogel bilayer strip with ^^ ൌ 20 mm, this corresponds to a change in orientation angle of the plane of the disk of order 5 to 10 degrees from horizontal and a shift in the magnet's x-position of no more than 0.1 mm, as can both be determined through use of Equation S4. At 0.1 mm, this lateral shift is both far smaller than the size of the magnetic disk and negligible compared to the disk's z- translation. Meanwhile, the 5-to-10-degree reorientation of the magnetization direction yields less than a 2 percent reduction in the ^^௭field component, which scales with the cosine of the reorientation angle. That is, over at least half of the sensor's dynamic range, the simple model of a disk translating purely vertically without any reorientation, as given in Equation 1, remains a good approximation.

[0231] Equivalent analysis shows that even a 75% field reduction still leads to a mostly negligible 0.5 mm lateral shift in position, albeit this time of order 20-degree reorientation corresponding to or order 10% decrease in the ^^ଶfield component. While still not a large error now over even a full 3 / 4 of the sensor dynamic range, good approximation can still be achieved with the horizontally oriented on-axis disk model of Equation 1 by adding a cos ^^ correction factor to better account for the (slightly) changed ^^௭field projection. Recasting Equation 1 then in terms of ^^, recalling that ^^ ൌ ^1 െ cos ^^^ ⋅ ^ ^^ / ^^^ from Equation S4, gives the more complex, but more accurate approximation:^^ ^^ ^^ ^^ଶ ^^ ^ ^^^ ൌ െ^ ^௭s ^^ 2ଷ / ⋅ cos ^^ ^ ^^15^െcoଶ ଶଶ

[0232] ^^௭field at the magnetometer directly in terms of the hydrogel fractional expansion, ^^ : ^^௭^ ^^^ ൌ െ^^^ ^^ ^^ ^^ଶ ^⋅ cos 3 ^^ ^^^^^16^^^ ଶ ଷ / ଶwhichunderstand this equation, the predicted ^^ଶfield at the location of a magnetometer embedded a distance ^^^ൌ 5 mm below the phone surface is shown plotted in FIG.43as a function of the hydrogel expansion ^^ for a typical hydrogel bilayer of length ^^ ൌ20 mm and thickness ℎ ൌ 0.5 mm. Focusing on the sensor's initial, most sensitive,measurement range, an overlaid straight line fit on the actual field shows that the sensor response deviates little from linearity over the first 50% of its dynamic range (see figure inset).

[0233] Comparison of bilayer vs monolayer

[0234] Comparing the above to that which would result from a monolayer gel, helps quantify the advantage of a bilayer hydrogel geometry. We perform this analysis here for monolayers oriented both horizontally (like the bilayer) and vertically above the phone surface, as shown schematically in FIG.44.

[0235] i) Horizontally oriented monolayer

[0236] If the above bilayer is replaced by a simple (monolayer) hydrogel, positioned identically to the bilayer above the phone and with a length that scales with the same fractional hydrogel expansion ^^ as the active layer in the above bilayer, then Equation S4 above can be rewritten for the position of the magnetized particles in a single layer system as: ^^^, ^^, ^^^ ൌ ^ ^^^1 ^ ^^^,0,0^ ^ ^^17^with the position of the magnetometer relative to the magnetized particles now being described by the displacement vector: ^^ ൌ ^െ ^^ ^^, 0,െ ^^^^ ^ ^^18^

[0237] Since expansion / contraction of a single homogeneous layer involves no change in curvature or angular orientation, Equation S5 for the vector magnetization, ^^, of the disk, simplifies to: ^^^^ ൌ ^^ ⋅ ^0,0,െ1^ ^ ^^19^

[0238] Substituting into Equation S8, then yields general expressions for the magnetic field at the location of the magnetometer, this time due to an expanding single hydrogel layer: ^^^^^ ^^sଷphe^^ ^^ ^^ ^re ^௫^^^ ൌ െ ^^ସ⋅ଶ ହ / ଶ which for small ^^^^ ^ଷ^^ ^^^ ^^^^^^^^௫^^^ ൌ െ⋅ ^^ ⋅ ^^ଶ^

[0239] For is Δ ^^ ൌ ^∂ ^^ / ∂ ^^^ ⋅ Δ ^^ which in terms of ^^ becomes Δ ^^ ൌ ^∂ ^^ / ∂ ^^^ ⋅ ^∂ ^^ / ∂ ^^^ ⋅ Δ ^^, where we have now switched from a motion that was primarily in the ^^-direction for a bilayer expansion to one that now proceeds in the ^^-direction for a single layer, simply expanding hydrogel. Substituting ∂ ^^ / ∂ ^^ ൌ 1 / ^^ and Δ ^^ ൌ ^^ ^^, then yields:௫^^^^ ^^sଷ^^ Δ ^^ ^ െ ^phere⋅ ^^ସ⋅ ^^^ ^^ଶ

[0240] Whereasoccurs primarily in ^^௭, for a monolayer oriented identically to a (initially flat) bilayer, the field change occurs primarily in ^^^. Comparing this field change to that of an equivalent bilayer system (see Equation S11) shows that for the same hydrogel expansion, the bilayer system yields a field change that is larger than that of an equivalently oriented and positionedmonolayer system by a factor of ^3 / 2^ ⋅ ^ ^^ / ℎ^. That is, for a typical bilayer with ^^ ൌ20 mm and ℎ ൌ 0.5 mm, the bilayer yields nearly two orders of magnitude greatersensitivity, with this relative advantage increasing for longer and / or thinner bilayer strips.

[0241] ii) Vertically oriented monolayer

[0242] A monolayer system could also alternatively be oriented vertically, rather than laying horizontally, on the phone surface as analyzed above. In this case Equation S4 for the position of the magnetized particles becomes: ^ ^^, ^^, ^^^ ൌ ^ ^^, 0, ^^^1 ^ ^^^^ ^ ^^23^ with the position of the magnetometer relative to the magnetized particles now being described by the displacement vector: ^^ ^0,0,െ ^^^െ ^^^1 ^ ^^^^ ^ ^^24^

[0243] Regardless of whether the monolayer is oriented horizontally or vertically, the vector magnetization, ^^, of the disk remains: ^^^^ ൌ ^^ ⋅ ^0,0,െ1^ ^ ^^25^

[0244] Substituting magnetic field at the location of the magnetometer, this time due to an expanding single hydrogel layer that is vertically oriented:^^௫^ ^^^ ൌ 0 ^^ ଷ^^ ^ ^^^ ൌ െ^ ^^ ^^sphere 2⋅which for small ^^^^௫^ ^^^ ൌ 0 ^^ ଷ^^ ^ ^^^^ ^^ ^^sphere ⋅ 6 ^^ ^^

[0245] For⋅ Δ ^^, or in terms of ^^,Δ ^^ ൌ ^∂ ^^ / ∂ ^^^ ⋅ ^∂ ^^ / ∂ ^^^ ⋅ Δ ^^. Substituting ∂ ^^ / ∂ ^^ ൌ 1 / ^^ and Δ ^^ ൌ ^^ ^^, then yields: Δ ^^௫ൌ 0 ଷ 2 ^^ ^ ^^ ⋅⋅ ^^

[0246] an equivalent bilayer system (see Equation S11) shows that for the same hydrogel expansion, a bilayer system yields a field change that is larger than that of an equivalently sized, vertically oriented monolayer system by a factor of ^3 / 4^ ⋅ ^1 ^ ^^ / ^^^^ସ⋅ ^ ^^ / ℎ^. For example, for the same typical bilayer with ^^ ൌ 20 mm and ℎ ൌ 0.5 mm, the bilayer yields over four orders of magnitude greater sensitivity. These results are summarized in FIG.44. Table 1: Cost estimate for glucose Hydrogel Actuator (cost per individual hydrogel actuator) Component Glucose Smart Hydrogel Inert Hydrogel Acrylamide 0.06$ 0.28$ ത^ത^ത^ത^ ^ത^ 0.01$ 0.03ΦDMA 0.04$ 0.08$ 3 െ APB 13.24Φ N / ALAP 0.53$ 1.76Φ Total cost of above monomers 13.88Φ 2.15Φ NdଶFe^ସB 0.04$ Total: $0.16 Table 2: Cost estimate for pH Hydrogel Actuator Cost per individual hydrogel actuator Inert Hydrogel Component pH Smart Hydrogel 0.21Φ Acrylamide 0.13Φ N / A Acrylic Acid 0.04Φ 0.20Φ Poly(ethylene glycol) diacrylate, 1.07Φ 0.04Φ average molecular weight 700 2,2-Dimethoxy-2- 0.20Φ phenylacetophenone Total cost of above monomers 2.44Φ 0.45Φ Nd 2Fee^ସB 0.04Φ Total: $0.03

[0247] Synthesis of Glucose Hydrogel Actuators. A ' ^^ ' shaped poly- dimethylsiloxane (PDMS) well was first created and then used as a mold to form the glucose hydrogel actuators. The top, horizontal segment was 12 mm in width, 4 mmin height, and 0.5 mm in depth and the bottom, vertical segment was 10 mm in height,4 mm in width, and 0.5 mm in depth. Corners were rounded to reduce any potentialstress buildup in the hydrogel shape. A thin, 0.05 mm tall bar protruding from the bottom of the well was used to separate the horizontal segment from the vertical segment.24 mL of inert hydrogel precursor was placed in the top, horizontal segment of the well and pinned to the walls of the well and the separating bar via naturally occurring capillary wetting forces.20 mL of glucoseresponsive precursor was spread on the vertical segment and similarly pinned to the walls and gently connected to the inert precursor in the horizontal segment. The bottom layer was then partially cured under UV light ( 365 nm, 4 W ) with Nଶgas flowing for 40 seconds. Then, 2mg of silica- coated NdଶFe^ସB particles were mixed into 22 mL of inert precursor and deposited on top of an immobilized magnet, placed directly beneath the PDMS well, to magnetically attract the particles into a disc shape near the tip of the vertical arm, before spreading the liquid inert precursor to the walls of the well along the T-shape. Due to shrinkage of the bottom layer during curing, the same well walls were used to pin both the topand bottom layers. Both layers were then fully cured and bonded under UV light (365 nm, 4 W ) with Nଶ gas flowing for 10 minutes.

[0248] Synthesis of pH Hydrogel Actuators. A similar 'T'-shaped PDMS well was used to form the pH hydrogel actuators. The top, horizontal segment was 16.5 mmin width, 5.5 mm in height, and 0.5 mm in depth and the bottom, vertical segment was15 mm in height, 5.5 mm in width, and 0.5 mm in depth. Corners were rounded toreduce any potential stress buildup in the hydrogel shape. Due to a difference in degree of initial swelling when placed in solution after curing, pH hydrogel actuators were synthesized in larger wells to achieve similar sized structures to the glucose counterparts.110 mL of inert hydrogel was placed in the well and pinned to all edges of the ' T ' shape before partially curing under UV light ( 365 nm, 4 W ) with Nଶgasflowing for 20 seconds. Then, 2mg of silica coated NdଶFe^ସ B particles were mixed into10 mL of pH hydrogel precursor and deposited on top of an immobilized magnet,placed directly beneath the PDMS well, to magnetically attract the particles into a disc shape near the tip of the vertical arm, before pinning the pH hydrogel precursor to theedges along the vertical segment of the well only. Both layers were then fully cured and bonded under UV light ( 365 nm, 4 W ) with Nଶgas flowing for 5 minutes.

[0249] Smartphone data collection. Two smartphones were typically used for data collection; one with the sensor platform attached (sensor phone) and a second smartphone that was placed near nearby and with no attachments to control for potential variations in background magnetic field (background phone). Magnetometer data was collected on both the sensor phone and background phone using Physics Toolbox Pro app for all experiments, with initial calibration to subtract off Earth's background field. All other apps, internet, Bluetooth, and other phone functions were turned off during testing to prevent CPU usage from affecting the magnetometer readings^. A background-subtracted ^^௧was then determined with the formula ^^௧ൌ^^^௫ଶ^ ^^௬ଶ^ ^^௭ଶ, where ^^௫, ^^௬, and ^^௭are the background-subtracted field readings (sensor phone reading minus control phone reading) in the ^^, ^^, and ^^ directions. Although background subtraction was always performed, it was found empirically to almost never be needed, not making any significant difference to the data unless there was a significant external magnetic event during data collection (which happened only rarely and only when doing very long runs over many hours).

[0250] Detection Limit Testing. A single glucose hydrogel actuator was used to collect the data shown in FIG.21A. For each experiment, the hydrogel actuator was given four hours to equilibrate in 5 mL of HEPES / NaOH buffer, pH7.4, with 0mM glucose. Then, a small amount of HEPES / NaOH buffer, pH7.4, with 2mM glucose was added to the test solution ( 12.5 mL, 18.8 mL, 25.1, or 50.4 mL ) to raise the total glucose concentration to the desired levels ( 5mM, 7.5mM, 10mM or 20mM, respectively), followed by gently mixing the solution with a 2 mL transfer pipette to achieve a uniform glucose concentration throughout. To control for the effects of the injecting and mixing process, 50.4 mL of HEPES / NaOH buffer, pH7.4, with 0mM glucose was added to the solution, followed by the same mixing procedure. Each glucose concentration and the control were tested in triplicate and in random order, and the average is shown in FIG.22b. A 60 second moving average was applied to the data sets, and Δ ^^௭is calculated from a baseline of the field strength reading at 3.5 minutes to provide time for the actuator to settle after the injection and mixing process.

[0251] The processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more general purpose computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may alternatively be embodied in specialized computer hardware. In addition, the components referred to herein may be implemented in hardware, software, firmware, or a combination thereof.

[0252] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi- threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0253] Any logical blocks, modules, and algorithm elements described or used in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and elements have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions cannot be interpreted as causing a departure from the scope of the disclosure.

[0254] The various illustrative logical blocks and modules described or used in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processing unit or processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gateor transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computer-executable instructions. In another embodiment, a processor includes an FPGA or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0255] The elements of a method, process, or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non- transitory computer-readable storage medium, media, or physical computer storage known in the art. An example storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The storage medium can be volatile or nonvolatile.

[0256] While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the presentinvention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.

[0257] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like.

[0258] As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.

[0259] All references are incorporated herein by reference.

[0260] The use of the terms “a,” “an,” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements cannot be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such.

[0261] The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances. / / PARTS LIST / / analyte flexure sensor 100 flexural member 101 primary region 102 secondary region 103 magnetic material 104 magnetic field sensitive transducer 105 / / magnetometer 105 readout interface 106 / / smartphone 106 flexural motion 107 analyte composition 108 analyte composition container 109 immobilization member 110 attachment and alignment device 111 tertiary region 112 sensing an analyte

Claims

What is claimed is:

1. An analyte flexure sensor (100), comprising: a flexural member (101) comprising a primary region (102) attached to a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with an analyte composition (108) that contains an analyte to a different extent from that of secondary region (103); magnetic material (104) disposed in or on flexural member (101); a magnetic field sensitive transducer (105) disposed proximate to the freely translating region of flexural member (101) in analyte composition container (109), wherein magnetic field sensitive transducer (105) produces an output signal that changes in response to translation of the freely translating region of flexural member (101); and a readout interface (106) configured to receive the output signal from magnetic field sensitive transducer (105).

2. The analyte flexure sensor (100) of claim 1, further comprising: an analyte composition container (109) for receiving analyte composition (108) and comprising an immobilization member (110) configured to constrain motion of a point, edge, or area of flexural member (101) while another region of flexural member (101) translates freely through space.

3. The analyte flexure sensor (100) of claim 1, wherein primary region (102) expands or contracts in response to contact with the analyte composition (108) and secondary region (103) does not.

4. The analyte flexure sensor (100) of claim 1, wherein the flexural member (101) comprises a bilayer structure, wherein primary region (102) is a first layer and secondary region (103) is a second layer of the bilayer structure.

5. The analyte flexure sensor (100) of claim 3, wherein the first layer and the second layer are attached by covalent bonding.

6. The analyte flexure sensor (100) of claim 3, wherein at least one of the first layer or the second layer comprises a hydrogel.

7. The analyte flexure sensor (100) of claim 1, wherein primary region (102) and secondary region (103) are integral and comprise a gradient in material composition extending from primary region (102) to secondary region (103).

8. The analyte flexure sensor (100) of claim 1, wherein the magnetic material (104) is disposed in the freely translating region of flexural member (101).

9. The analyte flexure sensor (100) of claim 1, wherein the magnetic material (104) includes a plurality of magnetic particles embedded in flexural member (101).

10. The analyte flexure sensor (100) of claim 1, wherein the magnetic field sensitive transducer (105) includes a magnetometer.

11. The analyte flexure sensor (100) of claim 1, wherein the readout interface (106) includes a smartphone.

12. A process for sensing an analyte with an analyte flexure sensor (100), the process comprising: contacting a flexural member (101) with an analyte composition (108) that contains an analyte, the flexural member (101) comprising a primary region (102) attached to a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with the analyte composition (108) to a different extent from that of secondary region (103), and further wherein the flexural member (101) has a first region that is constrained from motion and a second region that translates freely through space; detecting a change in a magnetic field (104) proximate to the freely translating second region of flexural member (101) with a magnetic field sensitive transducer (105) in response to the freely translating second region of flexural member (101) undergoing translation; and receiving an output signal from the magnetic field sensitive transducer (105) in a readout interface (106).

13. The process of claim 11, wherein the change in the magnetic field (104) is a decrease in magnetic field strength.

14. The process of claim 11, further comprising determining a concentration of the chosen analyte in the analyte composition (108) based on the output signal from the magnetic field sensitive transducer (105).

15. The process of claim 13, wherein the determining comprises correlating the output signal with a concentration of the chosen analyte based on prior calibration of the analyte flexure sensor (100).

16. The process of claim 11, wherein primary region (102) expands or contracts in response to contact with the analyte composition (108) and secondary region (103) does not.

17. The process of claim 11, wherein the flexural member (101) comprises a bilayer structure, wherein primary region (102) is a first layer and secondary region (103) is a second layer of the bilayer structure.

18. The process of claim 16, wherein the first layer and the second layer are attached by covalent bonding.

19. The process of claim 16, wherein at least one of the first layer or the second layer comprises a hydrogel.

20. The process of claim 11, wherein primary region (102) and secondary region (103) are integral and comprise a gradient in material composition extending from primary region (102) to secondary region (103).

21. The process of claim 11, wherein the contacting comprises disposing the flexural member (101) in an analyte composition container (109), and further wherein an immobilization member (110) in the analyte composition container (109) constrains the flexural member (101) from motion at the first region.

22. A process for making an analyte flexure sensor (100), the process comprising:providing a flexural member (101) comprising a primary region (102) and a secondary region (103), wherein primary region (102) is of a material composition that expands or contracts in response to contact with an analyte composition (108) that contains an analyte to a different extent from that of secondary region (103); disposing magnetic material (104) in or on the flexural member (101); and disposing the flexural member (101) in an analyte composition container (109) comprising an immobilization member (110) configured to constrain motion of a point, edge, or area of the flexural member (101).

23. The process of claim 21, wherein the providing comprises: forming a first layer comprising the primary region (102); forming a second layer comprising the secondary region (103); and attaching the first layer to the second layer to form the flexural member (101).

24. The process of claim 22, wherein the attaching comprises covalently bonding the first layer to the second layer.

25. The process of claim 22, wherein at least one of the first layer or the second layer comprises a hydrogel.

26. The process of claim 24, wherein forming the hydrogel comprises crosslinking a polymer network.

27. The process of claim 21, wherein the providing comprises forming the flexural member (101) with a gradient in material composition that extends from the primary region (102) to the secondary region (103).

28. The process of claim 21, wherein the disposing of the magnetic material (104) comprises embedding a plurality of magnetic particles in the flexural member (101).

29. The process of claim 27, further comprising magnetizing the magnetic particles.

30. The process of claim 28, wherein the magnetizing comprises exposing the magnetic particles to a magnetic field.

31. The process of claim 21, wherein the immobilization member (110) is configured to constrain motion of an end of the flexural member (101).

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