Solid-state substrate integrated reference and counter electrodes

Abstract

Aspects relate to a reference electrode integrated on a surface of a substrate to facilitate functionalization of a working electrode. The reference electrode is used for electrochemical deposition or electrodeposition of one or more functional layers on the working electrode. The working electrode can be a sensing element of an analyte-selective sensor. Further aspects of the current subject matter relate to a counter electrode integrated on a surface of a substrate.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 121,223, filed December 3, 2020, entitled “Solid-State Substrate-Integrated Reference Electrodes Providing for Functional Layer Electrodeposition and Methods for the Realization of Same,” the contents of which are incorporated herein by reference in their entirety. Background Technology

[0003] Electrochemical deposition involves a method of depositing a sensing layer on a sensing element. To achieve electrochemical deposition of the sensing layer, a stable reference is required. This stable reference can take the form of a reference electrode that provides a stable electrode voltage to facilitate electrochemical deposition within an electrolytic cell. Summary of the Invention

[0004] One aspect of the current subject matter relates to a reference electrode integrated on the surface of a substrate to facilitate the functionalization of the working electrode. Another aspect of the current subject matter relates to a counter electrode integrated on the surface of a substrate.

[0005] A aspect of the present subject relates to an apparatus comprising a substrate, a reference electrode, and a working electrode, wherein the reference electrode and the working electrode form an electrolytic cell in a fluid medium, and wherein applying an electrical stimulus to the working electrode in the electrolytic cell provides electrodeposition of an upper surface layer of the working electrode. In some embodiments, the working electrode is positioned on a front surface of the substrate. In some embodiments, the reference electrode includes a transducer positioned on the front surface of the substrate and a capping layer comprising a redox pair applied to a first surface of the transducer. In some embodiments, the redox pair includes Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2. In some embodiments, the redox pair facilitates the formation of a stable electrode potential optionally between -1.5 volts and +1.5 volts relative to a standard hydrogen electrode. In some embodiments, the apparatus is an analyte-selective sensor, and the working electrode includes a sensing element.

[0006] In some embodiments, the surface layer of the working electrode comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion confinement layer, a biocompatible layer, and an interference suppression layer. In some embodiments, the working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors, and polymers. In some embodiments, the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices. In some embodiments, the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors. In some embodiments, the transducer comprises at least one selected from the group consisting of metals, metal alloys, and metal oxides. In some embodiments, the capping layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metallic inks, metallic pastes, semiconductors, and conductive polymers.

[0007] In some embodiments, the application of the electrical stimulation comprises one or more selected from the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and potentiochemical current application. In some embodiments, the electrolytic cell includes a counter electrode. In some embodiments, the fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents, or dispersions.

[0008] An aspect of the present subject relates to a method comprising: providing an apparatus including a substrate, a reference electrode, and a working electrode, wherein the reference electrode and the working electrode are positioned on a front surface of the substrate and form an electrolytic cell in a fluid medium, and wherein the reference electrode includes a transducer positioned on the front surface of the substrate and a capping layer including a redox pair applied to a first surface of the transducer; immersing the apparatus in the fluid medium; and applying an electrical stimulus to the working electrode to induce electrodeposition of the surface layer on the working electrode. In some embodiments, the redox pair includes Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2. In some embodiments, the redox pair promotes the formation of a stable electrode potential. In some embodiments, the stable electrode potential is between -1.5 volts and +1.5 volts relative to a standard hydrogen electrode. In some embodiments, the working electrode is a sensing element in an analyte-selective sensor.

[0009] In some embodiments, the surface layer comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion confinement layer, a biocompatible layer, and an interference suppression layer. In some embodiments, the working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors, and polymers. In some embodiments, the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices. In some embodiments, the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors. In some embodiments, the transducer comprises at least one selected from the group consisting of metals, metal alloys, and metal oxides. In some embodiments, the capping layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metallic inks, metallic pastes, semiconductors, and conductive polymers.

[0010] In some embodiments, the application of the electrical stimulation comprises one or more selected from the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and potentiochemical current application. In some embodiments, the electrolytic cell includes a counter electrode. In some embodiments, the fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents, and dispersions.

[0011] The foregoing general description and the following detailed description are exemplary and illustrative only, and not restrictive. Further features and / or variations may be provided in addition to those set forth herein. For example, the implementations described herein may involve various combinations and sub-combinations of the disclosed features. Attached Figure Description

[0012] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate certain aspects of the subject matter disclosed herein and, together with the description, help to explain some principles associated with the disclosed implementations. In the drawings,

[0013] Figure 1 An exemplary schematic diagram depicting a substrate with an integrated reference electrode according to an implementation of the present topic;

[0014] Figure 2 An exemplary schematic diagram depicting a substrate with an integrated reference electrode according to an implementation of the present topic;

[0015] Figure 3 An exemplary schematic diagram depicting a substrate with an electrolytic cell according to an implementation of the present subject;

[0016] Figure 4 An exemplary schematic diagram depicts a substrate having an integrated reference electrode and an integrated counter electrode, according to an implementation of the present subject.

[0017] Figure 5 An exemplary schematic diagram depicts a substrate having an integrated reference electrode and an integrated counter electrode, according to an implementation of the present subject matter; and

[0018] Figure 6A An exemplary schematic diagram depicting a microneedle array, and Figure 6B Depicting Figure 6A An exemplary schematic diagram of the microneedles in the microneedle array depicted in the figure. Detailed Implementation

[0019] One aspect of the present subject matter relates to a reference electrode integrated on the surface of a substrate to facilitate the functionalization of a working electrode. According to the implementation of the present subject matter, the reference electrode is used for the electrochemical deposition (also known as electrodeposition) of one or more functional layers on the working electrode. The working electrode can be, for example, a sensing element of an analyte-selective sensor. Another aspect of the present subject matter relates to a counter electrode integrated on the surface of a substrate.

[0020] In the implementation of analyte-selective sensors, one or more analyte-selective layers need to be deposited on the working electrode used as the sensing element. Electrodeposition is a method that provides uniformity of the analyte-selective layer and allows for high-precision control of the amount of deposited material. To achieve the electrodeposition of one or more sensing layers, a stable reference is required. This stable reference can take the form of a reference electrode.

[0021] In conventional systems or applications, a reference electrode may be, for example, a metal wire immersed in an internal filling solution and containing a liquid junction. While this implementation may be feasible in scientific and laboratory settings, there are challenges in extending the use of liquid-junction reference electrodes to highly parallelized industrial processes. In such applications, a reference electrode architecture that eliminates the need for external devices to impart the stable electrode voltage required for the electrolytic reaction would enable the highly parallel synthesis of analyte-selective sensors in commercial environments.

[0022] Therefore, an aspect of the present subject provides a solid-state reference electrode integrated on the surface of a substrate in contact with fluids in an electrolytic cell for facilitating the electrochemical synthesis of one or more functional layers on a working electrode located within the electrolytic cell.

[0023] Electrochemical deposition is a technique for depositing films of conductive chemical substances dissolved in a bulk solution. In this process, the chemical substance undergoes a reduction or oxidation reaction and is thus deposited as a film at the cathode or anode, respectively, during electrolysis under a given bias. To drive the redox reaction at a defined and controllable rate, a specific potential must be established at the anode or cathode, which will induce current flow between the two electrodes. To prevent the possibility of a large ohmic drop due to current flow in the finite-resistivity electrolyte (which could cause the potential to deviate from the expected value), a third electrode, a reference electrode, is provided, from which a stable potential is referenced relative to the anode or cathode. The function of the reference electrode is to provide a thermodynamically stable electrode potential, whose performance characteristics do not change perceptibly under varying test conditions, thereby referencing the electrolytic reaction. The reference electrode does not participate in the electron transfer reaction occurring between the anode and cathode (e.g., operating at zero current), and the reference electrode itself employs a reversible redox pair to establish a stable and well-characterized electrode potential. This requires a semi-sealed system containing the redox pair, immersed or dispersed in a liquid or aqueous solution, and a manner that promotes ohmic contact with the bulk solution. The reference electrode establishes the half-cell composition required to construct a stable electrochemical cell.

[0024] The present subject provides a solid-state reference electrode directly integrated onto a substrate, thereby forming an integrated reference electrode. The integrated reference electrode is formed through an electrodeposition process of a functional layer on one or more working electrodes. In some variations, the integrated reference electrode is intended for use only during the electrodeposition process.

[0025] In some variations, the implementation of a solid-state substrate integrated reference electrode allows for the electrodeposition of a functional layer (e.g., a surface immobilization layer) onto at least one working electrode located within an anatomical selective sensor to be applied to an anatomical structure (e.g., the human body). The solid-state substrate integrated reference electrode enables the synthesis of anatomical selective sensors in a highly parallelized manner, thereby eliminating the need for precision and bulky liquid-bonded reference electrodes.

[0026] In some variations, the integrated reference electrode is located on the surface of a printed circuit board. In some variations, the integrated reference electrode is located on the surface of a flexible circuit board. In some variations, the integrated reference electrode is located on the surface of a semiconductor device (e.g., an integrated circuit or a microelectromechanical system (MEMS)).

[0027] In some variations, the integrated reference electrode includes a transducer layer and a redox-active capping layer located on the front surface of the substrate. The redox-active capping layer includes a redox pair having a known and stable electrode potential.

[0028] The reference electrode, immersed in the same solution as the working electrode and optional counter electrode, forms the electrolytic cell together with the working electrode and optional counter electrode. The integrated reference electrode provides simplified parallelization of batch electrolysis or electrodeposition processes, is easily scalable to high-volume manufacturing, and reduces the cost of bulky components and their maintenance.

[0029] In some variations, the reference electrode assembly includes a substrate, a transducer, and a coating containing a redox pair applied to the front surface of the transducer. The reference electrode serves as a component of the electrolytic cell and is configured to operate in the same fluid medium as the working electrode.

[0030] Figure 1 An exemplary schematic diagram depicts an apparatus 100 including a substrate 110 with an integrated reference electrode 120, according to an implementation of the present subject matter. The apparatus 100 also includes a plurality of electrodes 130 including one or more working electrodes 135. The integrated reference electrode 120 and the plurality of electrodes 130 are positioned on the front surface of the substrate 110. Figure 2 Describing something similar to Figure 1 An exemplary schematic diagram of the device 100 and the device 200. An integrated reference electrode 120 and a plurality of electrodes 130, including one or more working electrodes 135, are positioned on the front surface of the substrate 110.

[0031] refer to Figure 1 The device 100 shown in the figure and Figure 2 The device 200 is shown in the figure. The number of the plurality of electrodes 130 is not limited to a specific value, and any number of electrodes 130 can be incorporated. Device 100 includes seven electrodes 130, and device 200 includes 37 electrodes 130. In other variations, any number of electrodes can be incorporated. Furthermore, the configuration of the plurality of electrodes 130 is not limited to a specific arrangement, and the plurality of electrodes 130 can be arranged in various types of configurations. For example, substrate 110 may have a generally flat surface. In some variations, the working electrode 135 may be formed as a microneedle protruding from the surface of substrate 110 or included in said microneedle. In some variations, the microneedle including the working electrode 135 may be as follows: Figure 6A and Figure 6B The configuration shown is described below with respect to microneedle 510. In some variations, the working electrode 135 may be located on the surface of the distal tapered portion of the microneedle, as described below. Figure 6A and Figure 6B Electrode 520 is shown in the figure. In some variations, reference electrode 120 may have a flat surface that is substantially parallel to the surface of substrate 110. In some variations, the surface of reference electrode 120 may be flush with or recessed relative to the surface of substrate 110.

[0032] Figure 3An exemplary schematic diagram depicts an apparatus 300 having a substrate 110 and an electrolytic cell 310 according to an implementation of the present subject matter. A reference electrode 120 is formed from a transducer 320 having a capping layer 330. In some variations, the capping layer 330 includes a redox pair applied to a first (e.g., top) surface of the transducer 320. A working electrode 135, together with the reference electrode 120, forms the electrolytic cell 310 in a fluid medium (not shown). According to aspects of the present subject matter, applying electrical stimulation to the working electrode 135 results in the electrodeposition of a surface layer 340 on the exposed surface of the working electrode 135. In some variations, the surface layer 340, also referred to as a surface immobilization layer, is one or more of a functional layer, thin film, membrane, sensing layer, biometric layer, diffusion-limiting layer, biocompatible layer, and interference-suppressing layer.

[0033] like Figure 3 As shown, the electrolytic cell 310 positioned on the substrate 110 includes a transducer 320, a working electrode 135, and a capping layer 330 and a surface layer 340 having embedded redox pairs.

[0034] Figure 4 and Figure 5 Devices 400 and 500 are depicted, each having an integrated reference electrode 120 and a plurality of electrodes 130 including one or more working electrodes 135. Devices 400 and 500 also include a counter electrode 410, also referred to as an auxiliary electrode. The number of the plurality of electrodes 130 is not limited to a specific value and any number of electrodes 130 can be incorporated. Device 100 includes seven electrodes 130, and device 200 includes 37 electrodes 130. In other variations, any number of electrodes can be incorporated. Furthermore, the configuration of the plurality of electrodes 130 is not limited to a specific arrangement, and the plurality of electrodes 130 can be arranged in various types of configurations. For example, substrate 110 may have a generally flat surface. In some variations, the working electrode 135 may be formed as a microneedle protruding from the surface of substrate 110 or included in said microneedle. In some variations, the microneedle including the working electrode 135 may be as follows: Figure 6A and Figure 6B The configuration shown is described below with respect to microneedle 510. In some variations, the working electrode 135 may be located on the surface of the distal tapered portion of the microneedle, as described below. Figure 6A and Figure 6B Electrode 520 is shown in the figure. In some variations, reference electrode 120 and / or counter electrode 410 may have a flat surface that is substantially parallel to the surface of substrate 110. In some variations, the surface of reference electrode 120 and / or counter electrode 410 may be flush with or recessed relative to the surface of substrate 110.

[0035] The counter electrode 410 is used to supply (provide) or absorb (accumulate) electrons by means of current, said electrons being necessary to sustain the electrochemical reaction at the working electrode. To handle the current, the counter electrode 410 must have sufficient size. In some variations, the counter electrode 410 is approximately ten times the size of the working electrode. In some variations, the counter electrode 410 is between five and fifteen times the size of the working electrode. In some variations, the counter electrode 410 is approximately five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen, or fifteen times the size of the working electrode. In some variations, the size of the counter electrode relative to the working electrode refers to the surface area of ​​the corresponding electrode.

[0036] Figure 6A A microneedle array 600 is depicted therein, which enables the current subject to be realized. The microneedle array 600 for sensing one or more analytes may include one or more microneedles 510 protruding from a substrate surface 502. For example, the substrate surface 502 may be generally flat. The one or more microneedles 510 may protrude orthogonally from the flat surface. Generally speaking, as... Figure 6B As shown, microneedle 510 may include a body portion 512 (e.g., a shaft) and a tapered distal portion 514 configured to pierce a user's skin. In some variations, the tapered distal portion 514 may terminate at an insulated distal apex 516. Microneedle 510 may also include an electrode 520 located on the surface of the tapered distal portion. In some variations, electrode-based measurements may be performed at the junction of the electrode and interstitial fluid located in the body (e.g., across the entire outer surface of the microneedle). In some variations, microneedle 510 may have a solid core (e.g., a solid body portion), but in some variations, microneedle 510 may include one or more lumens, for example, for drug delivery or sampling of dermal interstitial fluid. Other microneedle variations may similarly include a solid core or one or more lumens.

[0037] The microneedle array 600 may be at least partially formed from a semiconductor (e.g., silicon) substrate and includes various material layers applied and shaped using various suitable microelectromechanical systems (MEMS) fabrication techniques (e.g., deposition and etching techniques), as further described below. The microneedle array can be reflow soldered to a circuit board similar to a typical integrated circuit. Furthermore, in some variations, the microneedle array 600 may include a three-electrode arrangement including a working (sensing) electrode, a reference electrode, and a counter electrode, having an electrochemical sensing coating (including biorecognition elements such as enzymes) capable of detecting target analytes. In other words, the microneedle array 600 may include at least one microneedle 510 including a working electrode, at least one microneedle 510 including a reference electrode, and at least one microneedle 510 including a counter electrode. Further details of these types of electrodes are described in more detail below.

[0038] In some variations, the microneedle array 600 may include a plurality of microneedles that are insulated, such that the electrode on each of the plurality of microneedles is individually addressable and electrically isolated from each other electrode on the microneedle array. The resulting individual addressability of the microneedle array 600 allows for better control over the function of each electrode, as each electrode can be probed individually. For example, the microneedle array 600 can be used to provide multiple independent measurements of a given target analyte, which improves the sensing reliability and accuracy of the device. Furthermore, in some variations, the electrodes of the plurality of microneedles may be electrically connected to generate an increased signal level. As another example, the same microneedle array 600 may be additionally or alternatively interrogated to simultaneously measure multiple analytes to provide a more comprehensive assessment of physiological status. For example, the microneedle array may include a portion of microneedles for detecting a first analyte A, a second portion of microneedles for detecting a second analyte B, and a third portion of microneedles for detecting a third analyte C. The microneedle array can be configured to detect any suitable number of analytes (e.g., 1, 2, 3, 4, 5, or more). For example, suitable target analytes for detection may include glucose, ketones, lactates, and cortisol. Therefore, the individual electrical addressing capability of the microneedle array 600 provides greater control and flexibility in the sensing function of the analyte monitoring device.

[0039] In some variations of the microneedle (e.g., microneedles with a working electrode), electrode 520 may be located proximal to the insulating distal vertex 516 of the microneedle. In other words, in some variations, electrode 520 does not cover the vertex of the microneedle. Instead, electrode 520 may be offset from the vertex or tip of the microneedle. The proximity or offset of electrode 520 from the insulating distal vertex 516 of the microneedle advantageously provides more accurate sensor measurements. For example, this arrangement prevents the electric field from concentrating at the microneedle vertex 516 during the manufacturing process, thereby avoiding uneven electrodeposition of sensing chemicals on the electrode surface 520 that could lead to false sensing.

[0040] As another example, positioning electrode 520 offset from the microneedle apex further improves sensing accuracy by reducing unwanted signal artifacts and / or erroneous sensor readings caused by pressure during microneedle insertion. The distal apex of the microneedle is the first area penetrated into the skin and therefore experiences the greatest stress due to mechanical shearing phenomena accompanying skin tearing or cutting. If electrode 520 is placed at the apex or tip of the microneedle, this mechanical stress can cause delamination of the electrochemical sensing coating on the electrode surface and / or result in the delivery of small but disruptive tissues to the active sensing portion of the electrode. Therefore, positioning electrode 520 sufficiently offset from the microneedle apex improves sensing accuracy. For example, in some variations, the distal edge of electrode 520 may be located at least about 10 μm (e.g., between about 20 μm and about 30 μm) from the distal apex or tip of the microneedle, as measured along the longitudinal axis of the microneedle.

[0041] The body portion 512 of the microneedle 510 may also include a conductive path extending between the electrode 520 and a back electrode or other electrical contact (e.g., disposed on the back side of the substrate of the microneedle array). The back electrode may be soldered to a circuit board, thereby enabling electrical communication with the electrode 520 via the conductive path. For example, during use, an in vivo sensed current (inside the dermis) measured at the working electrode is interrogated by the back electrical contact, and an electrical connection between the back electrical contact and the working electrode is facilitated by the conductive path. In some variations, this conductive path may be facilitated by a metal via through the interior of the microneedle body portion (e.g., shaft) between the proximal and distal ends of the microneedle. Alternatively, in some variations, the conductive path may be provided through the entire body portion formed of a conductive material (e.g., doped silicon). In some of these variations, the entire substrate on which the microneedle array 600 is constructed may be conductive, and each microneedle 510 in the microneedle array 600 may be electrically isolated from adjacent microneedles 510, as described below. For example, in some variations, each microneedle 510 in the microneedle array 600 may be electrically isolated from adjacent microneedles 510 by an insulating barrier comprising an electrically insulating material (e.g., a dielectric material, such as silicon dioxide) surrounding a conductive path extending between the electrode 520 and the back electrical contact. For example, the body portion 512 may include an insulating material forming a sheath around the conductive path, thereby preventing electrical communication between the conductive path and the substrate. Other exemplary variations of the structure for achieving electrical isolation between microneedles are described in further detail below.

[0042] This electrical isolation between the microneedles in the microneedle array allows for individual addressability of the sensors. This individual addressability advantageously enables independent and parallel measurements between sensors, as well as dynamic reconfiguration of sensor assignments (e.g., assignment to different analytes). In some variations, the electrodes in the microneedle array can be configured to provide redundant analyte measurements, an advantage over conventional analyte monitoring devices. For example, redundancy can improve device performance by increasing accuracy (e.g., averaging multiple analyte measurements for the same analyte, which reduces the impact of extremely high or low sensor signals on analyte level determination) and / or by reducing the likelihood of overall failure.

[0043] In some variations, microneedle arrays can be formed, at least in part, using suitable semiconductor and / or MEMS fabrication techniques and / or mechanical cutting or dicing. For example, such processes can facilitate the large-scale, cost-effective fabrication of microneedle arrays.

[0044] As described above, each microneedle in a microneedle array may include an electrode. In some variations, multiple different types of electrodes may be included among the microneedles in the microneedle array. For example, in some variations, the microneedle array may be used as an electrochemical cell that can operate electrolytically using three types of electrodes. In other words, the microneedle array may include at least one working electrode, at least one counter electrode, and at least one reference electrode. Thus, the microneedle array may include three different electrode types, but one or more of each electrode type may form a complete system (e.g., the system may include multiple different working electrodes). Furthermore, multiple different microneedles may be electrically connected to form an effective electrode type (e.g., a single working electrode may be formed by two or more connected microneedles having working electrode sites). Each of these electrode types may include a metallization layer and may include one or more coatings or layers on the metallization layer to facilitate the function of the electrode.

[0045] Generally, the working electrode is the electrode where the oxidation and / or reduction reactions of interest occur to detect the analyte of interest. The counter electrode is used to supply (provide) or absorb (accumulate) electrons by means of current, which are required to sustain the electrochemical reaction at the working electrode. The reference electrode is used to provide a reference potential for the system; that is, the working electrode is biased at a potential relative to the reference electrode. A fixed, time-varying, or at least controlled potential relationship is established between the working electrode and the reference electrode, and within practical constraints, no current originates from or is injected into the reference electrode. Furthermore, to achieve this three-electrode system, the analyte monitoring device may include a suitable potentiostat or electrochemical simulation front end to maintain a fixed potential relationship between the working electrode and the reference electrode set within the electrochemical system (via an electronic feedback mechanism), while allowing the counter electrode to dynamically oscillate to the potential required to sustain the redox reaction of interest.

[0046] According to an implementation of the present invention, a method is provided for electrodepositing at least one surface immobilization layer on at least one working electrode contained within a wearable analyte selective sensor. The method includes: applying a capping layer comprising a redox pair to a front surface of a transducer located on a substrate surface to form a substrate-integrated reference electrode; immersing the substrate-integrated reference electrode in a fluid medium containing at least one working electrode to form an electrolytic cell; and applying electrical stimulation to the at least one working electrode. The application of electrical stimulation achieves the electrodeposition of the surface immobilization layer on at least one working electrode contained within the wearable analyte selective sensor.

[0047] Suitable processes, such as those described below, can be used to apply the individual layers of the working electrode, counter electrode, and reference electrode to the microneedle array and / or to functionalize it.

[0048] In the pretreatment step of the microneedle array, the microneedle array can be plasma-cleaned in an inert gas (e.g., an inert gas generated by RF, such as argon) plasma environment to make the surface of the material, including the electrode material, more hydrophilic and chemically reactive. This pretreatment is used not only to physically remove organic debris and contaminants, but also to clean the electrode surface and prepare it to enhance the adhesion of the subsequently deposited film on its surface.

[0049] Anodizing: To configure the working electrode after the pretreatment step, the electrode material can be anodized using an amperometric method. In this method, one or more electrode components for the function of the working electrode are subjected to a fixed high anodic potential (e.g., between +1.0V and +1.3V relative to an Ag / AgCl reference electrode) in a moderately acidic solution (e.g., 0.1M–3M H₂SO₄) for an appropriate time (e.g., between about 30 seconds and about 10 minutes). During this process, a thin and stable layer of natural oxides can be formed on the electrode surface. Any trace contaminants can also be removed due to the low pH value generated at the electrode surface.

[0050] In an alternative implementation using the coulometric method, anodizing can proceed until a specified amount of charge (in coulombs) has passed through. An anodic potential can be applied as described above; however, the duration of this process may vary until the specified amount of charge has passed through.

[0051] Activation: Following the anodizing process, cyclic voltammetry can be used during activation to subject the working electrode components to a cyclically scanned potential waveform. In activation processes that may occur in moderately strong acid solutions (e.g., H₂SO₄ between 0.1 M and 3 M), the applied potential can vary over time as a suitable function (e.g., a sawtooth function). For example, the voltage can be linearly scanned as an alternating function (e.g., a linear scan segment between 15 and 50) between cathode values ​​(e.g., between -0.3 V and -0.2 V relative to an Ag / AgCl reference electrode) and anodic values ​​(e.g., between +1.0 V and +1.3 V relative to an Ag / AgCl reference electrode). The scan rate of this waveform can be between 1 mV / sec and 1000 mV / sec. It should be noted that the current peak appearing during the anodic scan (scanning to the positive electrode) corresponds to the oxidation of the chemical substance, while the current peak appearing during the subsequent cathode scan (scanning to the negative electrode) corresponds to the reduction of the chemical substance.

[0052] Functionalization of the Biorecognition Layer: Following the activation process, the working electrode components can be functionalized using a biorecognition layer such as those described above. Assuming the working electrode assembly of the microneedle array has undergone the aforementioned steps, the applied potential can vary over time using a sawtooth function. For example, the voltage can be linearly scanned between a cathode value (e.g., approximately 0.0 V relative to an Ag / AgCl reference electrode) and an anode value (e.g., approximately +1.0 V relative to an Ag / AgCl reference electrode) using an alternating function (e.g., 10 linear scan segments). In an exemplary variant, the scan rate of this waveform can take values ​​between approximately 1 mV / sec and approximately 10 mV / sec in an aqueous solution composed of a monomeric precursor of an embedded conductive polymer and cross-linked biorecognition elements (e.g., enzymes, such as glucose oxidase). During this process, a thin film of biorecognition layer (e.g., between approximately 10 nm and approximately 1000 nm) consisting of the polymer and dispersed cross-linked biorecognition elements can be formed (e.g., by electrodeposition or electropolymerization) on the working electrode surface. In some variations, the conductive polymer may include one or more of aniline, pyrrole, acetylene, phenylene, phenylene vinylene, phenylenediamine, thiophene, 3,4-ethylidene dioxythiophene, and aminophenylboronic acid. As described above, the biometric layer imparts selective sensing capabilities for the analyte of interest.

[0053] In some variations, the working electrode surface may be electrochemically roughened to enhance the adhesion of the biorecognition layer to the electrode material surface (and / or the Pt black layer). The roughening process may involve cathodic treatment (e.g., cathodic deposition, a subset of amperometric methods), wherein the electrode is subjected to a fixed cathode potential (e.g., between -0.4 V and +0.2 V relative to an Ag / AgCl reference electrode) for a certain period of time (e.g., between 5 sec and 10 min) in an acidic solution containing the desired metal cation dissolved therein (e.g., H₂PtCl₆ between 0.01 mM and 100 mM). Alternatively, the electrode is subjected to a fixed cathode potential (e.g., between -0.4 V and +0.2 V relative to an Ag / AgCl reference electrode) in an acidic solution containing the desired metal cation dissolved therein (e.g., H₂PtCl₆ between 0.01 mM and 100 mM) until a certain amount of charge (e.g., between 0.1 mC and 100 mC) has been passed through. During this process, a thin, highly porous metal layer can be formed on the electrode surface, thereby significantly increasing the electrode surface area. Alternatively, in some variations as described above, elemental platinum metal can be deposited on the electrode to form or deposit a platinum black layer 1613.

[0054] Functionalization of the diffusion confinement layer: After functionalizing the biometric layer, in some variations, a diffusion confinement layer can be used to functionalize the working electrode components. Assuming the working electrode assembly of the microneedle array has undergone the above steps, one or more of the following methods can be used to apply the diffusion confinement layer, which can be a thin film with a thickness between about 100 nm and about 10,000 nm.

[0055] In some variations, a diffusion-limiting layer can be applied by a spraying method, in which an atomized polymer formulation (dispersed in water or a solvent) is applied to the microneedle array device in a controlled environmental setting with a specified spray pattern and duration. This forms a thin film with the desired thickness and porosity required to limit the diffusion of the analyte of interest into the biorecognition layer.

[0056] In some variations, a diffusion-confining layer can be applied via plasma-induced polymerization, in which a plasma source generates a gas discharge that provides energy to activate crosslinking reactions within a gaseous, atomized, or liquid monomer precursor (e.g., vinylpyridine). This transforms the monomer precursor into a polymer coating that can be deposited to a specified thickness on a microneedle array, thereby forming a thin film with the desired thickness and porosity required to confine the diffusion of the analyte of interest to the biorecognition layer.

[0057] In addition, in some variations, a diffusion confinement layer can be applied by electrophoretic or dielectrophoretic deposition.

[0058] Anodizing: In some variations, the electrode material may be anodized using an amperometric method, in which one or more electrode components for the electrode function are subjected to a fixed high anodic potential or an appropriate amount of time in a moderately acidic solution. Exemplary parameters and other details for the anodizing process of the electrode may be similar to those described above for the working electrode. Similarly, the anodizing of the electrode may alternatively use the coulometric method as described above.

[0059] Activation: In some variations, after the anodizing process, cyclic voltammetry can be used during activation to subject the counter electrode components to cyclically scanned potential waveforms. In some variations, the activation process can be similar to the process described above for the working electrode.

[0060] Roughening: In addition, in some variations, the electrode surface may be electrochemically roughened to enhance the current absorption or current supply capability of this electrode assembly. The electrochemical roughening process may be similar to the process described above for the working electrode. Alternatively, in some variations as described above, elemental platinum metal may be deposited on the electrode to form or deposit a platinum black layer.

[0061] Anodizing: Similar to the working electrode and counter electrode described above, the reference electrode may be anodized using an amperometric method, in which one or more electrode components for the counter electrode function are subjected to a fixed high anodic potential or an appropriate amount of time in a moderately acidic solution. Exemplary parameters and other details for the anodizing process of the counter electrode may be similar to those described above for the working electrode. Similarly, the anodizing of the counter electrode may...

[0062] Activation: Following the anodizing process, cyclic voltammetry can be used during activation to subject the reference electrode components to cyclically scanned potential waveforms. In some variations, the activation process can be similar to the process described above for the working electrode.

[0063] Functionalization: Following the activation process, the reference electrode components can be functionalized. Assuming the reference electrode assembly of the microneedle array has undergone the aforementioned steps, a fixed anodic potential (e.g., between +0.4V and +1.0V relative to an Ag / AgCl reference electrode) can be applied in an aqueous solution for a suitable duration (e.g., between about 10 seconds and about 10 minutes). Alternatively, the electrode is subjected to a fixed cathodic potential (e.g., between +0.4V and +1.0V relative to an Ag / AgCl reference electrode) in an aqueous solution until a certain amount of charge (e.g., between 0.01mC and 10mC) has passed through it. In some variations, the aqueous solution may include a monomeric precursor of a conductive polymer and a charged dopant counterion or material carrying the opposite charge (e.g., poly(styrene sulfonate)). During this process, a thin film of conductive polymer with dispersed counterions or materials (e.g., between about 10 nm and about 10,000 nm) can be formed on the surface of the reference electrode. This forms a surface-immobilized solid redox pair with a stable thermodynamic potential. In some variations, the conductive polymer may include one or more of aniline, pyrrole, acetylene, phenylene, phenylene vinylene, phenylenediamine, thiophene, 3,4-ethylenedioxythiophene, and aminophenylboronic acid.

[0064] In some alternative embodiments, a naturally occurring iridium oxide film (e.g., IrO2, Ir2O3, or IrO4) can be electrochemically grown on the surface of the iridium electrode during oxidation. As discussed above, this also forms a stable redox pair.

[0065] Furthermore, in some variations, the reference electrode surface can be electrochemically roughened to enhance the adhesion of the surface-immobilized redox pairs. The electrochemical roughening process can be similar to the process described above for the working electrode. Alternatively or additionally, in some variations as described above, elemental platinum metal can be deposited on the electrode to form or deposit a platinum black layer.

[0066] Multiple microneedles (e.g., any of the microneedle variants described herein, each of which may have a working electrode, counter electrode, or reference electrode as described above) may be arranged in a microneedle array. Considerations for configuring the microneedles include factors such as the desired insertion force for inserting the microneedle array into the skin, optimization of electrode signal levels and other performance aspects, manufacturing costs, and complexity.

[0067] For example, a microneedle array may include multiple microneedles spaced apart at a predefined interval (the distance between the center of a microneedle and the center of its nearest neighboring microneedle). In some variations, the microneedles may be spaced sufficiently to distribute the force applied to the user's skin (e.g., to avoid the "bed of nails" effect), allowing the microneedle array to penetrate the skin. As the interval increases, the force required to insert the microneedle array tends to decrease and the insertion depth tends to increase. However, it has been found that the interval only begins to affect the insertion force at low values ​​(e.g., less than about 150 μm). Therefore, in some variations, the microneedles in the microneedle array may have a interval of at least 200 μm, at least 300 μm, at least 400 μm, at least 500 μm, at least 600 μm, at least 700 μm, or at least 750 μm. For example, the interval may be between about 200 μm and about 800 μm, between about 300 μm and about 700 μm, or between about 400 μm and about 600 μm. In some variations, the microneedles can be arranged in a periodic grid, and the spacing can be uniform in all directions of the microneedle array and across all regions. Alternatively, the spacing measured along different axes (e.g., the X and Y directions) can be different and / or some regions of the microneedle array may include smaller spacing while other regions may include larger spacing.

[0068] Furthermore, for more consistent insertion, the microneedles can be spaced equidistantly (e.g., with the same spacing in all directions). For this purpose, in some variations, the microneedles in the microneedle array can be arranged in a hexagonal configuration. Alternatively, the microneedles in the microneedle array can be arranged in a rectangular array (e.g., a square array) or another suitable symmetrical arrangement.

[0069] Another consideration in determining the microneedle array configuration is the overall signal level provided by the microneedles. Generally, the signal level at each microneedle does not change with the total number of microneedle elements in the array. However, the signal level can be enhanced by electrically interconnecting multiple microneedles in the array. For example, an array with a large number of electrically connected microneedles is expected to produce greater signal strength (and thus increased accuracy) compared to an array with fewer microneedles. However, a larger number of microneedles on the diaphragm will increase the diaphragm cost (given a constant spacing) and will also require greater force and / or speed for insertion into the skin. In contrast, a smaller number of microneedles on the diaphragm can reduce diaphragm cost and allow insertion into the skin with reduced applied force and / or speed. Furthermore, in some variations, a smaller number of microneedles on the diaphragm can reduce the total area occupied by the diaphragm, which can result in less undesirable localized edema and / or erythema. Therefore, in some variations, a balance between these factors can be achieved by using a microneedle array comprising 37 microneedles or a microneedle array comprising 7 microneedles. However, in other variations, there may be fewer microneedles in the array (e.g., between about 5 and about 35, between about 5 and about 30, between about 5 and about 25, between about 5 and about 20, between about 5 and about 15, between about 5 and about 100, between about 10 and about 30, between about 15 and about 25, etc.), or there may be more microneedles in the array (e.g., more than 37, more than 40, more than 45, etc.).

[0070] Additionally, in some variations, only a subset of the microneedles in the microneedle array may be active during operation of the analyte monitoring device. For example, a portion of the microneedles in the microneedle array may be inactive (e.g., no signal is read from the electrodes of the inactive microneedles). In some variations, a portion of the microneedles in the microneedle array may be activated at specific times during operation and remain active for the remainder of the device's operating life. Furthermore, in some variations, a portion of the microneedles in the microneedle array may be additionally or alternatively deactivated at specific times during operation and remain inactive for the remainder of the device's operating life.

[0071] When considering the characteristics of microneedle array dies, the die size is a function of the number of microneedles in the microneedle array and the spacing between the microneedles. Manufacturing cost is also a consideration, as a smaller die size will help reduce costs because the number of dies that can be formed from a single wafer of a given area will increase. Furthermore, due to the relative brittleness of the substrate, a smaller die size will also reduce the likelihood of brittle fracture.

[0072] Furthermore, in some variations, it has been found that microneedles located at the periphery of the microneedle array (e.g., near the edge or boundary of the die, near the edge or boundary of the housing, near the edge or boundary of the adhesive layer on the housing, along the outer edge of the microneedle array, etc.) exhibit better performance (e.g., sensitivity) compared to microneedles at the center of the microneedle array or the bare die. Therefore, in some variations, the working electrode can be arranged mostly or completely on the microneedles located at the periphery of the microneedle array to obtain more accurate and / or precise analyte measurements.

[0073] Figure 2 and Figure 5 An exemplary schematic diagram depicts 37 microneedles arranged in an exemplary variant of a microneedle array. The 37 microneedles may, for example, be arranged in a hexagonal array, wherein the center-to-center distance between the center of each microneedle and the center of its immediate neighbor in any direction is approximately 750 μm (or between approximately 700 μm and approximately 800 μm, or between approximately 725 μm and approximately 775 μm).

[0074] Figure 1 and Figure 4 This is a perspective view depicting an exemplary schematic of seven microneedles arranged in an exemplary variant of a microneedle array. The seven microneedles are arranged in a hexagonal array on a substrate. Electrodes are arranged on the distal portions of the microneedles extending from a first surface of the substrate. The proximal portions of the microneedles are electrically connected to corresponding back-side electrical contacts on a second surface of the substrate opposite the first surface. The seven microneedles may be arranged in a hexagonal array where the center-to-center spacing between the center of each microneedle and the center of its immediate neighbor in any direction is approximately 750 μm. In other variants, the center-to-center spacing may be, for example, between approximately 700 μm and approximately 800 μm, or between approximately 725 μm and approximately 775 μm. Microneedles may have an approximate outer axis diameter of about 170 μm (or between about 150 μm and about 190 μm, or between about 125 μm and about 200 μm) and a height of about 500 μm (or between about 475 μm and about 525 μm, or between about 450 μm and about 550 μm).

[0075] Furthermore, the microneedle array described herein can have a high degree of configurability regarding the positions of one or more working electrodes, one or more counter electrodes, and one or more reference electrodes within the microneedle array. Electronic systems can facilitate this configurability.

[0076] The following description is an exemplary implementation of the current topic.

[0077] This invention aims to circumvent the limitations of liquid-junction reference electrodes by implementing a liquid-phase architecture in a solid-state embodiment, thereby enabling the synthesis of highly parallel electrochemical sensors. The solid-state embodiment is directly integrated onto a substrate and can form an electrolytic cell when immersed in a fluid containing at least one working electrode. This invention represents an alternative approach to facilitating the synthesis of substrate-integrated solid-state reference electrodes, addressing the shortcomings of prior art while remaining applicable to highly scalable manufacturing processes. These shortcomings include:

[0078] (1) Necessity of an internal filling solution that maintains thermodynamic redox equilibrium with the metal / metal salt electrode immersed therein, thereby generating a stable potential: (a) Limitations: The internal filling solution needs to be encapsulated in a relatively fragile glass capillary and requires frequent maintenance to comply with its operating specifications. This is not suitable for implementations using conventional high-throughput manufacturing processes used in the semiconductor or microelectronics industry; (b) Mitigation: Establishing a stable electrode potential by utilizing a substrate-integrated solid-state reference electrode containing an embedded redox pair, which maintains thermodynamic redox equilibrium with the electrolytic cell.

[0079] (2) Frequent maintenance intervals for conventional liquid-bonded reference electrodes: (a) Limitations: Existing liquid-bonded reference electrodes require frequent maintenance intervals to comply with operating specifications. These devices are often damaged over time due to contamination or leaching of the internal filling solution, contamination or drying of the glass frit semipermeable membrane, and the reduction in reference capacity as metal salts dissolve into the internal filling solution. These problems are known to cause the electrode potential to become unstable and deviate from the desired operating range. Therefore, these reference electrodes are often replaced periodically instead of being maintained according to proper operating specifications; (b) Mitigation: Solid-state reference electrode architectures lacking glass capillaries, internal filling solutions, and glass frit semipermeable membranes do not require maintenance intervals. Since the solid-state reference electrodes will be directly integrated into the substrate contained within the analyte selectivity sensor, these devices will be configured for use during the synthesis of a single analyte selectivity sensor, rather than being reused during the processing of another analyte selectivity sensor as in the prior art.

[0080] (3) Minimum electrolytic cell volume requirement for operating conventional liquid-bonded reference electrodes: (a) Limitations: Due to their three-dimensional geometry, existing liquid-bonded reference electrodes require a minimum fluid volume to maintain operation, typically exceeding approximately 200 microliters; (b) Mitigation: Due to their flat geometry, reference electrodes with integrated substrates can operate in electrolytic cells with much smaller liquid volumes, in some cases less than 1 microliter (e.g., electrochemical test strips for fingertip glucose determination).

[0081] (4) The labor-intensive assembly of conventional reference electrodes, which are inherently multi-part, is unsuitable for manufacturing schemes deployed in the microelectronics industry: (a) Limitations: Mechanical or manual assembly is not suitable for the micrometer or nanometer scale electrode dimensions typically encountered in microfabrication systems; (b) Mitigation: Utilizing electrodeposition processes to deposit conductive polymer films on metal electrodes of virtually any geometry. Electrodeposition processes are suitable for the automated, scalable, and highly parallel fabrication of highly uniform functional reference electrodes, thereby avoiding the need for mechanical / manual assembly as typically done in the case of conventional reference electrodes.

[0082] (5) Realization of microfabricated metal salt and metal oxide electrodes: (a) Limitations: Metal salt electrodes require chemical or electrochemical treatment of elemental metal precursors and cannot be easily synthesized using microfabrication equipment as in the case of elemental metal electrodes; (b) Mitigation measures: Elemental metal or metal alloy electrodes, traces or pads are coated with a capping layer containing embedded dopant ions, which, when immersed in solution, exhibit the same redox behavior as conventional metal salt coated metal electrodes.

[0083] (6) Formation of a semi-permeable membrane connection in a half-cell: (a) Limitations: Conventional reference electrodes extensively use glass frit semi-permeable membranes, which facilitate electrical connectivity between the internal filling liquid within the reference electrode and the surrounding fluid medium into which the reference electrode is immersed. Due to the inability to process the material using mature microfabrication techniques, it is not easy to manufacture such semi-permeable membranes using automated or semiconductor manufacturing processes; (b) Mitigation: The implementation of surface-bonded redox pairs simulates the semi-permeability of conventional glass frit membranes. These redox pairs can establish ohmic connections between the underlying metal electrode and the solution into which the fabricated solid reference electrode is immersed.

[0084] (7) Infeasibility of scaling to micrometer and submicrometer sizes: (a) Limitations: Conventional reference electrodes face difficulties when attempting to scale to sizes below the centimeter scale due to their multi-part design and extensive use of materials incompatible with conventional microfabrication and semiconductor manufacturing methods; (b) Mitigation measures: Employing manufacturing / manufacturing technologies and materials compatible with existing circuit board manufacturing and semiconductor processing infrastructure to ensure that the reference electrodes can be scaled to micrometer or submicrometer sizes and integrated on a substrate together with functional circuits and microelectromechanical systems.

[0085] (8) Added complexity of control instrument bonding: (a) Limitations: Conventional reference electrodes impose additional connectivity requirements for bonding with control instruments. These connectivity requirements add complexity, necessitate external wiring / fixtures, and consume significant space. This complexity is undesirable or inefficient in high-volume manufacturing; (b) Mitigation: The compatibility of the reference electrodes with existing circuit board manufacturing / manufacturing technologies ensures that the necessary connections are achieved prior to the introduction of batch processing.

[0086] (9) Uncontrolled reference potential drift between maintenance intervals: (a) Limitations: The target reference potential of a conventional reference electrode may drift over time as a result of contamination or leaching of the internal filling solution, contamination or drying of the glass frit semipermeable membrane, or a reduction in reference capacity between periodic maintenance intervals, which can lead to changes in the electrodeposition or electrolysis process; (b) Mitigation measures: Since the reference electrode is to be used only once, the reference potential of the reference electrode is determined by the manufacturing and storage process.

[0087] The inventions disclosed herein teach apparatus and methods for electrochemical processing and / or electrodeposition of thin films on working electrodes within analyte-selective sensors using essentially entirely solid-state substrate-integrated reference electrodes. Exemplary substrates include printed circuit boards, flexible circuits, semiconductor devices, or integrated circuits, and are generally geometrically sufficiently flat. The substrate-integrated reference electrode is implemented by depositing a thin or thick film on an underlying electrical conductor, which facilitates ohmic contact with instruments configured to control the electrodeposition process. Optionally, this method can also be used for electroplating, electrocleaning, electropolishing, anodizing, and electrochemical activation processes. Methods for depositing the thin or thick film include screen printing (mesh or shadow mask templates), spraying, drop casting, dip coating, aerosol deposition, vapor deposition, sputtering, electroplating, and anodic deposition. In some embodiments, the basic principle of using a substrate-integrated reference electrode includes depositing a surface immobilization layer on at least one working electrode in an electrolytic cell. The surface immobilization layer on at least one working electrode includes at least one of a sensing layer, a biometric layer, a diffusion-limiting layer, a biocompatible layer, and an interference-suppressing layer. Surface immobilization layers are used to enhance the selective sensing capability of analyte-selective sensors, and a certain level of accuracy is required to ensure consistency between sensor batches in the manufacturing environment.

[0088] This invention relates to a reference electrode device configured to electrodeposit at least one surface immobilization layer onto at least one of the working electrodes contained within a wearable analyte selective sensor. The reference electrode device comprises, in order from front to back surface, a surface, a substrate, a transducer, and a capping layer. The capping layer contains a redox pair. The reference electrode serves as a component of an electrolytic cell and is configured to operate in the same fluid medium as the working electrode. The surface immobilization layer includes at least one of a sensing layer, a biometric layer, a diffusion-limiting layer, a biocompatible layer, and an interference-suppressing layer. The working electrode is a metal (i.e., elements platinum, palladium, rhodium, iridium, ruthenium, rhenium, gold, nickel, titanium, chromium, tungsten, tantalum), a metal alloy (i.e., platinum-iridium, gold-nickel, palladium-gold), a semiconductor (i.e., silicon, germanium, silicon-germanium, gallium arsenide, indium gallium arsenide, gallium nitride, indium gallium nitride, indium phosphide, indium gallium phosphide), or a polymer (i.e., poly(pyrrole), poly(aniline), poly(3,4-ethylenedioxythiophene)). The analyte-selective sensor is an electrochemical sensor, transdermal sensor, dermal sensor, subcutaneous sensor, or microneedle sensor. The substrate is a printed circuit board, flexible circuit, polymer, or semiconductor device. The transducer is a trace, electrode, pad, via, contact point, or electrical connector and is made of metal, metal alloy, or metal oxide. The overlay includes at least one of a metal, metal alloy, metal oxide (i.e., IrO2 or Ir2O3), metal salt (i.e., AgCl or CuSO4), metal dispersion, metal ink, metal paste, semiconductor, and conductive polymer. The redox pair is Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2 and contributes to the formation of a stable electrode potential between -1.5 volts and +1.5 volts for the standard hydrogen electrode. Optionally, the electrolytic cell includes at least one counter electrode. The fluid medium is an aqueous solution, an electrolytic solution (i.e., a buffer in water), an ionic liquid, a solvent, or a dispersion.

[0089] This invention relates to a method for electrodepositing at least one surface immobilization layer onto at least one of the working electrodes included in a wearable analyte selective sensor, the method comprising, in the order of execution, applying a capping layer comprising a redox pair onto a front surface of a transducer located on a substrate surface to form a substrate-integrated reference electrode; immersing the substrate-integrated reference electrode in a fluid medium containing the at least one working electrode to form an electrolytic cell; and applying an electrical stimulus to the at least one working electrode, wherein the application of the electrical stimulus achieves the electrodeposition of the surface immobilization layer onto at least one of the working electrodes included in the wearable analyte selective sensor. The surface immobilization layer includes at least one of a sensing layer, a biometric layer, a diffusion-limiting layer, a biocompatible layer, and an interference-suppressing layer. The working electrode is a metal (i.e., elements platinum, palladium, rhodium, iridium, ruthenium, rhenium, gold, nickel, titanium, chromium, tungsten, tantalum), a metal alloy (i.e., platinum-iridium, gold-nickel, palladium-gold), a semiconductor (i.e., silicon, germanium, silicon-germanium, gallium arsenide, indium gallium arsenide, gallium nitride, indium gallium nitride, indium phosphide, indium gallium phosphide), or a polymer (i.e., poly(pyrrole), poly(aniline), poly(3,4-ethylenedioxythiophene)). The analyte-selective sensor is an electrochemical sensor, a transdermal sensor, a dermal sensor, a subcutaneous sensor, or a microneedle sensor. The capping layer includes at least one of a metal, a metal alloy, a metal oxide (i.e., IrO2 or Ir2O3), a metal salt (i.e., AgCl or CuSO4), a metal dispersion, a metal ink, a metal paste, a semiconductor, and a conductive polymer. The redox pair is Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2 and contributes to the formation of a stable electrode potential between -1.5 volts and +1.5 volts for the standard hydrogen electrode. Optionally, the electrolytic cell includes at least one counter electrode. The fluid medium is an aqueous solution, an electrolyte solution (i.e., a buffer in water), an ionic liquid, a solvent, or a dispersion. The electrical stimulation is at least one of DC voltage, DC current, AC voltage, AC current, a specified charge, an electrical function, or an electrical waveform.

[0090] In an alternative embodiment, the present invention relates to a method for maintaining an electrochemical reaction on at least one of the working electrodes included in a wearable analyte selective sensor, the method comprising, in the order of execution, applying a capping layer comprising a redox pair to a front surface of a transducer located on a substrate surface to form a substrate-integrated reference electrode; immersing the substrate-integrated reference electrode in a solution containing the at least one working electrode; and applying an electrical stimulus to the at least one working electrode, wherein the application of the electrical stimulus achieves an electrochemical reaction on the at least one of the working electrodes included in the wearable analyte selective sensor. The surface immobilization layer includes at least one of a sensing layer, a biometric layer, a diffusion-limiting layer, a biocompatible layer, and an interference-suppressing layer. The working electrode is a metal (i.e., elements platinum, palladium, rhodium, iridium, ruthenium, rhenium, gold, nickel, titanium, chromium, tungsten, tantalum), a metal alloy (i.e., platinum-iridium, gold-nickel, palladium-gold), a semiconductor (i.e., silicon, germanium, silicon-germanium, gallium arsenide, indium gallium arsenide, gallium nitride, indium gallium nitride, indium phosphide, indium gallium phosphide), or a polymer (i.e., poly(pyrrole), poly(aniline), poly(3,4-ethylenedioxythiophene)). The analyte-selective sensor is an electrochemical sensor, a transdermal sensor, a dermal sensor, a subcutaneous sensor, or a microneedle sensor. The capping layer includes at least one of a metal, a metal alloy, a metal oxide (i.e., IrO2 or Ir2O3), a metal salt (i.e., AgCl or CuSO4), a metal dispersion, a metal ink, a metal paste, a semiconductor, and a conductive polymer. The redox pair is Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2 and helps to form a stable electrode potential between -1.5 volts and +1.5 volts for the standard hydrogen electrode.

[0091] Optionally, the electrolytic cell includes at least one counter electrode. The fluid medium is an aqueous solution, an electrolytic solution (i.e., a buffer in water), an ionic liquid, a solvent, or a dispersion. The electrical stimulation is at least one of DC voltage, DC current, AC voltage, AC current, a specified charge, an electrical function, and an electrical waveform.

[0092] The device preferably includes a substrate, a transducer, a capping layer, an electrolytic cell, and a working electrode. The substrate provides support for a substrate-integrated reference electrode. It may also assist in confining fluid within the electrolytic cell. The substrate may include a printed circuit board, flexible circuitry, polymer, or semiconductor device. The transducer serves as a medium between the circuitry (i.e., a potentiostat, a galvanostat) and the substrate-integrated reference electrode. The transducer may include traces, electrodes, pads, vias, contacts, or electrical connectors. The transducer may include metals, metal alloys, or metal oxides. The capping layer comprises a stable redox pair having known and stable electrode potentials. The capping layer includes at least one of a metal, metal alloy, metal oxide (i.e., IrO2 or Ir2O3), metal salt (i.e., AgCl), metal dispersion, metal ink, metal paste, semiconductor, and conductive polymer. The electrolytic cell is a closed volume containing a fluid, which includes at least one of water, solvent, salt, monomer, metal ions, and deposition solution. At a minimum, the cell requires at least one working electrode and at least one reference electrode. Optionally, the cell may include at least one counter electrode. A surface immobilization layer is electrodeposited on at least one electrode in a cell to impart selective analyte sensing capability. The electrode is contained within a wearable analyte-selective sensor. The surface immobilization layer includes at least one of a sensing layer, a biometric layer, a diffusion-limiting layer, a biocompatible layer, and an interference-suppressing layer. The electrode comprises a metal, a metal alloy, a semiconductor, or a polymer. The metal is an element such as platinum, palladium, rhodium, iridium, ruthenium, rhenium, gold, nickel, titanium, chromium, tungsten, or tantalum. The semiconductor is silicon, germanium, silicon-germanium, gallium arsenide, indium gallium arsenide, gallium nitride, indium gallium nitride, indium phosphide, or indium gallium phosphide. The analyte-selective sensor is an electrochemical sensor, a transdermal sensor, a dermal sensor, a subcutaneous sensor, or a microneedle sensor.

[0093] The stable electrode potential is between -1.5 volts and +1.5 volts relative to the standard hydrogen electrode.

[0094] The first step of the method is to apply a capping layer to the front surface of a transducer located on a substrate, thereby forming a reference electrode integrated with the substrate. The capping layer comprises at least one of a metal, metal alloy, metal oxide, metal salt, metal dispersion, metal ink, metal paste, semiconductor, and conductive polymer. The capping layer contains an embedded redox pair having a stable and well-known electrode potential. The transducer is a trace, electrode, pad, via, contact point, or electrical connector. The transducer comprises a metal, metal alloy, or metal oxide. The substrate is composed of a printed circuit board, flexible circuitry, polymer, or semiconductor device.

[0095] The second step of the method is to immerse the substrate-integrated reference electrode in a solution containing at least one electrode, thereby forming a pool and achieving fluid contact between at least one electrode and the substrate-integrated reference electrode. The pool comprises at least one of water, solvent, salt, ionic liquid, monomer, metal ions, and deposition solution.

[0096] The third step of the method is to apply electrical stimulation to the at least one electrode, which achieves the deposition of a surface immobilization layer on at least one electrode contained within a wearable analyte selective sensor. The electrical stimulation may include voltage or current. The electrical stimulation may include at most one of the following techniques: amperometry, chronoamperometry, coulometric voltammetry, cyclic voltammetry, linear sweep voltammetry, electrochemical voltammetry, and potentiochemical voltammetry.

[0097] The input of this invention is a substrate-integrated reference electrode, which is an electrode comprising a redox pair having a stable and well-known electrode potential on the front surface of a sufficiently flat substrate. The stable electrode potential is between -1.5 volts and +1.5 volts relative to a standard hydrogen electrode. The substrate is a printed circuit board, flexible circuit, polymer, or semiconductor device.

[0098] The output of the present invention is to deposit a surface immobilization layer on at least one of the working electrodes contained in a wearable analyte selective sensor, said surface immobilization layer being a functional layer, thin film or membrane comprising at least one of a sensing layer, a biometric layer, a diffusion restriction layer, a biocompatible layer and an interference suppression layer.

[0099] The device preferably includes a substrate, a transducer, and a working electrode. The capping layer comprises a layer deposited on the surface of the transducer. The electrolytic cell is formed by immersing a reference electrode and a working electrode in a fluid medium.

[0100] The components of a complete electrolytic cell, characterized by a substrate-integrated reference electrode for depositing a surface immobilization layer on at least one working electrode, include: the electrolytic cell positioned on a substrate, having a transducer, a working electrode, a capping layer having embedded redox pairs, and a surface immobilization layer.

[0101] Exemplary Implementation

[0102] Implementation Scheme I-1. An apparatus comprising:

[0103] substrate;

[0104] A reference electrode, the reference electrode comprising:

[0105] A transducer, the transducer being positioned on the front surface of the substrate; and

[0106] A capping layer comprising a redox pair applied to a first surface of the transducer; and

[0107] A working electrode, wherein the working electrode is positioned on the front surface of the substrate;

[0108] The reference electrode and the working electrode form an electrolytic cell in a fluid medium;

[0109] The electrodeposition of the upper surface layer of the working electrode is achieved by applying an electrical stimulus to the working electrode in the electrolytic cell.

[0110] Implementation Scheme I-2. The apparatus as described in Implementation Scheme I-1, wherein the working electrode is a sensing element in an analyte selectivity sensor.

[0111] Implementation Scheme I-3. The apparatus of Implementation Scheme I-1, wherein the surface layer comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion restriction layer, a biocompatible layer, and an interference suppression layer.

[0112] Implementation Scheme I-4. The apparatus of Implementation Scheme I-1, wherein the working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors and polymers.

[0113] Embodiment I-5. The apparatus of Embodiment I-1, wherein the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices.

[0114] Implementation Scheme I-6. The apparatus of Implementation Scheme I-1, wherein the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors.

[0115] Implementation Scheme I-7. The apparatus as described in Implementation Scheme I-1, wherein the transducer comprises at least one selected from the group consisting of metals, metal alloys and metal oxides.

[0116] Implementation Scheme I-8. The apparatus of Implementation Scheme I-1, wherein the covering layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metal inks, metal pastes, semiconductors, and conductive polymers.

[0117] Implementation Scheme I-9. The apparatus as described in Implementation Scheme I-1, wherein the redox pair includes Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2.

[0118] Implementation Scheme I-10. The apparatus as described in Implementation Scheme I-1, wherein the redox reaction promotes the formation of a stable electrode potential.

[0119] Implementation Scheme I-11. The apparatus as described in Implementation Scheme I-10, wherein the stable electrode potential is between -1.5 volts and +1.5 volts relative to the standard hydrogen electrode.

[0120] Implementation Scheme I-12. The apparatus of Implementation Scheme I-1, wherein the application of the electrical stimulation comprises one or more of the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and electrochemical potential application.

[0121] Implementation Scheme I-13. The apparatus as described in Implementation Scheme I-1, wherein the electrolytic cell includes a counter electrode.

[0122] Implementation Scheme I-14. The apparatus of Implementation Scheme I-1, wherein the fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents, or dispersions.

[0123] Implementation Scheme I-15. A method comprising:

[0124] An apparatus is provided comprising a substrate, a reference electrode and a working electrode, wherein the reference electrode and the working electrode are positioned on a front surface of the substrate and form an electrolytic cell in a fluid medium, and wherein the reference electrode comprises a transducer positioned on the front surface of the substrate and a capping layer comprising a redox pair applied to a first surface of the transducer.

[0125] Immerse the substrate in a fluid medium; and

[0126] An electrical stimulus is applied to the working electrode, thereby causing electrodeposition of the upper surface layer of the working electrode.

[0127] Implementation Scheme I-16. The method as described in Implementation Scheme I-15, wherein the working electrode is configured to serve as a sensing element in an analyte-selective sensor.

[0128] Implementation Scheme I-17. The method of Implementation Scheme I-15, wherein the surface layer comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion restriction layer, a biocompatible layer, and an interference suppression layer.

[0129] Implementation Scheme I-18. The method of Implementation Scheme I-15, wherein the working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors and polymers.

[0130] Implementation Scheme I-19. The method of implementation Scheme I-15, wherein the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices.

[0131] Implementation Scheme I-20. The method of implementation Scheme I-15, wherein the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors.

[0132] Implementation Scheme I-21. The method of implementation scheme I-15, wherein the transducer comprises at least one selected from the group consisting of metals, metal alloys and metal oxides.

[0133] Implementation Scheme I-22. The method of Implementation Scheme I-15, wherein the coating layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metal inks, metal pastes, semiconductors, and conductive polymers.

[0134] Implementation Scheme I-23. The method as described in Implementation Scheme I-15, wherein the redox pair includes Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2.

[0135] Implementation Scheme I-24. The method as described in Implementation Scheme I-15, wherein the redox reaction promotes the formation of a stable electrode potential.

[0136] Implementation Scheme I-25. The method as described in Implementation Scheme I-24, wherein the stable electrode potential is between -1.5 volts and +1.5 volts relative to the standard hydrogen electrode.

[0137] Implementation Scheme I-26. The method of Implementation Scheme I-15, wherein the application of the electrical stimulation comprises one or more selected from the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and electrochemical potential application.

[0138] Implementation Scheme I-27. The method as described in Implementation Scheme I-15, wherein the electrolytic cell includes a counter electrode.

[0139] Implementation Scheme I-28. The method of Implementation Scheme I-15, wherein the fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents and dispersions.

[0140] For purposes of explanation, the foregoing description uses specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not essential for practicing the invention. For purposes of illustration and description, the foregoing description presents specific embodiments of the invention. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed; obviously, many modifications and variations are possible in accordance with the foregoing teachings. The embodiments were chosen and described to explain the principles of the invention and its practical application, thereby enabling those skilled in the art to utilize the invention and various embodiments with various modifications suitable for the contemplated particular uses. The following claims and their equivalents are intended to define the scope of the invention.

Claims

1. An apparatus comprising: substrate; A flat reference electrode, the reference electrode comprising: A transducer, wherein the transducer is positioned on the front surface of the substrate; as well as A capping layer comprising a redox pair applied to a first surface of the transducer; as well as Multiple working electrodes, each of which is individually addressable and positioned on a corresponding microneedle extending from the front surface of the substrate; The flat reference electrode and each of the plurality of working electrodes are immersed in an electrolytic cell formed in the same fluid medium to provide electrodeposition of a surface layer on the respective working electrode by applying electrical stimulation to each of the plurality of working electrodes in the electrolytic cell.

2. The apparatus of claim 1, wherein each working electrode is a sensing element in an analyte selectivity sensor.

3. The apparatus of claim 1, wherein the surface layer comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion restriction layer, a biocompatible layer, and an interference suppression layer.

4. The apparatus of claim 1, wherein each working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors, and polymers.

5. The apparatus of claim 1, wherein the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices.

6. The apparatus of claim 1, wherein the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors.

7. The apparatus of claim 1, wherein the transducer comprises at least one selected from the group consisting of metals, metal alloys and metal oxides.

8. The apparatus of claim 1, wherein the covering layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metal inks, metal pastes, semiconductors, and conductive polymers.

9. The apparatus of claim 1, wherein the redox pair comprises Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2.

10. The apparatus of claim 1, wherein the redox reaction promotes the formation of a stable electrode potential.

11. The apparatus of claim 10, wherein the stable electrode potential is between -1.5 volts and +1.5 volts relative to the standard hydrogen electrode.

12. The apparatus of claim 1, wherein the application of the electrical stimulation comprises one or more selected from the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and electrochemical potential application.

13. The apparatus of claim 1, wherein the electrolytic cell includes a counter electrode.

14. The apparatus of claim 1, wherein the same fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents, or dispersions.

15. A method comprising: An apparatus is provided comprising a substrate, a flat reference electrode, and a working electrode positioned on a corresponding microneedle extending from the front surface of the substrate, wherein the reference electrode is positioned on the front surface of the substrate and forms an electrolytic cell with the working electrode in the same fluid medium, and wherein the reference electrode comprises a transducer positioned on the front surface of the substrate and a capping layer comprising a redox pair applied to a first surface of the transducer. Immerse the substrate in the same fluid medium; as well as An electrical stimulus is applied to the working electrode, thereby causing electrodeposition of a surface layer on the working electrode.

16. The method of claim 15, wherein the working electrode is configured to serve as a sensing element in an analyte-selective sensor.

17. The method of claim 15, wherein the surface layer comprises at least one selected from the group consisting of a sensing layer, a biometric layer, a diffusion restriction layer, a biocompatible layer, and an interference suppression layer.

18. The method of claim 15, wherein the working electrode comprises at least one selected from the group consisting of metals, metal alloys, semiconductors, and polymers.

19. The method of claim 15, wherein the substrate comprises at least one selected from the group consisting of printed circuit boards, flexible circuits, polymers, and semiconductor devices.

20. The method of claim 15, wherein the transducer comprises at least one selected from the group consisting of traces, electrodes, pads, vias, contacts, and electrical connectors.

21. The method of claim 15, wherein the transducer comprises at least one selected from the group consisting of metals, metal alloys and metal oxides.

22. The method of claim 15, wherein the coating layer comprises at least one selected from the group consisting of metals, metal alloys, metal oxides, metal salts, metal dispersions, metal inks, metal pastes, semiconductors, and conductive polymers.

23. The method of claim 15, wherein the redox pair comprises Ag / AgCl, Cu / CuSO4, or Ir2O3 / IrO2.

24. The method of claim 15, wherein the redox reaction promotes the formation of a stable electrode potential.

25. The method of claim 24, wherein the stable electrode potential is between -1.5 volts and +1.5 volts relative to a standard hydrogen electrode.

26. The method of claim 15, wherein the application of the electrical stimulation comprises one or more selected from the group consisting of amperometric, chronoamperometric, coulometric, voltammetric, cyclic voltammetric, linear scan voltammetric, electrochemical current application, and electrochemical potential application.

27. The method of claim 15, wherein the electrolytic cell includes a counter electrode.

28. The method of claim 15, wherein the same fluid medium comprises at least one selected from the group consisting of aqueous solutions, electrolytic solutions, ionic liquids, solvents, or dispersions.

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