Nanophotonic sensors for long-term in vivo intraocular pressure monitoring and methods of forming the same

Abstract

A biosensor includes a first layer of a periodic crystalline structure and a second layer of an amorphous crystalline structure. The first and second layers are formed from a biocompatible silicone resin having a Young's modulus between 0.4 and 2.0 MPa. The biosensor has a pressure-dependent NIR resonance peak shift of less than 15 nm over a field of view of 40° and an optical pressure sensitivity between 0.38 and 2.6 nm / mm Hg. The biosensor can be formed by forming a 3D crystalline structure having a periodic amorphous crystalline first layer and an amorphous crystalline second layer. The voids of the 3D crystalline structure are filled with a biocompatible silicone / polydimethylsiloxane material. The 3D crystalline structure is removed to form an inverse structure having a first volume of amorphously arranged voids and a second volume of periodically arranged voids.

Description

TECHNICAL FIELD

[0001] The subject matter disclosed herein relates to biosensors. More specifically, the subject matter disclosed herein relates to optomechanical nanophotonic sensors, e.g., for monitoring pressure, and to methods for fabricating the same. BACKGROUND

[0002] Biosensing procedures should be easy to use so that everyone can use them. However, many currently available biosensing procedures generally involve expensive and bulky optical equipment operated by trained technicians and clinicians. Glaucoma, which can be monitored using biosensing procedures, is one of the leading causes of irreversible blindness, primarily caused by elevated intraocular pressure (IOP). Current IOP monitoring techniques have major drawbacks such as being inaccurate, not monitoring in real-time or for long periods of time, and difficulty interpreting readouts. Furthermore, IOP measurements are typically taken infrequently and can be inaccurate indirect measurements.

[0003] Current photonic applications for biosensing, such as IOP monitoring, can overcome many of the major drawbacks of other current IOP monitoring techniques by providing continuous IOP measurements, high signal-to-noise ratio (SNR) readouts, long readout distances, and compact size, but can still involve trained technicians, otherwise the sensor can provide measurement errors due to misalignment. Other advantages provided by photonic biosensing applications include compact size, no battery, and more likely to provide faster results. However, photonic biosensing structures are generally highly sensitive to the angle of incidence and polarization of light, so bench alignment by a trained user to avoid detection errors can be important. SUMMARY

[0004] One example embodiment provides a pressure sensor that can include a first layer of a periodic crystalline structure and a second layer of an amorphous crystalline structure formed on the first layer. In one embodiment, the first and second layers can include a biocompatible silicone and / or polydimethylsiloxane. In another embodiment, the first and second layers form a three-dimensional hybrid photonic crystal. In yet another embodiment, the pressure sensor can include a pressure-dependent near-infrared resonance peak shift of less than 15 nm within a 40° field of view. In yet another embodiment, the pressure sensor can include an optical pressure sensitivity in a range between and including 0.38 nm / mm Hg and 2.6 nm / mm. In one embodiment, the first and second layers can be formed of a material having a Young's modulus in a range between and including 0.1 MPa and 2.0 MPa. The optical peak reflectivity of the pressure sensor can vary as a function of changes in pressure sensed by the pressure sensor. In one embodiment, the pressure sensor can be an intraocular pressure sensor. In another embodiment, the pressure sensor can be a humidity sensor having a reflectivity that varies as a function of changes in atmospheric humidity. In yet another embodiment, the pressure sensor can be a chemical sensor having a reflectivity that varies as a function of the presence of a sensed chemical.

[0005] Example embodiments provide a method of forming a pressure sensor, which can include forming a three-dimensional crystalline structure including a first periodic crystalline structure layer and a second non-crystalline structure layer; filling voids of the three-dimensional crystalline structure with a material having a Young's modulus in a range between and including 0.4 MPa and 2.0 MPa; and removing the three-dimensional crystalline structure to form an inverse structure of the material, which can include a Young's modulus in a range between and including 0.4 MPa and 2.0 MPa, the inverse structure including a first layer including non-crystalline arranged voids and a second layer including periodically arranged voids. In one embodiment, forming the three-dimensional crystalline structure includes evaporating a polystyrene colloidal solution. In another embodiment, the first layer and the second layer can include a biocompatible silicone / polydimethylsiloxane. In yet another embodiment, the first layer and the second layer can form a three-dimensional hybrid photonic crystal. In still another embodiment, the pressure sensor can include a pressure dependent near-infrared resonance peak shift of less than 15 nm within a field of view of 40°. In one embodiment, the pressure sensor has an optical pressure sensitivity in a range between and including 0.38 nm / mm Hg and 2.6 nm / mm Hg. In another embodiment, an optical peak reflectivity of the pressure sensor varies as a function of a pressure change sensed by the pressure sensor. In one embodiment, the method further includes forming the pressure sensor as an intraocular pressure sensor. In another embodiment, the method further includes forming the pressure sensor as a humidity sensor having a reflectivity that varies as a function of atmospheric humidity changes. In yet another embodiment, the method further includes forming the pressure sensor as a chemical sensor having a reflectivity that varies as a function of a presence of a sensed chemical. BRIEF DESCRIPTION OF DRAWINGS

[0006] In the following detailed description, aspects of the subject matter disclosed herein will be described with reference to the example embodiments illustrated in the drawings, wherein:

[0007] Figure 1A An enlarged image showing an example vertical periodic non-crystalline structure of polystyrene particles according to the subject matter disclosed herein is shown;

[0008] Figure 1B Another example vertical periodic non-crystalline structure having a periodic structure region and a non-crystalline structure region according to the subject matter disclosed herein is depicted;

[0009] Figure 1C Optomechanical operation of a biosensor according to the subject matter disclosed herein is conceptually depicted;

[0010] Figure 1D shows SEM images of a periodic pattern on the left and an amorphous pattern on the right with a lattice with p = 370 nm;

[0011] Figure 2A shows a plot of displacement as a function of pressure for different Young's moduli E;

[0012] Figure 2B shows a plot of simulation of optical sensitivity as a function of Young's modulus;

[0013] Figure 2C shows a plot of reflectivity as a function of wavelength for a hybrid photonic crystal nanostructured material for E = 0.5 MPa with respect to applied pressure;

[0014] Figure 2D shows a plot of reflectivity as a function of wavelength for a hybrid photonic crystal nanostructured material for E = 0.4 MPa;

[0015] Figure 2E shows a plot of peak wavelength as a function of pressure for a hybrid photonic crystal nanostructured material for E = 0.4 MPa;

[0016] Figure 2F shows a plot of Young's modulus as a function of PDMS base component / PDMS curing agent;

[0017] Figure 2G shows a plot of Young's modulus as a function of curing temperature;

[0018] Figure 3A and Figure 3B shows plots of reflectivity as a function of wavelength for an example periodic structure and for an amorphous structure formed from an example hybrid photonic crystal nanostructured material, respectively;

[0019] Figure 3C is a plot showing simulation and experimental results of optical peak shift as a function of incident angle for a periodic structure and for an example hybrid periodic and amorphous structure;

[0020] Figure 4A shows a sequence of steps for forming a hybrid photonic crystal that will have hybrid periodic and amorphous layers in accordance with the subject matter disclosed herein;

[0021] Figure 4B shows additional time-lapse images of evaporating water-polystyrene droplets in accordance with the subject matter disclosed herein;

[0022] Figure 4Cshowing the relative order of time delay of the arrangement of polystyrene particles into periodic particle patterns and amorphous particle patterns as water-polystyrene droplets evaporate in accordance with the subject matter disclosed herein;

[0023] Figure 4D showing the order of steps to form a nanophotonic IOP sensor in accordance with the subject matter disclosed herein;

[0024] Figure 4E is a depiction of the order between 407 and 408; Figure 4D

[0025] Figure 4F shows an image of a reverse pattern of a polydimethylsiloxane material in accordance with the subject matter disclosed herein. DETAILED DESCRIPTION

[0026] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be understood by those skilled in the art that the disclosed aspects can be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the subject matter disclosed herein.

[0027] ​References to "one embodiment" or "an embodiment" throughout the specification can mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrase "in one embodiment" or "in an embodiment" or "according to one embodiment" (or other phrases having similar meanings) throughout this specification (or in any attachments or drawings) are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In this regard, the terminology "exemplary" as used herein means "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Additionally, in one or more embodiments, the particular features, structures, or characteristics can be combined in any suitable manner. Moreover, according to the context of discussion herein, a singular term can include the corresponding plural form and a plural term can include the corresponding singular form. Similarly, terms used in connection with a hyphen are occasionally inter-changeable with the corresponding non-hyphenated versions (e.g., "two- dimensional" vs. "two dimensional," "pre-determined" vs. "pre determined," "pixel-specific" vs. "pixel specific," etc.), and capitalization of articles (e.g., "Counter Clock," "Row Select," "PIXOUT," etc.) can be inter-changeable with the corresponding non-capitalized versions (e.g., "counter clock," "row select," "pixout," etc.). Such occasional inter-changeability is not to be taken as mutually inconsistent but rather as a reflection of the context in which the term is used.

[0028] Furthermore, according to the context of discussion herein, a singular term can include the corresponding plural form and a plural term can include the corresponding singular form. It will also be noted that various graphics shown and discussed herein (including component diagrams) are for illustrative purposes only and are not drawn to scale. For example, some elements can be exaggerated relative to others in order to emphasize certain features. Additionally, if deemed appropriate, reference numerals can be repeated among the figures in order to illustrate similar or corresponding elements.

[0029] The terminology used herein is for the purpose of describing some example embodiments only and is not intended to be limiting of the claimed subject matter. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0030] It will be understood that when an element or layer is referred to as being "on" or "connected to" or "coupled to" another element or layer, it can be directly on, connected or coupled to the other element or layer, or intervening elements or layers can be present. In contrast, when an element is referred to as being "directly on," or "directly connected to" or "directly coupled to" another element or layer, there are no intervening elements or layers present. Like numbers refer to like elements throughout. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0031] As used herein, the terms "first," "second," and the like, are used as labels for nouns that they directly follow so that one element is a first element or a second element, and not both. In some embodiments, and unless explicitly stated otherwise, these terms are not intended to suggest any type of ordering of the nominated elements. The terms "first" and "second" are used interchangeably and are not intended to signify one element as superior to the other element. Furthermore, the use of the terms first and second in two or more figures is used for the purpose of clarity in discussion and illustration, and is not a requirement in all embodiments. The same can hold true for the terms "leading" and "trailing." As used herein, the terms "leading" and "trailing" are used as labels for nouns that they directly follow so that one element is a leading element or a trailing element, and not both. In some embodiments, and unless explicitly stated otherwise, these terms are not intended to suggest any type of ordering of the nominated elements. The terms "leading" and "trailing" are used interchangeably and are not intended to signify one element as superior to the other element. Furthermore, the use of the terms leading and trailing in two or more figures is used for the purpose of clarity in discussion and illustration, and is not a requirement in all embodiments.

[0032] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0033] The subject matter disclosed herein provides a photonic biosensor with small size that is designed to have application-based pressure-dependent optical peak resonance shift, highly angularly insensitive over a large field of view (FOV) (±20°), and provides easy and precise measurements for long-range readings and remote monitoring. If the photonic biosensor is designed accurately, a spectrometer is not needed for detection. In one embodiment, the photonic biosensor can be configured as an IOP sensor that can be interrogated with invisible near-infrared light to provide an output reading that can not show color (e.g., white) for normal IOP but can change color (e.g., red) at elevated IOP.

[0034] In one example embodiment, the subject matter disclosed herein provides a highly miniaturized (~200 pm thick, ~500 pm diameter) optomechanical nanophotonic sensor implant that can be used for long-term, continuous, and on-demand IOP monitoring. The optomechanical nanophotonic IOP sensor can be formed from a flexible 3D hybrid photonic crystal that functions as a pressure sensitive optical resonator (Δ0.1 nm / mm Hg) and provides IOP readings with an average precision of 0.56 mm Hg in the range of 0-40 mm Hg when interrogated using near-infrared light.

[0035] The sensor disclosed herein is made from a flexible medical grade silicone structured with 3D photonic nanostructures that function as a pressure sensitive resonator with 0.1 nm / mm Hg. A manufacturing process uses a colloidal self-assembly technique on a hydrophobic substrate that acts as a template for the flexible 3D photonic nanostructures of the sensor. A 3D / inkjet printer can be used as part of the colloidal self-assembly technique. The manufacturing process provides a 3D hybrid photonic crystal (HPC) that combines periodic and amorphous morphologies with almost no millimeter-scale defects. This low-index HPC results in a broad-angle resonant reflection (40°) that ensures easy remote readout.

[0036] Figure 1A An enlarged image of an example vertical periodic-amorphous structure 100 of polystyrene particles is shown in accordance with the subject matter disclosed herein. The periodic-amorphous structure 100 of polystyrene particles can be used to form a 3D crystalline photonic biosensor structure as described herein. Figure 1A The periodic-amorphous structure properties of the optomechanical biosensor described herein are intended to be conceptually conveyed. The regions or layers 101 in the structure 100 include a periodic particle structure (or pattern) as can be seen by the regular crystalline-type arrangement of the polystyrene particles. The regions or layers 102 in the structure 100 include an amorphous structure (or particle organization) with a much more random or amorphous arrangement of the polystyrene particles. The amorphous arrangement of the layers 102 can also be seen on the surface 103 of the periodic-amorphous structure 100.

[0037] Figure 1B Another example vertical periodic-amorphous structure 100’ with periodic structure layers 101’ and amorphous structure layers 102’ is depicted in accordance with the subject matter disclosed herein. Figure 1B The periodic-amorphous structure properties of the optomechanical biosensor as disclosed herein are intended to be conceptually conveyed. The vertical periodic-amorphous structure can be used to provide incident light 110, reflected light 111, and angle Figure 1B ​A biosensor highly angularly insensitive over the large FOV range depicted. In one embodiment, the large FOV (±20°) is provided by a thin to 100 μιη periodic-amorphous structure. The arrow depicted in the hybrid periodic-amorphous structure 100' indicates an example light path within the structure 100'. The amorphous structure region 102' has much more random light paths than the light paths in the periodic structure region 101'. Note that in Figure 1B the particles are again represented as forming a hybrid periodic-amorphous structure 100'. Figure 1A and Figure 1B The voids between the particles in

[0038] Figure 1C The optomechanical operation of a biosensor 150 according to the subject matter disclosed herein is conceptually depicted. The biosensor 150 includes a photonic crystal nanostructure material 151 having voids 152. On the left side of Figure 1C a pressure Pi is applied to the biosensor 150. To interrogate the biosensor 150, a broadband spectral light 153 (e.g., near infrared (NIR) light) is incident on the surface of the biosensor 150. The biosensor 150 reflects a broadband spectral light 154 to a readout device 155, which detects the spectral content of the reflected light. In one embodiment, the reflected light can appear as white light. In one embodiment, the readout device can be the user's eye, which can detect the color change of the light reflected from the biosensor 150.

[0039] On the right side of Figure 1C a pressure P2 greater than Pi is applied to the biosensor 150. The biosensor 150 responds to the increased pressure and changes shape by shrinking the voids 152 and changing the biosensor's optical peak resonance. For example, the optical peak resonance changes, so that when the NIR light 153 is incident on the biosensor, a much narrower band of wavelengths 156 of light is reflected and can be detected by the readout device 155 (which can also be the user's eye). In one embodiment, the narrower band of wavelengths of light 156 can appear as red light. Although the pressures Pi and P2 are depicted as being applied to the top surface of the biosensor 150, it should be understood that the pressures can be applied to either side and / or both sides of the biosensor 150.

[0040] Figure 1DSEM images of a periodic pattern (left) and an amorphous pattern (right) with a lattice of p = 370 nm are shown. The optical resonance at perpendicular incidence originates from the constructive interference of parallel crystal planes with the lattice p following Bragg's law: λ = 2pn*, where λ is the resonant wavelength reflected from the nanophotonic cavity, and n* is the average refractive index of the cavity. The lattice and resonant wavelength depend on the diameter of the initial colloidal particles, which in one embodiment can be chosen as 460 nm to produce a reflection peak in NIR (800-1000 nm). The hybrid design disclosed herein provides a wide-angle optical resonance near 870 nm and a 2 nm peak shift at a 10° incident angle and a 12 nm shift at a 25° incident angle, as shown. Figures 3A-3C As shown. In contrast, the 3D periodic photonic crystal produced a resonant displacement of 38 nm, more than three times greater, at an incident angle of 25°. Finite-difference time-domain (FDTD) simulations of a periodic and hybrid sensor support the experimental peak resonant displacement as a function of the incident angle, with results obtained in Figure 3C As shown. Furthermore, due to the numerical aperture of the light-gathering system, the intensity of the periodic sensor can significantly decrease when the incident angle reaches 20°, while the signal from the hybrid sensor remains detectable up to 40° due to wide-angle scattering from the amorphous pattern. The field of view (FOV) depends on the thickness ratio of the periodic layer to the amorphous layer in the HPC. A higher proportion of amorphous layers can result in an FOV greater than 40°. However, as the proportion of amorphous layers increases, the reflected light signal (intensity) decreases. Therefore, there is a trade-off between FOV and SNR depending on the thickness ratio of the amorphous layer to the periodic layer in the HPC.

[0041] The sensitivity of a sensor's photomechanical response for a given application can be set based on the following example applications of sensors with a physiological range of 0-40 mm Hg. Sensitivity depends on the softness or Young's modulus E of the nanostructured material constituting the sensor. To determine the appropriate Young's modulus E for a specific sensor application, the displacement or deformation of the sensor under different pressures can be simulated, for example, using the finite element method.

[0042] Figure 2A The graph shows the displacement (nm) as a function of pressure (mmHg) for different Young's modulus E (MPa). Figure 2B A simulated graph of the sensitivity (nm / mmHg) as a function of Young's modulus (MPa) is shown. (See also: Regarding...) Figure 2B The defined sensitivity is

[0043]

[0044] Figure 2C The graph shows the reflectance (%) as a function of wavelength (nm) for a hybrid photonic crystal (HPC) nanostructure material with E = 0.5 MPa.Figure 2C The different curves in the figure show the displacement of the optical resonance for different pressures.

[0045] Figure 2D The graph shows the reflectance (%) as a function of wavelength (nm) for HPC nanostructure materials with E = 0.4 MPa. Figure 2D The different curves in the figure show the displacement of the optical resonance for different pressures. Figure 2E The graph shows the peak wavelength (nm) as a function of pressure (mmHg) for HPC nanostructures with E = 0.4 MPa. Figure 2E Curve 201 in the diagram represents the simulation result, and curve 202 represents the experimentally determined result. Any soft material with an E value less than 1 MPa can be used for photonic biosensor applications providing physiological pressure ranges.

[0046] Young's modulus E can be further controlled based on the mixing ratio of the base component and the curing agent, as well as the curing temperature. Figure 2F A graph showing the Young's modulus (MPa) as a function of the PDMS base component / PDMS curing agent is displayed. Figure 2G A graph showing Young's modulus (MPa) as a function of curing temperature (°C) is displayed. Figure 2F In the diagram, curve 203 represents the average result for different sample mixing ratios. Figure 2G In the figure, curve 204 represents the results for a single example mixing ratio of 21:1 for the PDMS base component and the PDMS curing agent.

[0047] Figure 3A and Figure 3B The graphs show the reflectance (%) as a function of wavelength (nm) for the periodic structure and for the amorphous structure formed from the example HPC nanostructure material, respectively.

[0048] Figure 3C This is a graph showing the simulation and experimental results of the optical peak shift (nm) as a function of the incident angle (°) for the example periodic structure and the example mixed periodic and amorphous structure. Curve 301 represents the simulation results for the periodic structure, curve 302 represents the experimental results for the periodic structure, curve 303 represents the simulation results for the mixed periodic and amorphous structure, and curve 304 represents the experimental results for the mixed periodic and amorphous structure. From Figure 3CIt can be seen that the example hybrid periodic and amorphous structure has a nearly negligible shift in optical peak for ±10° incidence angle and a shift of less than about 15 nm for ±20° incidence angle (to provide a very useful 40° FOV). In contrast, the example periodic structure has a shift in optical peak of about 10 nm for ±10° incidence angle and a shift of more than about 35 nm for ±20° incidence angle.

[0049] The arrangement of low refractive index dielectric materials (e.g., silicone material, HPC) of the optomechanical nanophotonic sensors disclosed herein reflect a band of spectrum from incident light. The reflection peak of the HPC can be described by Bragg's law: λ = 2n*p, where λ is the peak wavelength of reflected light, n* is the effective refractive index of the HPC, and p is the spacing between planes in the lattice. When light propagates through the HPC with a periodically varying dielectric constant, incident light with a specific wavelength that matches this condition will be reflected.

[0050] From the Eq. for Bragg's law, the peak reflection wavelength depends on the spacing between planes in the lattice (p) as well as the effective refractive index of the structure (n*). For optomechanical applications, p influences the reflection peak, while for gas and humidity sensing, the reflection peak varies with n*.

[0051] The average refractive index of the HPC takes the average of the refractive indices of all its components, which can be approximated by the following calculation: n* = Σn 2 V i 2 V i where n i and V i are the refractive index and volume fraction of individual components (i) that make up the photonic material, respectively. Thus, when the air within the void space of the HPC is replaced by a vapor / gas compound with a higher refractive index, the effective refractive index (n*) increases, which will cause the Bragg peak to shift towards longer wavelengths.

[0052] Figure 4A An order of steps to form a hybrid photonic crystal to have a hybrid periodicity and amorphous layer in accordance with the subject matter disclosed herein is shown. At 401, a substrate 411, such as silicon / dioxide (Si / Si02), is prepared. At 402, a hydrophobic monolayer 412 is applied to the surface of the substrate 411. In one embodiment, the hydrophobic monolayer 411 can be formed from perfluorododecyltrichlorosilane (FDTS). In one embodiment, the FDTS material can be applied to the hydrophobic monolayer 412 using a 3D / inkjet printer or any other wet processing method. The monolayer can also be other fluorinated or Teflon coatings. At 403, a water-polystyrene solution 413 is applied to the hydrophobic monolayer 412. Figure 4AThe lower left image shows a side view of an example water-polystyrene droplet on a hydrophobic monolayer. At 404, water has evaporated from the water-polystyrene solution 413, and the polystyrene has formed a mixed periodic and amorphous polystyrene particle pattern 414. The polystyrene particles can be replaced with other polymers such as PMMA or SiO2-based particles. Figure 4A The top image at the bottom right shows an example water-polystyrene droplet before evaporation, and the bottom image shows the droplet after evaporation at 50°C for approximately 45 minutes. Figure 4B Additional time-lapse images of evaporating water-polystyrene droplets are shown.

[0053] Figure 4C This illustrates the relative time lag in the arrangement of polystyrene particles into periodic and amorphous particle patterns as water-polystyrene droplets evaporate. In stage I), the polystyrene particles begin to form a periodic particle pattern 415. As evaporation progresses from stage II) to V), the periodic particle pattern 415 continues to thicken. In stage V), an amorphous particle pattern 416 begins to form. In stage VI), a mixed periodic and amorphous particle pattern 414 is formed by self-assembly into a vertical periodic-amorphous structure.

[0054] Figure 4D The sequence of steps for forming a nanophotonic IOP sensor according to the subject matter disclosed herein is shown. At 405, a cured PDMS substrate 416 with a PDMS spin coating 417 is prepared. At 406 and 407, a periodic and amorphous polystyrene particle pattern 414 is mixed (…). Figure 4A The polystyrene particle pattern 414 is transferred to the spin-coated PDMS 417. This pattern can be used as a template for fabricating the final nanophotonic sensor. At 408, the PDMS material is infiltrated into the polystyrene particle pattern, forming a PDMS-polystyrene particle pattern 414'. Optimal results are obtained when the polystyrene particle film is thicker than the spin-coated layer and capillary forces can be used to infiltrate the particle film with the spin-coated PDMS layer. At 409, the polystyrene particle pattern is removed, forming a reversed pattern of PDMS 418. The polystyrene can be removed using two possible techniques. First, it can be removed using dry etching with O2 plasma. Alternatively, it can be removed using wet etching by selectively dissolving the polystyrene particles using a remover such as PG, acetone, methyl ethyl ketone (MEK), or any developer that selectively dissolves polystyrene. Figure 4E yes Figure 4D The description of the order between 407 and 408. Figure 4F An image showing the inverted pattern of PDMS.

[0055] While the specification can include many specifics, these should not be construed as limiting the scope of any claimed subject matter, but as merely providing description of aspects of some embodiments. Some features that are described in the context of separate embodiments can also be implemented in combination with each other. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments or in any suitable sub-combination. Moreover, although features can be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be deleted from the combination, and the claimed combination can then be directed to a sub-combination or a variation of a sub-combination.

[0056] Similarly, while operations are described in a particular order in the drawings, this should not be understood as requiring the particular order of operations described or sequential order of operations, nor requiring all of the illustrated operations to be performed, to achieve desirable results. In some circumstances, multitasking and parallel processing can be advantageous. Moreover, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0057] Accordingly, particular embodiments of the subject matter have been described herein. Other embodiments are within the scope of the following claims. In some cases, actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In some implementations, multitasking and parallel processing can be advantageous.

[0058] As will be recognized by the skilled person, the innovative concepts described herein can be modified and varied widely. Accordingly, the scope of the claimed subject matter is not to be limited to any particular exemplary teachings discussed above, but is instead defined by the following claims.

[0059] This application claims priority to U.S. Provisional Application No. 63 / 068,988, filed August 21, 2020, the disclosure of which is incorporated by reference herein in its entirety.

Claims

1. A pressure sensor, comprising: a first layer of a crystalline material having particles arranged in a periodic organization to provide periodic particles; and a second layer of the crystalline material having particles arranged in an amorphous organization to provide amorphous particles, the second layer formed on the first layer, wherein the periodic particles and the amorphous particles form voids between the particles, the voids being compressible.

2. The pressure sensor of claim 1, wherein the voids are filled with a biocompatible silicone and / or polydimethylsiloxane (PDMS).

3. The pressure sensor of claim 1, wherein the first layer and the second layer form a three-dimensional hybrid photonic crystal.

5. The pressure sensor of claim 1, wherein the pressure sensor comprises an optical pressure sensitivity in a range between and including 0.38 nm / mm Hg and 2.6 nm / mm Hg.

4. The pressure sensor of claim 1, wherein the pressure sensor comprises a pressure sensing diaphragm having a thickness of less than 40 o a pressure-dependent near-infrared (NIR) resonance peak shift of less than 15 nm within the field of view.

6. The pressure sensor of claim 1, wherein the first layer and the second layer are formed of a material comprising a Young’s modulus in a range between and including 0.1 MPa and 2.0 MPa.

7. The pressure sensor of claim 1, wherein an optical peak reflectivity of the pressure sensor varies as a function of a pressure change sensed by the pressure sensor.

8. The pressure sensor of claim 1, wherein the pressure sensor comprises an intraocular pressure (IOP) sensor.

9. The pressure sensor of claim 1, wherein the pressure sensor is responsive to pressure and changes shape by compressing the voids.

10. The pressure sensor of claim 1, wherein the pressure sensor has a field of view dependent on a thickness ratio of the first layer and the second layer.

11. A method for forming a pressure sensor, the method comprising: forming a three-dimensional (3D) crystal structure comprising a first layer of a crystalline material having particles arranged in a periodic organization to provide periodic particles and a second layer of the crystalline material having particles arranged in an amorphous organization to provide amorphous particles; filling voids formed by the periodic particles and the amorphous particles with a material comprising a Young’s modulus in a range between and including 0.4 MPa and 2.0 MPa; and removing the three-dimensional (3D) crystal structure to form an inverse structure of the material comprising a Young’s modulus in a range between and including 0.4 MPa and 2.0 MPa, the inverse structure comprising a third layer comprising amorphous arranged voids and a fourth layer comprising periodically arranged voids.

12. The method of claim 11, wherein forming the three-dimensional (3D) crystal structure comprises evaporating a polystyrene colloidal solution.

13. The method of claim 11, wherein the material filled in the voids comprises a biocompatible silicone / polydimethylsiloxane (PDMS). ​ ​ 14. The method of claim 11, wherein the first layer and the second layer form a three- dimensional hybrid photonic crystal.

15. The method of claim 11, wherein the pressure sensor comprises a pressure- dependent near-infrared (NIR) resonance peak shift of less than 15 nm within a field of view of 40 o .

16. The method of claim 11, wherein the pressure sensor comprises an optical pressure sensitivity in a range between and including 0.38 nm / mm Hg and 2.6 nm / mm Hg.

17. The method of claim 11, wherein an optical peak reflectivity of the pressure sensor varies as a function of a change in pressure sensed by the pressure sensor.

18. The method of claim 11, further comprising forming the pressure sensor as an intraocular pressure (IOP) sensor.

19. The method of claim 11, wherein the pressure sensor is responsive to pressure and changes shape by compressing the void.

20. The method of claim 11, wherein the pressure sensor has a field of view that depends on a thickness ratio of the first layer and the second layer.

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