Chip-integrated nanolaminate nano-optoelectrode arrays for nonlinear optical voltage sensing

Abstract

Embodiments of a novel nanolaminate nano-optoelectrode device and method for fabricating the same are described. In one example, a nano-optoelectrode device includes a conductive substrate and a nano-optoelectrode coupled to the conductive substrate. The nano-optoelectrode includes a metal-insulator-metal nanostructure coupled to the conductive substrate. The nano-optoelectrode further includes a conductive layer coupled to the conductive substrate and to a portion of the metal-insulator-metal nanostructure. The nano-optoelectrode further includes a nanocavity plasmonic hotspot formed on an exposed portion of the metal-insulator-metal nanostructure.

Description

Attorney Docket: 222204-2870 CHIP-INTEGRATED NANOLAMINATE NANO-OPTOELECTRODE ARRAYS FOR NONLINEAR OPTICAL VOLTAGE SENSING STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with government support under grant number FA9550- 18-1-0328, awarded by the Air Force Office of Scientific Research (AFOSR). The government has certain rights in the invention. CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to U.S. Provisional Application Serial No.63 / 460,556, filed April 19, 2023, titled “CHIP-INTEGRATED NANOLAMINATE NANO-OPTOELECTRODE ARRAYS FOR NONLINEAR OPTICAL VOLTAGE SENSING” the entire contents of which are hereby incorporated herein by reference. BACKGROUND

[0003] Metallic nanostructures supporting surface plasmon modes can concentrate optical fields and enhance luminescence processes from the metal surface at plasmonic hotspots. Such nanoplasmonic metal luminescence contributes to the spectral background in surface-enhanced Raman spectroscopy (SERS) measurements and is helpful in bioimaging, nano-thermometry, and chemical reaction monitoring applications. Interest in nanoplasmonic metal luminescence is currently increasing, and some studies are investigating its dependence on voltage modulation effects. For example, some studies investigate techniques that typically ignore such voltage modulation effects such as the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) technique, which ignores voltage-dependent spectral background information associated with nanoplasmonic metal luminescence due to limited mechanistic understanding and poor measurement reproducibility. Other studies are investigating nanoplasmonic metal luminescence and its dependence on voltage modulation effects in physiological ionic solutions such as those of various neuroscience, cardiology, and cellular biology systems.Attorney Docket: 222204-2870 SUMMARY

[0004] The present disclosure is directed to a nanolaminate optoelectrode nano-array device, as well as a modular design approach and scalable fabrication process for producing such a device. The embodiments integrate out-of-plane multilayer metal-insulator-metal (MIM) nanoantennas with a conductive substrate using an angled-vapor deposition technique. Use of such an angled-vapor deposition technique allows for plasmonic hotspots of the out-of- plane multilayer MIM nanoantennas to be electrically connected to the electrode while remaining open to an external electrolyte. The embodiments provide a significant improvement over existing technologies and can be considered a voltage-sensitive nano-optical transducer in some cases with broad potential applications in fields such as biomolecule probes, electrophysiological optic-sensors, and opto-electro catalysis, among possibly others.

[0005] Aspects and advantages of embodiments of the present disclosure will be set forth in part in the following description or can be learned from the description or through practice of the embodiments. Other aspects and advantages of embodiments of the present disclosure will become better understood with reference to the appended claims and the accompanying drawings, all of which are incorporated in and constitute a part of this specification. The drawings illustrate example embodiments of the present disclosure and, together with the description, serve to explain the related concepts of the present disclosure.

[0006] According to one example embodiment, a nano-optoelectrode device includes a conductive substrate and a nano-optoelectrode coupled to the conductive substrate. The nano- optoelectrode includes a metal-insulator-metal nanostructure coupled to the conductive substrate. The nano-optoelectrode further includes a conductive layer coupled to the conductive substrate and to a portion of the metal-insulator-metal nanostructure. The nano-optoelectrode further includes a nanocavity plasmonic hotspot formed on an exposed portion of the metal- insulator-metal nanostructure. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Many aspects of the present disclosure can be better understood with reference to the following figures. The components in the figures are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the concepts of the disclosure. Moreover, repeated use of reference characters or numerals in the figures is intended to represent the same or analogous features, elements, or operations across different figures. Repeated description of such repeated reference characters or numerals is omitted for brevity.Attorney Docket: 222204-2870

[0008] FIG. 1A illustrates a cross-sectional side-view of an example nanolaminate nano- optoelectrode (NLNOE) array device according to various aspects and embodiments of the present disclosure.

[0009] FIG.1B illustrates a top-view of an example NLNOE formed on the NLNOE array device of FIG.1A according to various aspects and embodiments of the present disclosure.

[0010] FIG.1C illustrates a cross-sectional side view of the NLNOE of FIG.1B according to various aspects and embodiments of the present disclosure.

[0011] FIGS. 2A and 2B collectively illustrate a flow diagram of an example fabrication method according to various aspects and embodiments of the present disclosure. DETAILED DESCRIPTION

[0012] Metallic nanostructures can support surface plasmon modes and concentrate optical fields to enhance nanoscale luminescence processes ranging from spontaneous and stimulated emission, resonant and non-resonant Raman scattering, and nonlinear harmonic generation. Among various applications using plasmon-enhanced luminescence, surface- enhanced Raman spectroscopy (SERS) has received enormous attention as a compact biochemical detection technique with combined vibrational fingerprint specificity and plasmonic hotspot sensitivity. In addition to discrete plasmon-enhanced vibrational Raman scattering (PE-VRS) peaks from molecules at hotspots, a measured SERS spectrum often has a broad continuous emission background, typically subtracted and neglected in biochemical analyses. Recent studies reveal that the SERS background can originate from plasmon- enhanced metal luminescence at hotspots. Moreover, the past decade has seen an increasing interest in exploring plasmon-enhanced metal luminescence for applications ranging from bioimaging to nano-thermometry and chemical reaction monitoring. Nevertheless, the exact mechanism of plasmonic metal luminescence is still under debate and can involve several possible pathways, including interband photoluminescence, intraband photoluminescence, and electronic Raman scattering (ERS). Moreover, despite studies on the effects of continuous- wave (cw) or pulsed excitation conditions, excitation wavelengths, temperature, metal geometries, and metal types, little attention has been paid to investigating how the plasmonic metal luminescence depends on the applied voltage modulation at hotspots.

[0013] In a different but related field, the hyphenated electrochemical surface-enhanced Raman spectroscopy (EC-SERS) has emerged as a powerful nanoscale spectroelectrochemistry technique to simultaneously monitor molecular fingerprint information and electrochemicalAttorney Docket: 222204-2870 activities at the metal-electrolyte interface under voltage modulation, which has applications in interfacial spectroelectrochemistry analyses and biochemical sensing. Nevertheless, the EC- SERS data analysis typically ignores the spectral background information due to a poor mechanistic understanding of voltage effects on the EC-SERS background associated with plasmonic metal luminescence. Furthermore, most EC-SERS studies have employed nonuniform plasmonic devices based on metal nanoparticle aggregates or roughened metal electrodes with randomly distributed or mechanically unstable plasmonic hotspots, limiting EC-SERS measurement reproducibility for reliable analysis of voltage-dependent spectral background information.

[0014] Embodiments of the present disclosure can facilitate dynamic voltage-modulated nanoplasmonic metal luminescence from hotpots at an electrode-electrolyte interface using a multiresonant nanolaminate nano-optoelectrode (NLNOE) array device. Using EC-SERS measurements under 785 nanometers (nm) laser excitation in one implementation, it was demonstrated that example NLNOEs consisting of vertically stacked and electrically connected gold-silicon dioxide-gold (Au-SiO2-Au) nanocavities can produce voltage-sensitive (up to §30 % V-1) short-wavenumber (§93 centimeters-1(cm)-1) nanoplasmonic metal luminescence signals associated with plasmon-enhanced electronic Raman scattering (PE-ERS) in physiological ionic solutions.

[0015] Furthermore, described in some embodiments of the present disclosure is a phenomenological model that can capture plasmonic, electronic, and ionic characteristics at the metal-electrolyte interface to understand several observations, including: (i) negative voltage modulation slope for PE-ERS signals, (ii) an abrupt change in PE-ERS voltage modulation slope by switching electrode voltage polarity, and (iii) reduction of PE-ERS voltage modulation slope amplitude with increasing ionic strength. In various examples, the model intuitively reveals that (i) the observed voltage sensitivity of PE-ERS metal luminescence signals originates from spatial overlap between the metal electronic Debye length ^^^^^ and the 4thpower of surface plasmon field (|^ௌ^|ସ^ penetration depth^^ௌ^^ / 4^within a metal surface exposed to an electrolyte at hotspots, and (ii) voltage-sensitive metal luminescence from electrically connected hotspots in nano-optoelectrodes can serve as probe signals to monitor dynamic changes in microscopic capacitive characteristics (e.g., local electrolyte Debye length ^^^, local dielectric permittivity ^^^) at an electrode-electrolyte interface.

[0016] In many biomedical and environmental applications using SERS / EC-SERS, it is highly desirable to employ near-infrared (NIR) laser excitation and Au-based plasmonicAttorney Docket: 222204-2870 devices to (i) minimize molecular autofluorescence background, (ii) reduce cellular phototoxicity, (iii) ensure chemical stability and biocompatibility, and (iv) increase optical penetration depth in measurements. Embodiments of the present disclosure include Au-based NLNOEs with NIR multiresonant responses to conduct SERS / EC-SERS measurements under NIR laser excitation at 785 nm. Moreover, several studies suggest that PE-ERS can be the dominant pathway for low-wavenumber nanoplasmonic metal luminescence from metal- insulator-metal (MIM) nanogap cavities under NIR laser excitation because of the difficulty in achieving (i) intraband photoluminescence with the small incident photon energy and (ii) intraband photoluminescence with significant momentum mismatch in real-state electronic transitions across the dispersive sp-band. Recent work has further demonstrated that low- wavenumber (د100 cm-1) nanoplasmonic metal luminescence associated with PE-ERS signals from MIM nanogap cavities under the NIR laser excitation experience an |^|ସenhancement factor to serve as an internal standard for spatial and temporal calibration of PE-VRS signals in SERS measurements.

[0017] In neuroscience, cardiology, and cellular biology, accurate and reliable label-free detection of electrophysiological activities in tissues and cells is crucial for advancing our understanding of complex physiological processes. However, current nanoscale opto-electric transducers are limited by the density of exposed plasmonic hotspots that are simultaneously electrically connected to a circuit. The embodiments described herein provide a solution to this challenge in the form of a novel approach that combines scalable fabrication techniques with out-of-plane multilayer MIM nanoantennas and post-angled vapor deposition. The post-angled vapor deposition achieves a high density of electrically connected plasmonic hotspots within the nanoscale, greatly enhancing the performance of opto-electro signal transduction, electrode interface monitoring, and analysis based on in-situ electrochemical surface-enhanced Raman spectroscopy (EC-SERS), as well as biomolecule detection under voltage modulation.

[0018] The embodiments of the present disclosure provide a modular design and fabrication methodology that allows for the formation of novel nanolaminate nano- optoelectrodes (NLNOE) on a conductive substrate, with the NLNOEs being electrically coupled to one another. The embodiments have broad applications in electrophysiology-related fields such as neuroscience, cardiology, and cellular biology, among possibly others. For instance, by optically mapping electrogenic signals in real-time using any of the NLNOE array devices described herein, researchers can gain valuable insights into physiological processes that were previously difficult to study.Attorney Docket: 222204-2870

[0019] The embodiments integrate a high-performance nano-plasmonic substrate and electrochemical electrode, which allows for the direct sensing of biomolecules such as deoxyribonucleic acid (DNA) and proteins under bias voltage. This feature of the embodiments opens up new avenues for in-situ biosensing and the validation of genetic engineering techniques for multi-cell systems. Additionally, the optoelectrode technology can be used to monitor and analyze the electrophysiological activities of tissues and cells, facilitating the development of new treatments and drugs. Other potential applications include, for instance, in-situ biosensing to facilitate and validate genetic engineering of multi-cell systems and detecting biomolecules such as DNA and proteins under electrochemical modulation. Overall, the nanolaminate nano-optoelectrode technology of the embodiments offers a versatile and powerful tool for researchers and companies working in electrophysiology and related fields.

[0020] For context, FIGS.1A to 1C illustrate different views of an example nanolaminate nano-optoelectrode (NLNOE) array device 100 according to various aspects and embodiments of the present disclosure. FIG. 1A illustrates a cross-sectional side-view of the example NLNOE array device 100 according to various aspects and embodiments of the present disclosure. FIGS. 1B and 1C respectively illustrate a top and cross-sectional view of an example nanolaminate nano-optoelectrode (NLNOE) 130 of the NLNOE array device 100 of FIG. 1A according to various aspects and embodiments of the present disclosure. In this example, a bounding box 1B depicted in FIG. 1B includes the NLNOE 130 formed on the NLNOE array device 100. In this example, FIG. 1C illustrates a cross-sectional side-view of the NLNOE 130 included in the bounding box 1B of FIG.1B. The NLNOE array device 100 may be designed, embodied, and implemented as a voltage-sensitive nano-optical transducer in some cases with broad potential applications in fields such as biomolecule probes, electrophysiological optic-sensors, and opto-electro catalysis, among possibly others.

[0021] Referring to FIG. 1A, the NLNOE array device 100 includes a substrate 110. The substrate 110 in this example can be embodied as any structure on which integrated circuits, such as one or more NLNOEs, can be formed and that is capable of supporting such circuits. In the example shown, the substrate 110 can be embodied as and / or include at least one of a polymer material or composite, a metal material or alloy, a glass material or composite, a fiberglass material, a rigid or flexible circuit board (e.g., a rigid or flexible printed circuit board), a silicon (Si) material or wafer, or another type of material or substrate.

[0022] The NLNOE array device 100 also includes a conductive oxide layer such as, for instance, an indium-tin-oxide layer 120 (or “ITO layer 120”) formed on the substrate 110.Attorney Docket: 222204-2870 However, in other examples, another conductive oxide layer may be formed on the substrate 110 in place of or in addition to the ITO layer 120. In some examples, one or more conductive oxide layers other than indium-tin-oxide may be formed on the ITO layer 120. In one embodiment, the substrate 110 and the ITO layer 120 together form a conductive substrate. For instance, the substrate 110 and the ITO layer 120 together form an electrically and optically conductive substrate that can be electrically and optically coupled to one or more films, components, or structures of material formed on or otherwise coupled to such a conductive substrate as described in examples herein.

[0023] The NLNOE array device 100 further includes a periodic array of NLNOEs 130 formed on the ITO layer 120. Only a single NLNOE 130 is denoted in FIGS. 1A to 1C for clarity. Each of the NLNOEs 130 in the example shown includes a multilayered metal- insulator-metal (MIM) nanostructure, nanoantenna, and nanocavity formed as a stack of alternating nanoscale MIM films deposited on the ITO layer 120 as described herein and illustrated in FIGS. 1A and 1C. In the example shown, each of the NLNOEs 130 includes a nanolaminate nanoantenna (NLNA) 140. The NLNA 140 is designed and embodied as a multilayered metal-insulator-metal (MIM) nanostructure, nanoantenna, and nanocavity. The NLNA 140 is designed and embodied in this example as a gold-silicon dioxide (Au-SiO2) nanostructure, nanoantenna, and nanocavity. The NLNA 140 is formed as a stack of alternating nanoscale films of gold (Au) and silicon dioxide (SiO2) deposited on the ITO layer 120, although another material or materials may be relied upon in some cases. In one example, a nanoscale film or films of silver (Ag) may be used in place of or in addition to such nanoscale films of gold (Au). In the example shown, the NLNA 140 includes one or more gold (Au) films or layers 142a, 142b, 142c (or “Au layers 142”) and one or more silicon dioxide (SiO2) films or layers 144a, 144b (or “SiO2layers 144”) deposited between the Au layers 142 as illustrated in FIGS.1A and 1C.

[0024] The thickness of each of the Au layers 142 and the SiO2 layers 144 may be the same in some cases. In other examples, at least one of the Au layers 142 or the SiO2 layers 144 may have a thickness that is different from that of at least one other layer of the Au layers 142 or the SiO2 layers 144. In one example, each of the Au layers 142 is formed to an approximate thickness of 25 nm and each of the SiO2 layers 144 is formed to an approximate thickness of 10 nm, although another thickness may be relied upon in some cases for any of the Au layers 142 or the SiO2 layers 144.Attorney Docket: 222204-2870

[0025] As illustrated in FIGS. 1A and 1B, the NLNOEs 130 are formed on the NLNOE array device 100 according to a certain pattern. However, in some cases, the NLNOEs 130 may be formed on the NLNOE array device 100 according to a pattern that is different from that shown in FIGS. 1A and 1B. In other examples, a first subset of the NLNOEs 130 may be formed on the NLNOE array device 100 in a first defined pattern and a second subset of the NLNOEs 130 may be formed on the NLNOE array device 100 in a second defined pattern.

[0026] The NLNOE array device 100 further includes a conductive layer such as, for instance, a gold (Au) layer 150 (or “Au layer 150”) coated on one or more portions of the ITO layer 120 and one or more portions of at least one of the NLNAs 140, although another material may be used in place of or in addition to the Au of the Au layer 150 in some cases. For example, the Au layer 150 can be coated on portions of a top portion or surface of the ITO layer 120 and on a top and / or side portion or surface of each NLNA 140 as illustrated in FIGS.1A to 1C. In the example shown, the Au layer 150 is coated on portions of a top surface of the ITO layer 120, as well as on at least a portion of a top surface of each NLNA 140 (e.g., top surface of the Au layer 142c) and on at least a portion of a sidewall surface of each NLNA 140 (e.g., side surfaces of the Au layers 142 and the SiO2 layers 144). The Au layer 150 can be formed to varying thicknesses on such portions of the ITO layer 120 and the NLNAs 140 using an electron-beam (e-beam) evaporation process as described in examples herein.

[0027] In one example, an oblique-angle e-beam evaporation process can be performed to deposit the Au layer 150 on portions of the ITO layer 120 and a top and / or side surface (e.g., sidewall) of each of the NLNAs 140 as illustrated in FIGS.1A to 1C. For instance, an oblique- angle e-beam evaporation process can be performed to deposit the Au layer 150 on the ITO layer 120 and the NLNAs 140 at an oblique angle relative to at least one of the substrate 110 (e.g., relative to a bottom surface of the substrate 110) or the ITO layer 120 (e.g., relative to a top surface of the ITO layer 120). In one example, the oblique-angle e-beam evaporation process can be performed at an oblique angle of approximately 50 degrees (§50°), although another angle may be relied upon in some cases. For instance, during the oblique-angle e-beam evaporation process, the substrate 110, the ITO layer 120, and the NLNAs 140 can be tilted approximately 50°. For example, the substrate 110 can be positioned in a plane that is tilted approximately 50° relative to a plane that the substrate 110 would otherwise be positioned in during a normal-angle e-beam evaporation process. In one embodiment, the Au layer 150 can be formed to an approximate thickness of 30 nm, although another thickness may be relied upon in some cases. As shown in FIG.1B, arrays of diagonally oriented Au nanoholes havingAttorney Docket: 222204-2870 approximately elliptic or semi-circular shape are formed at the base of the NLNOEs 130 (e.g., adjacent to the hotspots 160) due to the shadowing effect during the oblique-angled e-beam evaporation deposition process.

[0028] In the example shown, depositing the Au layer 150 on portions of the ITO layer 120 and a top and / or side surface (e.g., sidewall) of each of the NLNAs 140 using the above- described oblique-angle e-beam evaporation process yields the NLNOE array device 100 having the NLNOEs 130 and metal-insulator-metal (MIM) multi-nanogap nanocavity plasmonic hotspots 160 (or “hotspots 160”). Only a single hotspot 160 is denoted in FIGS.1A to 1C for clarity. For instance, as a result of applying the Au layer 150 by way of such an oblique-angle e-beam evaporation process, the hotspots 160 are formed on the NLNOE array device 100 as illustrated in FIGS.1A to 1C. For example, each hotspot 160 is formed or defined as and thus includes an exposed side portion or surface of a NLNA 140 where the Au layer 150 was not deposited during the oblique-angle e-beam evaporation process, due to the aforementioned tilt angle of approximately 50°. In the example shown, each hotspot 160 is formed or defined as and thus includes exposed side portions (e.g., exposed side surfaces) of the Au layers 142 and the SiO2 layers 144 where the Au layer 150 was not deposited during the oblique-angle e-beam evaporation process, due to the aforementioned tilt angle of approximately 50°. The exposed side surfaces of the Au layers 142 and the SiO2 layers 144 forming each hotspot 160 are designed and fabricated such that they are not coated by the Au layer 150 and thus can be exposed to various physiological ionic solutions (e.g., electrolytes) when the NLNOE array device 100 is implemented. During implementation of the NLNOE array device 100, the NLNAs 140, the hotspots 160, and portions of the Au layer 150 formed on a top and / or side surface of the NLNAs 140 allow for nonlinear optical voltage sensing in various physiological ionic solutions (e.g., electrolytes) as described in examples herein.

[0029] Portions on the ITO layer 120 and the NLNAs 140 where the Au layer 150 is deposited by way of the aforementioned oblique-angle e-beam evaporation process may be referred to herein as “coated portions.” Exposed portions on the NLNAs 140 forming the hotspots 160 where the Au layer 150 is not deposited by way of the aforementioned oblique- angle e-beam evaporation process may be referred to herein as “uncoated portions.”

[0030] Each of the NLNOEs 130 in the example shown is formed by and thus includes an NLNA 140, a hotspot 160, and portions of the Au layer 150 deposited on and adjacent to the NLNA 140 by way of the aforementioned oblique-angle e-beam evaporation process. The NLNOEs 130 (e.g., their respective NLNAs 140 and hotspots 160) are electrically and opticallyAttorney Docket: 222204-2870 coupled to one another, the ITO layer 120, and the substrate 110 at least in part by way of the Au layer 150. For instance, the substrate 110 and the ITO layer 120 together form a conductive substrate in the example shown. In this example, the substrate 110 and the ITO layer 120 together form an electrically and optically conductive substrate that is electrically and optically coupled to the NLNA 140 and the hotspot 160 of each of the NLNOEs 130 at least in part by way of the Au layer 150 as described herein and illustrated in FIGS.1A to 1C.

[0031] The NLNOE array device 100 may be used to perform various bio-interfacing operations in different living systems. In one example, the NLNOE array device 100 may be implemented to perform one or more sensing or interactive bio-interfacing operations, including electrophysiology-related operations in various living multicellular systems. For instance, the NLNOE array device 100 may be implemented to perform at least one of bioelectrical, biochemical, biophotonic, or biomimetic operations in various living systems. The NLNOE array device 100 may be implemented to perform several of such bio-interfacing or electrophysiology-related operations sequentially in some examples, or concurrently (e.g., simultaneously) in other examples.

[0032] The design of the NLNOEs 130 such as the shape, materials used, and material arrangement, among other aspects, may vary depending on a particular bio-interfacing application or to achieve a desired result from a particular bio-interfacing operation. The NLNOE array device 100 and / or any of the components thereof, such as the NLNOEs 130, can be fabricated according to method 200 described herein with reference to FIGS. 2A and 2B. The method 200 provides a modular design approach and fabrication process for fabricating nanolaminate nano-optoelectrodes on a conductive substrate to form one or more of the nanolaminate nano-optoelectrode array devices described in examples herein.

[0033] FIGS. 2A and 2B collectively illustrate a flow diagram of an example fabrication method 200 (or “method 200”) according to various aspects and embodiments of the present disclosure. Example processing steps 210, 220, 230 of the method 200 are illustrated in FIG. 2A and described herein, and example processing steps 240, 250, 260, 270 of the method 200 are illustrated in FIG. 2B and described herein. The method 200 can be implemented to fabricate the NLNOE array device 100 described herein with reference to FIGS.1A to 1C. The example embodiment illustrated in FIGS. 2A and 2B depicts operations or processing steps performed in a particular order for purposes of illustration and discussion. Those of ordinary skill in the art, using the disclosures provided herein, will understand that various operations or processing steps of the method 200 or any of the other methods disclosed herein may beAttorney Docket: 222204-2870 adapted, modified, rearranged, performed simultaneously, include operations or processing steps not illustrated, and / or altered in various ways without deviating from the scope of the present disclosure.

[0034] Although the method 200 is described herein in connection with fabricating an array of nanolaminate nano-optoelectrodes (NLNOEs) on a conductive substrate, the method 200 is not so limited. For instance, the method 200 can be implemented to fabricate one or more NLNOEs on a conductive substrate such that each of the NLNOEs includes a nanolaminate nanoantenna (NLNA) formed on a conductive oxide layer with an electrically conductive layer formed on portions of the conductive oxide layer and on a top and / or side surface of the NLNA. For clarity, FIG.2 only depicts the processing steps 210, 220, 230, 240, 250, 260, 270 for three NLNOEs, such as, for instance, three of the NLNOEs 130. However, such processing steps of the method 200 may be implemented as described herein to fabricate a single NLNOE or a plurality of NLNOEs on a conductive substrate.

[0035] At processing step 210, the method 200 includes forming a reusable inverse perfluoropolyether (PFPE) nanopillar template that can be used to form a nanohole array pattern in a film, layer, or solution of polymethyl methacrylate (PMMA). For instance, the processing step 210 includes forming a polyurethane (PU) adhesion layer 214 (or “PU adhesion layer 214”) on a polyethylene terephthalate (PET) carrier substrate 212 (or “PET carrier substrate 212”). The processing step 210 further includes forming or positioning a structure of perfluoropolyether (PFPE) nanopillars 216 (or “PFPE nanopillars 216”) on the polyurethane (PU) adhesion layer 214 to couple the PFPE nanopillars 216 to the PET carrier substrate 212. Only a single PFPE nanopillar 216 is denoted in FIGS. 2A and 2B for clarity. The processing step 210 further includes forming a polymethyl methacrylate (PMMA) layer 218 (or “PMMA layer 218”) on the PFPE nanopillars 216 as illustrated in FIG. 2A. For instance, at the processing step 210, a diluted PMMA solution can be applied onto the PFPE nanopillars 216. As described herein, the diluted PMMA solution can then be spin-coated to form the PMMA layer 218 on the PFPE nanopillars 216.

[0036] At processing step 220, the method 200 further includes spin-coating the aforementioned diluted PMMA solution on the PFPE nanopillars 216. Following spin-coating, the PMMA layer 218 has a nanowell array formed therein by way of the PFPE nanopillars 216. In addition to spin-coating the PMMA layer 218 on the PFPE nanopillars 216, the processing step 220 of the method 200 further includes performing a thermal nanoimprinting process to transfer the PMMA layer 218 having the nanowell array onto a conductive oxide layer such as,Attorney Docket: 222204-2870 for instance, an indium-tin-oxide (ITO) layer 224 (or “ITO layer 224”) that is formed on a glass substrate 222. During the thermal nanoimprinting process the PMMA layer 218 is coupled to the ITO layer 224 as illustrated in FIG.2.A.

[0037] As should be appreciated, the processing steps 210, 220 collectively involve performing a reverse nanoimprinting technique to create large area, uniform NLNOE arrays on planar substrates. In one example, a reusable inverse template of perfluoropolyether (PFPE) nanopillar arrays on a polyethylene terephthalate (PET) carrier substrate was replicated at the processing steps 210, 220 from a silicon master of square nanowell array (e.g., diameter § 120 nm, depth § 300 nm, and periodicity § 400 nm) by nanoimprint lithography. With relatively low surface energy and relatively high young modulus, the PFPE template illustrated in FIG. 2A can allow a reverse nanoimprinting process to ultimately create a deposition mask of polymethyl methacrylate (PMMA) nanohole array patterns on planar substrates. For example, at the processing steps 210, 220 of the method 200 a diluted PMMA solution can be spin-coated on a hydrophobic PFPE nanopillar array to form a PMMA layer having a nanowell array formed therein. In this example, thermal nanoimprinting can then be performed at the processing step 220 to transfer the PMMA layer having the nanowell array onto an indium-tin- oxide (ITO) coated glass slide.

[0038] At processing step 230, the method 200 further includes releasing the PFPE template to transfer the PMMA layer 218 having the nanowell array onto the ITO layer 224 formed on the glass substrate 222. For instance, the PMMA layer 218 of the PFPE template is coupled to the ITO layer 224 during the above-described thermal nanoimprinting process performed at the processing step 220. During or following the thermal nanoimprinting process, the PFPE nanopillars 216 and the PET carrier substrate 212 are then released and separated from the PMMA layer 218 at the processing step 230. Upon such separation, an array of PMMA nanowells 232 are formed in the PMMA layer 218, which remains coupled to the ITO layer 224 as illustrated in FIG. 2A. Only a single PFPE nanowell 232 is denoted in FIG. 2A for clarity.

[0039] At processing step 240, the method 200 further includes performing a reactive ion etching (RIE) process to convert the PMMA nanowells 232 formed in the PMMA layer 218 to PMMA nanoholes 242 as illustrated in FIG.2B. Only a single PMMA nanohole 242 is denoted in FIG. 2B for clarity. Performing such an RIE process at the processing step 240 yields a deposition mask that can be used to deposit alternating layers of material on the PMMA layer 218 and in the PMMA nanoholes 242 as described herein.Attorney Docket: 222204-2870

[0040] At processing step 250, the method 200 further includes performing an electron- beam (e-beam) evaporation process to deposit alternating layers of gold (Au) films or layers 252 and silicon dioxide (SiO2) films or layers 254 on the PMMA layer 218 and in the PMMA nanoholes 242. Only a single layer of the Au layers 252 and a single layer of the SiO2layers 254 are denoted in FIG. 2B for clarity. In the example shown, a normal-angle e-beam evaporation process can be performed at the processing step 250 to deposit alternating layers of the Au layers 252 and the SiO2layers 254 on the PMMA layer 218 and in the PMMA nanoholes 242 as illustrated in FIG. 2B. For example, a normal-angle e-beam evaporation process can be performed at the processing step 250 to deposit alternating layers of the Au layers 252 and the SiO2layers 254 on a top surface of the PMMA layer 218 and a top surface of the ITO layer 224 in the PMMA nanoholes 242 as illustrated in FIG. 2B. In one example, each of the Au layers 252 is formed to an approximate thickness of 25 nm at the processing step 250 and each of the SiO2 layers 254 is formed to an approximate thickness of 10 nm, although another thickness may be relied upon in some cases for any of the Au layers 252 or the SiO2 layers 254.

[0041] At processing step 260, the method 200 further includes removing the PMMA layer 218, as well as the Au layers 252 and the SiO2 layers 254 deposited on the PMMA layer 218 to yield multilayered metal-insulator-metal (MIM) nanolaminate nanoantennas (NLNA) 262 (or “NLNAs 262”) formed on the ITO layer 224. Only a single NLNA 262 is denoted in FIG. 2B for clarity. To remove the PMMA layer 218, as well as the Au layers 252 and the SiO2layers 254 deposited thereon, the PMMA layer 218 can be dissolved in anisole to lift off all such layers and yield a discrete array of the NLNAs 262 formed as multilayered MIM nanocavities on the ITO layer 224.

[0042] Each of the NLNAs 262 in the example shown is embodied as a multilayered metal-insulator-metal (MIM) nanostructure, nanoantenna, and nanocavity formed as a stack of alternating nanoscale MIM films deposited on the ITO layer 224 as described herein and illustrated in FIG. 2B. In the example shown, each of the NLNAs 262 is embodied as a gold- silicon dioxide (Au-SiO2) nanostructure, nanoantenna, and nanocavity formed as a stack of alternating nanoscale films of the Au layers 252 and the SiO2 layers 254 deposited on the ITO layer 224, although another material or materials may be relied upon in some cases. In one example, a nanoscale film or films of silver (Ag) may be used in place of or in addition to any or all of the Au layers 252.Attorney Docket: 222204-2870

[0043] At processing step 270, the method 200 further includes performing an electron- beam (e-beam) evaporation process to deposit a conductive layer such as, for example, a gold (Au) layer 272 on one or more portions of the ITO layer 224 and one or more portions of the NLNAs 262. For instance, an oblique-angle e-beam evaporation process can be performed at the processing step 270 to deposit the Au layer 272 on portions of the ITO layer 224 and a top and / or side surface (e.g., sidewall) of each of the NLNAs 262 as illustrated in FIG. 2B. For example, an oblique-angle e-beam evaporation process can be performed at processing step 270 to deposit the Au layer 272 on the ITO layer 224 and the NLNAs 262 at an oblique angle relative to at least one of the glass substrate 222 (e.g., relative to a bottom surface of the glass substrate 222) or the ITO layer 224 (e.g., relative to a top surface of the ITO layer 224). In one example, the oblique-angle e-beam evaporation process can be performed at an oblique angle of approximately 50 degrees (§50°), although another angle may be relied upon in some cases. For instance, during the oblique-angle e-beam evaporation process, the glass substrate 222, the ITO layer 224, and the NLNAs 262 can be tilted approximately 50°. For example, the glass substrate 222 can be positioned in a plane that is tilted approximately 50° relative to a plane that the glass substrate 222 was positioned in when the normal-angle e-beam evaporation process was performed at the processing step 250. In one example, the Au layer 272 is formed to an approximate thickness of 30 nm at the processing step 270, although another thickness may be relied upon in some cases.

[0044] In the example shown, depositing the Au layer 272 on portions of the ITO layer 224 and a top and / or side surface (e.g., sidewall) of each of the NLNAs 262 using the above- described oblique-angle e-beam evaporation process yields a nanolaminate nano-optoelectrode (NLNOE) array device 274 having nanolaminate nano-optoelectrodes (NLNOE) 276 and metal-insulator-metal (MIM) multi-nanogap nanocavity plasmonic hotspots 278 (or “hotspots 278”). Only a single NLNOE 276 and a single hotspot 278 are denoted in FIG. 2B for clarity. The NLNOE array device 274 illustrated in FIG.2B is an alternative example embodiment of the NLNOE array device 100 described herein with reference to FIGS. 1A to 1C. In one embodiment, the NLNOE array device 274 can include the same or similar structure, properties, and functionality as that of the NLNOE array device 100.

[0045] As a result of applying the Au layer 272 by way of the above-described oblique- angle e-beam evaporation process, the hotspots 278 are formed on the NLNOE array device 274 as illustrated in FIG. 2B. For example, each hotspot 278 is formed or defined as and thus includes an exposed side portion or surface of a NLNA 262 where the Au layer 272 was notAttorney Docket: 222204-2870 deposited during the oblique-angle e-beam evaporation process, due to the aforementioned tilt angle of approximately 50°. In the example shown, each hotspot 278 is formed or defined as and thus includes exposed side portions (e.g., exposed side surfaces) of the Au layers 252 and the SiO2layers 254 where the Au layer 272 was not deposited during the oblique-angle e-beam evaporation process, due to the aforementioned tilt angle of approximately 50°. The exposed side surfaces of the Au layers 252 and the SiO2layers 254 forming each hotspot 278 are designed and fabricated such that they are not coated by the Au layer 272 and thus can be exposed to various physiological ionic solutions (e.g., electrolytes) when the NLNOE array device 274 is implemented. During implementation of the NLNOE array device 274, the NLNAs 262, the hotspots 278, and portions of the Au layer 272 formed on a top and / or side surface of the NLNAs 262 allow for nonlinear optical voltage sensing in various physiological ionic solutions as described in examples herein.

[0046] Each of the NLNOEs 276 in the example shown is formed by and thus includes an NLNA 262, a hotspot 278, and portions of the Au layer 272 deposited on and adjacent to the NLNA 262 by way of the aforementioned oblique-angle e-beam evaporation process. The NLNOEs 276 (e.g., their respective NLNAs 262 and hotspots 278) are electrically and optically coupled to one another, the ITO layer 224, and the glass substrate 222 at least in party by way of the Au layer 272. For instance, the glass substrate 222 and the ITO layer 224 together form a conductive substrate in the example shown. For example, the glass substrate 222 and the ITO layer 224 together form an electrically and optically conductive substrate that can be electrically and optically coupled to one or more films, components, or structures of material formed on or otherwise coupled to such a conductive substrate as described in examples herein. In the example shown, the glass substrate 222 and the ITO layer 224 together form an electrically and optically conductive substrate that is electrically and optically coupled to the NLNA 262 and the hotspot 278 of each of the NLNOEs 276 at least in part by way of the Au layer 272 as described herein and illustrated in FIG.2B.

[0047] As should be appreciated, at the processing step 270 an angled (e.g., §50 °) deposition by e-beam evaporation can be performed to form a sidewall coating of §30 nm thick Au on one side of NLNAs, connecting nanocavities to a conductive substrate ground to yield uniform NLNOE arrays. The sidewall coating from angled e-beam deposition can enable voltage modulation of hotspots in EC-SERS measurements while leaving one side of NLNOEs uncovered to expose plasmonic nanocavity hotspots to an electrolyte environment.Attorney Docket: 222204-2870

[0048] Example implementations of the NLNOE array device 100 described in embodiments herein demonstrated a substantial capacitive voltage modulation (e.g., up to §30 % V-1) of nanoplasmonic metal luminescence associated with PE-ERS signals from hotpot at an electrode-electrolyte interface using multiresonant NLNOE arrays (e.g., the NLNOEs 130). Embodiments of the NLNOE array device 100 provide a simple phenomenological model to capture critical plasmonic, electronic, and ionic characteristics at the metal-electrolyte interface (e.g., at the hotspots 160) to understand experimental observations, which can also provide guidelines for further performance improvement. Significantly, implementations of embodiments herein reveals that the voltage modulation of PE-ERS metal luminescence signals originates from the spatial overlap between the plasmonic mode |^ௌ^|ସpenetration ௗ ^ depthೄುସ and electronic Debye length ^^^for the electrolyte-exposed metal surface at hotspots (e.g., at the surfaces of the Au layers 142 and the SiO2layers 144 of the hotspots 160) and can follow the changes in microscopic capacitive characteristics (e.g., local electrolyte Debye length ^^^, local dielectric permittivity ^^^) at the electrode-electrolyte interface (e.g., at a top surface of the Au layer 150). The embodiments described herein represent a critical step toward the general application of nanoplasmonic metal luminescence in optical voltage biosensing, hybrid optical-electrical signal transduction, and interfacial monitoring of electrochemical processes.

[0049] Disjunctive language, such as the phrase “at least one of X, Y, or Z,” unless specifically stated otherwise, is to be understood with the context as used in general to present that an item, term, or the like, can be either X, Y, or Z, or any combination thereof (e.g., X, Y, and / or Z). Thus, such disjunctive language is not generally intended to, and should not, imply that certain embodiments require at least one of X, at least one of Y, or at least one of Z to be each present. As referenced herein in the context of quantity, the terms “a” or “an” are intended to mean “at least one” and are not intended to imply “one and only one.”

[0050] As referred to herein, the terms “include,” “includes,” and “including” are intended to be inclusive in a manner similar to the term “comprising.” As referenced herein, the terms “or” and “and / or” are generally intended to be inclusive, that is (i.e.), “A or B” or “A and / or B” are each intended to mean “A or B or both.” As referred to herein, the terms “first,” “second,” “third,” and so on, can be used interchangeably to distinguish one component or entity from another and are not intended to signify the location, functionality, or importance of the individual components or entities. As referenced herein, the terms “couple,” “couples,” “coupled,” and / or “coupling” refer to chemical coupling (e.g., chemical bonding),Attorney Docket: 222204-2870 communicative coupling, electrical and / or electromagnetic coupling (e.g., capacitive coupling, inductive coupling, direct and / or connected coupling), mechanical coupling, operative coupling, optical coupling, and / or physical coupling.

[0051] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations set forth for a clear understanding of the principles of the disclosure. Many variations and modifications can be made to the above- described embodiment(s) without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure and protected by the following claims.

Claims

Attorney Docket: 222204-2870 CLAIMS Therefore, at least the following is claimed:

1. A nano-optoelectrode device, comprising: a conductive substrate; and a nano-optoelectrode coupled to the conductive substrate, the nano-optoelectrode comprising: a metal-insulator-metal nanostructure coupled to the conductive substrate; a conductive layer coupled to the conductive substrate and to a portion of the metal-insulator-metal nanostructure; and a nanocavity plasmonic hotspot comprising an exposed portion of the metal- insulator-metal nanostructure.

2. The nano-optoelectrode device of claim 1, wherein the conductive substrate comprises: a glass substrate; and a conductive oxide layer coupled to the glass substrate.

3. The nano-optoelectrode device of claim 1, wherein the metal-insulator-metal nanostructure comprises a metal-insulator-metal nanoantenna and nanocavity.

4. The nano-optoelectrode device of claim 1, wherein the metal-insulator-metal nanostructure comprises a gold-silicon dioxide nanostructure, nanoantenna, and nanocavity.

5. The nano-optoelectrode device of claim 1, wherein the metal-insulator-metal nanostructure comprises alternating nanoscale layers of gold and silicon dioxide deposited on the conductive substrate.

6. The nano-optoelectrode device of claim 1, wherein the metal-insulator-metal nanostructure comprises: a first gold layer coupled to the conductive substrate; a first silicon dioxide layer coupled to the first gold layer; a second gold layer coupled to the first silicon dioxide layer;Attorney Docket: 222204-2870 a second silicon dioxide layer coupled to the second gold layer; and a third gold layer coupled to the second silicon dioxide layer and the conductive layer.

7. The nano-optoelectrode device of claim 1, wherein: the conductive substrate comprises a conductive oxide layer coupled to a glass substrate; the metal-insulator-metal nanostructure comprises alternating nanoscale layers of gold and silicon dioxide deposited on the conductive oxide layer; and the conductive layer is coupled to a top surface of the conductive oxide layer, a top surface of a gold layer of the alternating nanoscale layers of gold and silicon dioxide, and a side surface of each gold and silicon dioxide layer of the alternating nanoscale layers of gold and silicon dioxide.

8. The nano-optoelectrode device of claim 7, wherein the nanocavity plasmonic hotspot comprises exposed side surfaces of the alternating nanoscale layers of gold and silicon dioxide, each of the exposed side surfaces being different from the top surface of the gold layer of the alternating nanoscale layers of gold and silicon dioxide and different from the side surface of each gold and silicon dioxide layer of the alternating nanoscale layers of gold and silicon dioxide.

9. The nano-optoelectrode device of claim 1,wherein: the portion of the metal-insulator-metal nanostructure where the conductive layer is coupled is different from the exposed portion of the metal-insulator-metal nanostructure where the nanocavity plasmonic hotspot is located; and the metal-insulator-metal nanostructure and the nanocavity plasmonic hotspot are optically and electrically coupled to the conductive substrate at least in part by way of the conductive layer.

10. The nano-optoelectrode device of claim 1, further comprising: a plurality of second nano-optoelectrodes coupled to the conductive substrate and to the nano-optoelectrode, each of the plurality of second nano-optoelectrodes comprising: a second metal-insulator-metal nanostructure coupled to the conductive substrate;Attorney Docket: 222204-2870 a first portion of the conductive layer, the first portion being coupled to the conductive substrate; a second portion of the conductive layer, the second portion being coupled to the second metal-insulator-metal nanostructure; and a second nanocavity plasmonic hotspot comprising an exposed portion of the second metal-insulator-metal nanostructure.

11. A method of fabricating a nano-optoelectrode device, the method comprising: depositing alternating nanoscale layers of a metal material and an insulator material on a conductive substrate to form a metal-insulator-metal nanostructure on the conductive substrate; depositing a conductive layer on the conductive substrate and a portion of the metal- insulator-metal nanostructure; and forming a nanocavity plasmonic hotspot on an exposed portion of the metal-insulator- metal nanostructure based on depositing the conductive layer on the conductive substrate and the portion of the metal-insulator-metal nanostructure.

12. The method of claim 11, wherein depositing the alternating nanoscale layers of the metal material and the insulator material on the conductive substrate comprises: depositing an indium-tin-oxide layer on a glass substrate to form the conductive substrate; and performing a normal-angle electron-beam evaporation process using a deposition mask having a nanohole array pattern to deposit the alternating nanoscale layers of the metal material and the insulator material on a top surface of the indium-tin-oxide layer in a nanohole of the nanohole array pattern.

13. The method of claim 11, wherein depositing the conductive layer comprises: performing an oblique-angle electron-beam evaporation process to deposit the conductive layer on the conductive substrate and the portion of the metal-insulator-metal nanostructure at an oblique angle relative to the conductive substrate.

14. The method of claim 11, wherein depositing the conductive layer comprises:Attorney Docket: 222204-2870 performing an oblique-angle electron-beam evaporation process to deposit the conductive layer on the conductive substrate and the portion of the metal-insulator-metal nanostructure at an oblique angle of approximately 50 degrees relative to the conductive substrate.

15. The method of claim 14, further comprising: coupling, optically and electrically, the metal-insulator-metal nanostructure and the nanocavity plasmonic hotspot to the conductive substrate based in part on depositing the conductive layer on the conductive substrate and the portion of the metal-insulator-metal nanostructure at the oblique angle of approximately 50 degrees relative to the conductive substrate.

16. A nano-optoelectrode device, comprising: a conductive substrate; a nanostructure coupled to the conductive substrate, the nanostructure comprising alternating nanoscale layers of a metal material and an insulator material; a conductive layer coupled to the conductive substrate and to a portion of each layer of the alternating nanoscale layers of the metal material and the insulator material; and a nanocavity plasmonic hotspot comprising exposed portions of the alternating nanoscale layers of the metal material and the insulator material.

17. The nano-optoelectrode device of claim 16, wherein: the conductive substrate comprises a conductive oxide layer coupled to a glass substrate; and the nanostructure comprises alternating nanoscale layers of gold and silicon dioxide formed on the conductive oxide layer as a gold-silicon dioxide nanostructure, nanoantenna, and nanocavity.

18. The nano-optoelectrode device of claim 16, wherein: the conductive substrate comprises a conductive oxide layer coupled to a glass substrate; the nanostructure comprises alternating nanoscale layers of gold and silicon dioxide deposited on the conductive oxide layer; andAttorney Docket: 222204-2870 the conductive layer is coupled to a top surface of the conductive oxide layer, a top surface of a gold layer of the alternating nanoscale layers of gold and silicon dioxide, and a side surface of each gold and silicon dioxide layer of the alternating nanoscale layers of gold and silicon dioxide.

19. The nano-optoelectrode device of claim 18, wherein the nanocavity plasmonic hotspot comprises exposed side surfaces of the alternating nanoscale layers of gold and silicon dioxide, each of the exposed side surfaces being different from the top surface of the gold layer of the alternating nanoscale layers of gold and silicon dioxide and different from the side surface of each gold and silicon dioxide layer of the alternating nanoscale layers of gold and silicon dioxide.

20. The nano-optoelectrode device of claim 16,wherein: the portion of each layer of the alternating nanoscale layers of the metal material and the insulator material where the conductive layer is coupled is different from the exposed portions of the alternating nanoscale layers of the metal material and the insulator material where the nanocavity plasmonic hotspot is located; and the nanostructure and the nanocavity plasmonic hotspot are optically and electrically coupled to the conductive substrate at least in part by way of the conductive layer.

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