Carbon Microelectrode Arrays Research Articles

Stable in-vivo electrochemical sensing of tonic serotonin levels using PEDOT/CNT-coated glassy carbon flexible microelectrode arrays.

Chronic sampling of tonic serotonin (5-hydroxytryptamine, 5-HT) concentrations in the brain is critical for tracking neurological disease development and the time course of pharmacological treatments. Despite their value, in vivo chronic multi-site measurements of tonic 5-HT have not been reported. To fill this technological gap, we batch-fabricated implantable glassy carbon (GC) microelectrode arrays (MEAs) onto a flexible SU-8 substrate to provide an electrochemically stable and biocompatible device/tissue interface. To achieve detection of tonic 5-HT concentrations, we applied a poly(3,4-ethylenedioxythiophene)/carbon nanotube (PEDOT/CNT) electrode coating and optimized a square wave voltammetry (SWV) waveform for selective 5-HT measurement. In vitro, the PEDOT/CNT-coated GC microelectrodes achieved high sensitivity to 5-HT, good fouling resistance, and excellent selectivity against the most common neurochemical interferents. In vivo, our PEDOT/CNT-coated GC MEAs successfully detected basal 5-HT concentrations at different locations within the CA2 region of the hippocampus of both anesthetized and awake mice. Furthermore, the PEDOT/CNT-coated MEAs were able to detect tonic 5-HT in the mouse hippocampus for one week after implantation. Histology reveals that the flexible GC MEA implants caused less tissue damage and reduced inflammatory response in the hippocampus compared to commercially available stiff silicon probes. To the best of our knowledge, this PEDOT/CNT-coated GC MEA is the first implantable, flexible sensor capable of chronic in vivo multi-site sensing of tonic 5-HT.

(Digital Presentation) Fabrication and Characterization of C-MEMS Based 3-Dimensional Microelectrode Arrays for Cardiac Electrophysiological Studies

In-vitro examination of the electrical conduction characteristics and the beating of cardiomyocytes can be done using Microelectrode arrays(MEAs). The microelectrodes continuously monitor the electrical activity of the active cardiac cells on a microsecond timescale and presents a precise data based on that. Since the introduction of MEAs, many efforts have been made by scientists to evolve this technology by means of microfabrication. Previously, planar metallic electrodes were mostly used for this study but they could not penetrate the dead cells and reach the active cell layers. To overcome this, protruding 3-D microelectrodes were introduced that could puncture the dead tissues and reach the active cells for effective recording of cardiac electrical potentials.The characteristics of an electrode are defined by the characteristics of the material used to develop it. In this paper, we focus on the fabrication of cylindrical 3-dimensional Glassy Carbon microelectrode arrays (MEAs) for analyzing cell preparations from cardiac tissues. In order to improve the electrical properties of the commercially available electrodes, we have used a highly conductive material for fabrication. Glassy Carbon microelectrodes were fabricated by the pyrolysis of SU-8 microelectrodes which were developed by a standard lithographic process on Silicon wafer. The ohmic nature and high conductivity of Glassy Carbon makes it a suitable material to be implemented in electrophysiological studies. Further in our work, we have performed the theoretical and structural analysis using Comsol Multiphysics 5.2 considering different geometries of microelectrodes. The skin insertion force is calculated to be 0.012N, which is much lesser than the comprehensive force (15.38N), the maximum bending force (0.885N) and the maximum buckling force (3.28N) per cylindrical microelectrode. The maximum Von Mises stress (as shown in the figure) acting at the base where it is attached to the substrate is found out to be 6.56x106 N/m2 for each cylindrical microneedle. Among all the considered geometries, it can be concluded that the fabricated cylindrical microelectrodes penetrate successfully without breaking or bending and causing minimal damage to the cardiac tissues. The slanted tip microelectrode was also favored as it’s design makes it able to easily pierce the cardiac cell layers. However, the Maximum Von Mises stress distribution showed that the stress at the tip was much higher than the Yield strength of Glassy Carbon (4Gpa) making it evident that the tip might break while penetrating. With the theoretical and simulation analysis performed we were thus able to optimize the geometry and establish that Glassy Carbon proves to be a good material for fabrication of 3D microelectrode arrays. Figure 1

In situ graphene-modified carbon microelectrode array biosensor for biofilm impedance analysis

Microbial films, formed by the microorganisms to adapt to their living environment, are closely related to the drug resistance and persistent infection of certain diseases such as gingivitis. Impedimetric biosensors could provide an effective means to study the biofilm formation and screening antibiofilm drugs, their performance is closely dependent on the interface materials used thereon. Here, we report a sensitive biosensor platform for this purpose by integration of graphene with carbon microelectrode arrays (C-MEA). A C-MEA was obtained on a silicon substrate through photolithography and subsequent pyrolysis. Characterized by scanning electron microscopy (SEM), Raman spectra, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and electrochemical, we verified that the C-MEAs could evolve into an electrochemically in situ graphene-modified form, GC-MEAs. Using GC-MEA, the growth of biofilm of S. mutans was successfully monitored. Compared to C-MEAs and conventional macrosized counterparts, significant impedance signal amplification and wider detectable frequency range were achieved on the GC-MEAs. Besides, we demonstrated the impedance sensing technology presents high specificity towards the interface-stacked biofilm. The increase in impedimetric signal on the GC-MEAs was 1.4∼2.1 times stronger than that of the C-MEAs and 12.2–13.9 times that of the macrosized electrodes with biofilm growth at a detection frequency of 10.0 kHz. In the last part, the destruction of biofilms grown on the GC-MEAs by using cetylpyridinium chloride was readily monitored by the GC-MEAs senor. In general, graphene-based microelectrode arrays show promise for developing high-throughput drug screening platforms for dealing with detrimental biofilms.

Glassy carbon microelectrode arrays enable voltage-peak separated simultaneous detection of dopamine and serotonin using fast scan cyclic voltammetry.

Progress in real-time, simultaneous in vivo detection of multiple neurotransmitters will help accelerate advances in neuroscience research. The need for development of probes capable of stable electrochemical detection of rapid neurotransmitter fluctuations with high sensitivity and selectivity and sub-second temporal resolution has, therefore, become compelling. Additionally, a higher spatial resolution multi-channel capability is required to capture the complex neurotransmission dynamics across different brain regions. These research needs have inspired the introduction of glassy carbon (GC) microelectrode arrays on flexible polymer substrates through carbon MEMS (C-MEMS) microfabrication process followed by a novel pattern transfer technique. These implantable GC microelectrodes provide unique advantages in electrochemical detection of electroactive neurotransmitters through the presence of active carboxyl, carbonyl, and hydroxyl functional groups. In addition, they offer fast electron transfer kinetics, capacitive electrochemical behavior, and wide electrochemical window. Here, we combine the use of these GC microelectrodes with the fast scan cyclic voltammetry (FSCV) technique to optimize the co-detection of dopamine (DA) and serotonin (5-HT) in vitro and in vivo. We demonstrate that using optimized FSCV triangular waveform at scan rates ≤700 V s-1 and holding and switching at potentials of 0.4 and 1 V respectively, it is possible to discriminate voltage reduction and oxidation peaks of DA and 5-HT, with 5-HT contributing distinct multiple oxidation peaks. Taken together, our results present a compelling case for a carbon-based MEA platform rich with active functional groups that allows for repeatable and stable detection of electroactive multiple neurotransmitters at concentrations as low as 1.1 nM.

A high-energy aqueous on-chip lithium-ion capacitor based on interdigital 3D carbon microelectrode arrays

There is a growing interest in the development of high energy on-chip capacitive energy storage units for application in microelectronic devices. Lithium-ion capacitor (LIC) typically comprising battery-type and capacitor-type electrodes offer the opportunity for an improved energy density in capacitive energy storage. In this work, an aqueous on-chip LIC was fabricated using carbon microelectromechanical systems (C-MEMS) technique. Oxygen plasma-treated 3D carbon microelectrode arrays served as the capacitor-type electrode in the LIC, while LiFePO4 integrated on the 3D carbon microelectrode arrays was used as the battery-type cathode. Electrochemical performance evaluation shows that the aqueous on-chip LIC can deliver an areal density up to ~5.03 μWh cm−2, which is ~5 times higher than the oxygen plasma-treated symmetric carbon microelectrode-based electrochemical capacitor.

Hydrodynamic channeling as a controlled flow reversal mechanism for bidirectional AC electroosmotic pumping using glassy carbon microelectrode arrays

Controlled bidirectional flow by AC electroosmotic means is achieved using asymmetric coplanar and high-aspect-ratio glassy carbon electrodes and without the involvement of moving elements. The forward and backward fluidic propulsion is the result of hydrodynamic channeling of the fluid in a microfluidic device. The asymmetric coplanar electrodes were fabricated by photolithographic patterning of SU-8 photoresist, followed by pyrolysis at 900 °C. Morphological characterization of the carbon structures was carried out by SEM and confocal microscopy. Then, Raman and EDX spectroscopies confirmed that the resulting carbon material is appropriate for electrokinetic applications. A finite element analysis was carried out to study the flow development by AC electroosmosis. Electrode arrays of three different asymmetry ratios (60 µm:20 µm, 80 µm:20 µm, and 100 µm:20 µm) were fabricated and tested. Fluid velocity was measured for an applied bias in the 2–20 VPP amplitude range, and in the 1 kHz to 200 MHz frequency range. Overall maximum measured forward and reverse fluid velocities were 28.59 µm s−1 and 338 µm s−1, respectively. On an additional set of devices with the same asymmetry ratios, a second photolithography step was utilized to produce high-aspect-ratio microposts on top of the coplanar electrodes to study the effect of high electrode contact surface to generate bidirectional flow. Using the same amplitude and frequency ranges as for planar structures in experimental testing, the overall maximum measured velocities were 9.23 µm s−1 and 90.66 µm s−1 for the forward and reverse regimes, respectively. In contrast to the planar electrodes, microposts-containing electrodes had more balanced velocity magnitudes between reverse and forward flows as the asymmetry ratio increases. In this case, the use of this electrode topology can be useful when symmetry of the forward and backward flow is more important than the magnitude of the volumetric flow rate.

Fabrication of surface renewable carbon microelectrode arrays and their application in heavy metal ion sensing

In this paper, surface renewable carbon microelectrode arrays (MEAs) were developed using microfabrication technology and were successfully applied in heavy metal ion sensing.

Plasma etched carbon microelectrode arrays for bioelectrical measurements

Carbon-based materials have attracted much attention in biological applications like interfacing electrodes with neurons and cell growth platforms due to their natural biocompatibility and tailorable material properties. Here we have fabricated sputtered carbon thin film electrodes for bioelectrical measurements. Reactive ion etching (RIE) recipes were optimized with Taguchi method to etch the close field unbalanced magnetron sputtered carbon thin film (nanocarbon, nC) consisting of nanoscale crystalline sp2-domains in amorphous sp3-bonded backbone. Plasma etching processes used gas mixtures of Ar/O2/SF6/CHF3 for RIE and O2/SF6 for ICP-RIE. The highest achieved etch rate for nanocarbon was ≫389 nm/min and best chromium etch mask selectivity was 135:1. Biocompatibility of the material was tested with rat neuronal cultures. Next, we fabricated multielectrode arrays (MEA) with carbon recording electrodes and metal wiring. Organotypic brain slices grown on the MEAs were viable and showed characteristic spontaneous electrical network activity. The results demonstrate that interactions with nanocarbon substrate support neuronal survival and maturation of functional neuronal networks. Thus the material can have wide applications in biomedical research.

Fabrication of SU-8 Based Three-Dimensional Carbon Microelectrodes Array As Anode Material for Lithium Ion Batteries

Introduction The development of three-dimensional (3D) microelectrodes is essential not only to achieve high energy and power density Li-ion batteries but also to minimize the ohmic losses and therefore achieve better performance. In this work, we used SU-8, an epoxy based negative photoresist which yields hard carbon upon pyrolysis for fabricating 3D micro-post arrays as electrodes1. The SU-8 derived 3D carbon microelectrodes on Silicon (Si) wafer has been reported earlier in literature, however the capacity values were quite moderate2. This is due to the high resistance offered by Si wafer used as a collector. Our group reported recently that the gravimetric reversible capacity value may be almost doubled when SU-8 derived carbon film was prepared on stainless steel (SS) wafer as compared to Si wafer. This inspires us further to fabricate 3D carbon microelectrodes array on SS wafer and to test their electrochemical performance. Experimental SU-8 2100 was spin coated on cleaned SS wafer. Prebaking, UV exposure and post-exposure baking conditions were optimized to prepare SU-8 based 3D micropillars with an aspect ratio of 2 (50µm height and 25µm diameter), and 35µm spacing using photolithography. As-obtained micropillars were then pyrolysed under the controlled N2 atmosphere in a tubular furnace at 900ºC to obtain 3D carbon microelectrode arrays. As-fabricated, 3D carbon microelectrode array on SS wafer was used as working electrode while lithium foil as the counter electrode in Swagelok half-cell assembly to test their electrochemical performance using potentiostat/galvanostat. Results and discussions Figure 1a shows the optical profiler image of SU-8 derived 3D carbon microelectrode array. It was observed that the 3D cylindrical morphology was retained after carbonization however there was nearly 50% shrinkage. As-obtained 3D carbon microelectrode arrays were found to have 26µm height, 16µm diameter, and 40µm spacing. Galvanostatic charge-discharge experiments were carried out at 37.2 mA/g current density. These 3D carbon microelectrode arrays have shown a high discharge capacity (~600 mAh/g) even after 165 continuous charge/discharge cycles (Figure 1b). This is significantly higher than the reported values for 3D carbon micropillars on Si wafer2. A comparison of volumetric capacity was also made. Further detailed characterization of these carbon microelectrodes and their electrochemical performance with cyclic voltammetry results will be presented during the conference.

Homogeneous transfer of graphene oxide into photoresist: Fabrication of high surface area three-dimensional micro-arrays by modified photolithography

Herein, we studied the homogeneous transfer of graphene oxide (GO) into photocurable SU-8 photoresist for fabricating GO/SU-8 three-dimensional (3D) composite micropillar arrays by modified photolithography. SU-8 is a negative toned epoxy based photoresist, which includes 8 epoxy groups in each SU-8 monomer. The effects of the concentration of GO flakes on the thermal, mechanical and specific surface area (SSA) properties of the resultant composites were investigated. The large amount of oxygen functional groups on the GO plane and at the edges allowed uniform distribution of GO sheets within the SU-8 resin. The GO/SU-8 micropillar arrays were fabricated by a versatile ultraviolet (UV) photolithography technique that allowed the synthesis of various 3D micro–nano integrated carbon microelectrode arrays. The integrated GO flakes were bonded to the surface or embedded within the primary structure of SU-8 micro-pillars. These SU-8 micropillars having surface-bonded or embedded GO flakes showed superior thermal stability, strength, and SSA characteristics than bare SU-8 micropillars. Thus, this new synthesis approach provides a novel route for developing high performance catalysts, sensors, and adsorbents, among other materials.

In Vivo Dopamine Detection and Single Unit Recordings Using Intracortical Glassy Carbon Microelectrode Arrays.

In this study, we present a 4-channel intracortical glassy carbon (GC) microelectrode array on a flexible substrate for the simultaneous in vivo neural activity recording and dopamine (DA) concentration measurement at four different brain locations (220μm vertical spacing). The ability of GC microelectrodes to detect DA was firstly assessed in vitro in phosphate-buffered saline solution and then validated in vivo measuring spontaneous DA concentration in the Striatum of European Starling songbird through fast scan cyclic voltammetry (FSCV). The capability of GC microelectrode arrays and commercial penetrating metal microelectrode arrays to record neural activity from the Caudomedial Neostriatum of European starling songbird was compared. Preliminary results demonstrated the ability of GC microelectrodes in detecting neurotransmitters release and recording neural activity in vivo. GC microelectrodes array may, therefore, offer a new opportunity to understand the intimate relations linking electrophysiological parameters with neurotransmitters release.

Multilayer poly(3,4-ethylenedioxythiophene)-dexamethasone and poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate-carbon nanotubes coatings on glassy carbon microelectrode arrays for controlled drug release.

The authors present an electrochemically controlled, drug releasing neural interface composed of a glassy carbon (GC) microelectrode array combined with a multilayer poly(3,4-ethylenedioxythiophene) (PEDOT) coating. The system integrates the high stability of the GC electrode substrate, ideal for electrical stimulation and electrochemical detection of neurotransmitters, with the on-demand drug-releasing capabilities of PEDOT-dexamethasone compound, through a mechanically stable interlayer of PEDOT-polystyrene sulfonate (PSS)-carbon nanotubes (CNT). The authors demonstrate that such interlayer improves both the mechanical and electrochemical properties of the neural interface, when compared with a single PEDOT-dexamethasone coating. Moreover, the multilayer coating is able to withstand 10 × 106 biphasic pulses and delamination test with negligible change to the impedance spectra. Cross-section scanning electron microscopy images support that the PEDOT-PSS-CNT interlayer significantly improves the adhesion between the GC substrate and PEDOT-dexamethasone coating, showing no discontinuities between the three well-interconnected layers. Furthermore, the multilayer coating has superior electrochemical properties, in terms of impedance and charge transfer capabilities as compared to a single layer of either PEDOT coating or the GC substrate alone. The authors verified the drug releasing capabilities of the PEDOT-dexamethasone layer when integrated into the multilayer interface through repeated stimulation protocols in vitro, and found a pharmacologically relevant release of dexamethasone.

Notes on Neuroplasticity Investigation using Coupled Electrical and Electrochemical Sensing through Carbon Electrodes

Neuroplasticity, the ability of the brain to form new neural pathways and synaptic connections, is gaining renewed interest for therapeutic purposes in stroke or spinal cord injury patients. Earlier work in this area in animal models has shown that behavior modulation was associated with the release of serotonin that subsequently leads to changes in gene expression and new neural growth [1]. A separate work has also demonstrated that using serotonin 1A agonists in rats with respiratory dysfunction due spinal cord injury results in better respiratory function [2]. Taken together, these studies indicate that neurotransmitters such as serotonin are closely linked to neuroplasticity, suggesting that changes in levels of these neurotransmitters can be correlated to synaptic changes. Currently, there is growing interest in the use of electrical stimulation as a means for inducing neuroplasticity in stroke and spinal cord injury patients [3]. However, while the data suggests that plasticity could be induced by electrical stimulation, neither the mechanism nor the protocols of stimulation are understood. We submit that a possible path to understanding these mechanisms involves simultaneous real-time monitoring of neurotransmitters such as serotonin electrochemically and electrical signals during stimulation and finding a correlation between these electrical signals and neurotransmitters. In cases where detection of several key electroactive neurotransmitters like serotonin and dopamine is sought, fast scan cyclic voltammetry (FSCV) with its high temporal resolution is the preferred electrochemical method of obtaining real time data [4]. Now, to be able to simultaneously monitor these electrochemical signals along with electrical signals, new approaches in neural probe material and architecture selection are required, as almost all neural probes currently in use are capable of recording only electrical or chemical signals, but not both. Thus, implementation of electrochemical monitoring techniques in animal models requires an integrated electrode array with a size suitable for an animal containing a counter electrode, working electrodes and a reference electrode. Furthermore, electrode materials capable of electrochemically detecting the presence of neurotransmitters without undergoing non-reversible reactions are sought. To meet this need, we investigate and report on the use of glassy carbon, a form of carbon that has been demonstrated to possess ideal characteristics, such as a wide electrochemical window with no irreversible reactions as a coupled electrical and electrochemical sensing platform. In this particular study, we introduce a 12-channel glassy carbon (GC) microelectrode array fabricated on a flexible substrate. The specific design introduced here consists of electrodes supported on a polyimide substrate with penetrating probes at their edges that can penetrate up to 1.25 mm into an animal's cortex or spinal cord. Each probe contains a glassy carbon electrode that can be used to detect serotonin, stimulate a neuron, or read an electrophysiological signal. Our preliminary results show that serotonin can be detected using a polyimide-glassy carbon device down to at least 1 uM in vitro by stimulating through one portion of the device and reading through another (Figure 1). Furthermore, we have shown that our electrodes can read electrophysiological data in-vivo. Figure 2b shows the Fourier Transform of a few seconds of electrical brain signals from a song bird without stimulus. In this graph low frequency alpha waves are most prominent. Figure 2c, the stimulus graph, on the other hand, shows that the beta and gamma waves became more prominent under external, audio stimulation. We believe that the ability to couple this kind of electrical signal detection with electrochemical sensing through FSCV (fast-scan CV) in a single device for in-vivostudies give promise for the disambiguation behind the mechanisms involved in neuroplasticity. Figure 1: Background subtracted cyclic voltagramms for various concentrations of serotonin Figure2: In vivo ECoG signals recorded with carbon electrodes. (a) Time lapse of the audio stimulus (b) Amplitude spectra of the animal during quiet time (c) Amplitude spectra of the signal during the stimulus phase. [1] Kandel, Eric R. Science 294, no. 5544 (2001): 1030-1038. [2] Choi, Howard, Wei-Lee Liao, Kimberly M. Newton, Renna C. Onario, Allyson M. King, Federico C. Desilets, Eric J. Woodard et al. The Journal of neuroscience 25, no. 18 (2005): 4550-4559. [3] Dimyan, Michael A., and Leonardo G. Cohen. Nature Reviews Neurology 7, no. 2 (2011): 76-85. [4] Lama, Rinchen D., Karl Charlson, Arun Anantharam, and Parastoo Hashemi. Analytical chemistry 84, no. 19 (2012): 8096-8101. Figure 1

In-Vivo Characterization of Glassy Carbon µ-Electrodes and Histological Analysis of Brain Tissue after Chronic Implants

For neural applications, materials that combine excellent electromechanical properties with long-term (> 5 years) and high fidelity performance capabilities have not yet been reported. Good electrodes should not only be able to adapt to eventual physiological changes in the body (e.g. inflammatory responses), but also able to perform without damaging the host tissue. The combination of these two characteristics is difficult to accomplish, because the ability of a material to undergo changes is often accompanied by the formation of reaction products that might interact with the surrounding tissue, and eventually harm it. Glassy carbon is a biocompatible and electrochemically inert material with tunable mechanical and electrical properties, high charge injection capacity and great resistance to corrosion. These merits motivate the use of glassy carbon for neural applications, and in particular for the realization of electrocorticography (ECoG) microelectrodes that can sense and stimulate brain activity. Thus we propose to replace the commonly used noble metals like platinum, gold and iridium, with glassy carbon to improve the performances of traditional neural prostheses, thanks to better charge transfer capabilities and higher electrochemical stability. This investigation specifically reports characterization of glassy carbon microelectrode arrays (MEAs) used to sense and stimulate neural activity. Further, we report on key findings in long-term effects based on histological analysis of the brain tissue after chronic implants. Significant focus is given in this work to the investigation of tissue responses of motor cortex after 6 weeks of implantation, and to materials degradation of chronic in-vivo implants. In-vivo long-term impedance measurements and brain activity recordings are also performed to test the functionality of the neural devices and reported here.

Suspended integration of pyrolytic carbon membrane on C-MEMS

Pyrolytic carbon materials contain high internal surface area, desirable pore structure, and controlled surface functionalities, making them effective for gas purification, separation, storage, and chemical reactions. This research describes a two-step (i.e., photolithography and pyrolysis) procedure to integrate suspended porous carbon membranes on C-MEMS from SU-8 photolithography precursor. The suspended SU-8 film was first generated simultaneously with micro-post array during lithography through controlling exposure parameters. A followed pyrolyzing process converted the structure into carbon microelectrode array with the pyrolytic membrane on top of it. It was demonstrated that stress generated during pyrolysis could be applied to control the porosity of membrane, and such high-porosity membrane can find various applications, especially in the field of filtration, selective gas permeation and carbon microreactors. The electrochemical property of this integrated structure has been explored through cyclic voltammetric measurements. It shows that the specific capacitance increase of almost four times after the pyrolytic carbon membrane integration, which indicates its potential use in energy-related fields.

Surface Engineered Pyrolyzed Carbon Electrode Arrays for Bio-Sensing

There is urgent need to develop highly selective, sensitive and reproducible miniaturized bio-sensing platform based on reliable interface that is compatible with microfabrication processing. Our research objective is to advance fundamental research by fabricating pyrolyzed carbon arrays with high surface area as a bio-sensing electrode, developing the functionalization methods to increasing biomolecules immobilization efficiency and further understanding electrochemical phenomena occurring at bio/carbon interfaces. The carbon microelectrode arrays with high aspect ratio and porous surface have been fabricated by carbon microelectromechanical systems (C-MEMS) while the nanomaterials such as graphene have been integrated to further increase surface area. To achieve the efficient covalent immobilization of biomolecules, various oxidation and reduction functionalization methods have been investigated. The oxidation treatment we used in this study includes vacuum ultraviolet, electrochemical activation, UV/Ozone and oxygen RIE. The reduction treatment includes direct amination and diazonium grafting. The functionalized surface has been characterized using XPS, CV and FTIR to confirm and calculate the surface coverage of different functional groups. The developed bio-sensing platform was then applied for several applications, such as: DNA sensor; Glucose sensor; H2O2 sensor; Aptamer sensor and HIV sensor. The performance and sensitivity of each biosensor will be discussed in the talk.

C-MEMS Based Microsupercapacitors and Microsensors

The rapid development of miniaturized electronic devices has led to a growing need for rechargeable micro-power sources with high performances. Miniaturized micro-supercapacitors have great potential to replace batteries and electrolytic capacitors in different types of applications. Carbon microelectromechanical systems (C-MEMS) technique, in which patterned photoresist is pyrolyzed in an inert environment at a high temperature is a powerful approach to fabricate high aspect ratio carbon microelectrode arrays, which could be a promising platform for various micro-power applications. To further improve the electrochemical properties of the carbon microelectrodes, different nanomaterials could be integrated by electrostatic spray deposition (ESD). This review provides an overview of our research at FIU on micro-supercapacitors with different structural designs and active materials.

Growth of nano-wrinkles on photoresist-derived carbon microelectrode array

A novel fabrication method for integrating nano-wrinkles to carbon microelectromechanical systems (C-MEMS) posts on a silicon substrate is proposed in this paper. In the fabrication of carbon microelectrode array, SU-8, a negative photoresist is patterned by photolithography and subsequently pyrolysed at high temperatures in an oxygen-free environment. In this process, the SU-8 posts are slowly converted to the desired carbon posts with properties resembling those of glassy carbon, and the carbon posts have shrinkage in both vertical and radial directions. As we deposit a thin layer (nanoscale order) of carbon before pyrolysis, nano-wrinkle patterns can be generated with the shrinking of the photoresist due to a large difference in the elastic moduli as well as high compressive stress. The nano-wrinkles generated in carbon films can greatly enlarge specific surface area, which significantly enhances the electrochemical performance compared to the blank posts. Since the carbon nano-wrinkles have the same nature as the carbon posts, the stability and biological compatibility of nano-wrinkles integrated microelectrodes are greatly enhanced.

Stress-Driven and Carbon-Assisted Growth of $ \hbox{SiO}_{x}\hbox{N}_{y}$ Nanowires on Photoresist-Derived Carbon Microelectrode

An integration strategy is devised for a reliable, scalable, and catalyst-free assembly of SiOxNy nanowires in photoresist-derived carbon microelectrodes. The approach involved UV photolithography process of SU8 photoresist, followed by high-temperature carbonization, and was versatile in yielding various 3-D micro-nano integrated carbon microelectrode arrays (CMEAs). The morphology of the SiOxNy nanowires and the nanowire-integrated CMEA was characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The chemical composition of the SiOxNy nanowires was confirmed by energy-dispersive X-ray and X-ray photoelectron spectroscopy. A synergetic growth mechanism is proposed based on our experimental observations, in which both carbon-assisted and stress-driven mechanisms were identified to interpret the formation of SiOxNy nanowires. Further study revealed that the nanowire-integrated 3-D CMEA showed improved electrical and electrochemical performances than the blank ones, demonstrating potential applications in electrochemical, biological, and energy-related fields. Meanwhile, the developed method represents a low-cost and easy way to mass production of SiOxNy nanowire-integrated CMEA.

Concentration gradient induced morphology evolution of silica nanostructure growth on photoresist-derived carbon micropatterns

The evolution of silica nanostructure morphology induced by local Si vapor source concentration gradient has been investigated by a smart design of experiments. Silica nanostructure or their assemblies with different morphologies are obtained on photoresist-derived three-dimensional carbon microelectrode array. At a temperature of 1,000°C, rope-, feather-, and octopus-like nanowire assemblies can be obtained along with the Si vapor source concentration gradient flow. While at 950°C, stringlike assemblies, bamboo-like nanostructures with large joints, and hollow structures with smaller sizes can be obtained along with the Si vapor source concentration gradient flow. Both vapor–liquid-solid and vapor-quasiliquid-solid growth mechanisms have been applied to explain the diverse morphologies involving branching, connecting, and batch growth behaviors. The present approach offers a potential method for precise design and controlled synthesis of nanostructures with different features.