Carbon Microelectromechanical Systems Research Articles

High-power biofuel cells based on three-dimensional reduced graphene oxide/carbon nanotube micro-arrays

Miniaturized enzymatic biofuel cells (EBFCs) with high cell performance are promising candidates for powering next-generation implantable medical devices. Here, we report a closed-loop theoretical and experimental study on a micro EBFC system based on three-dimensional (3D) carbon micropillar arrays coated with reduced graphene oxide (rGO), carbon nanotubes (CNTs), and a biocatalyst composite. The fabrication process of this system combines the top–down carbon microelectromechanical systems (C-MEMS) technique to fabricate the 3D micropillar array platform and bottom–up electrophoretic deposition (EPD) to deposit the reduced rGO/CNTs/enzyme onto the electrode surface. The Michaelis–Menten constant KM of 2.1 mM for glucose oxidase (GOx) on the rGO/CNTs/GOx bioanode was obtained, which is close to the KM for free GOx. Theoretical modelling of the rGO/CNT-based EBFC system via finite element analysis was conducted to predict the cell performance and efficiency. The experimental results from the developed rGO/CNT-based EBFC showed a maximum power density of 196.04 µW cm−2 at 0.61 V, which is approximately twice the maximum power density obtained from the rGO-based EBFC. The experimental power density is noted to be 71.1% of the theoretical value.

Pyrolysis-induced shrinking of three-dimensional structures fabricated by two-photon polymerization: experiment and theoretical model

The introduction of two-photon polymerization (TPP) into the area of Carbon Micro Electromechanical Systems (C-MEMS) has enabled the fabrication of three-dimensional glassy carbon nanostructures with geometries previously unattainable through conventional UV lithography. Pyrolysis of TPP structures conveys a characteristic reduction of feature size—one that should be properly estimated in order to produce carbon microdevices with accuracy. In this work, we studied the volumetric shrinkage of TPP-derived microwires upon pyrolysis at 900 °C. Through this process, photoresist microwires thermally decompose and shrink by as much as 75%, resulting in glassy carbon nanowires with linewidths between 300 and 550 nm. Even after the thermal decomposition induced by the pyrolysis step, the linewidth of the carbon nanowires was found to be dependent on the TPP exposure parameters. We have also found that the thermal stress induced during the pyrolysis step not only results in axial elongation of the nanowires, but also in buckling in the case of slender carbon nanowires (for aspect ratios greater than 30). Furthermore, we show that the calculated residual mass fraction that remains after pyrolysis depends on the characteristic dimensions of the photoresist microwires, a trend that is consistent with several works found in the literature. This phenomenon is explained through a semi-empirical model that estimates the feature size of the carbon structures, serving as a simple guideline for shrinkage evaluation in other designs.

Fabrication of MnO2/carbon micro/nanostructures based on Carbon-MEMS technique on stainless steel substrate for supercapacitive microelectrodes

Fabrication of carbon micro/nanostructures by carbon microelectromechanical systems (carbon-MEMS) technique on conductive substrate stably is of great significance but difficulty, for the poor adhesive property and low -temperature resistance of the substrate. In this study, three-dimensional carbon micro/nanostructures are fabricated on stainless steel (SS) substrate for the first time by carbon-MEMS technique and oxygen plasma etching process without extra conductive layer fabrication process. The effects of oxygen plasma etching time and the height of photoresist array on the morphologies of carbon micro/nanostructures are investigated. The carbon micro/nanostructures were then electrodeposited with manganese dioxide (MnO2) thin film as microelectrodes for supercapacitors, and the electrochemical performances of the microelectrodes were demonstrated. At the current density of 0.05 mA cm−2, the MnO2/carbon micro/nanostructures microelectrode deposited with 5 min show a large specific capacitance of 453.47 F g−1. It also shows excellent long-term cycling stability of ∼94% capacitance retention even after 6000 cycling tests. This study shows that the MnO2/carbon micro/nanostructures microelectrodes have great potential for supercapacitors as micro-energy storage devices, and the proposed approach of fabricating carbon hierarchical micro/nanostructures array on a conductive substrate is promising for large-scale micro/nanostructures manufacturing.

Glassy carbon microneedles\u2014new transdermal drug delivery device derived from a scalable C-MEMS process

Because carbon is the basic element of all life forms and has been successfully applied as a material for medical applications, it is desirable to investigate carbon for drug delivery applications, as well. In this work, we report the fabrication of a hollow carbon microneedle array with flow channels using a conventional carbon-microelectromechanical system (C-MEMS) process. This process utilizes the scalable and irreversible step of pyrolysis, where prepatterned SU-8 microneedles (precursor) are converted to glassy carbon structures in an inert atmosphere at high temperature (900 °C) while retaining their original shape upon shrinkage. Once converted to glassy carbon, the microneedles inherit the unique properties of hardness, biocompatibility, and thermal and chemical resistance associated with this material. A comparative study of hardness and Young’s modulus for carbon microneedles and SU-8 microneedles was performed to evaluate the increased strength of the microneedles induced by the C-MEMS process steps. Structural shrinkage of the carbon microneedles upon pyrolysis was observed and estimated. Material characterizations including energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy were carried out to estimate the atomic percentage of carbon in the microneedle structure and its crystalline nature, respectively. Our investigations confirm that the microneedles are glassy in nature. Compression and bending tests were also performed to determine the maximum forces that the carbon microneedles can withstand, and it was found that these forces were approximately two orders of magnitude higher than the resistive forces presented by skin. A microneedle array was inserted into mouse skin multiple times and was successfully removed without the breakage of any microneedles.

C-MEMS Device for Plasma Separation from Whole Blood

In this work, we report the fabrication of carbon-microelectromechanical system (C-MEMS) based contactless dielectrophoresis chip for the separation of Red Blood Cell (RBC) and plasma from whole blood. Blood is the most important functional body fluid and it is necessary to separate plasma and RBC for common disease diagnosis. Use of centrifugal force and microfilters are the conventional methods for this separation. To make a portable and cost effective device, researchers found a method of geometry driven separation by means of changing the blood flow channel shapes. This method was not popular because of the pressure driven flow of blood in the channel and the need of the apparatus including syringe pump, tubing, etc. Dielectrophoresis is one of the best methods for this application. But the contact dielectrophoresis (sample is in contact with the electrodes) damages the RBC because of the use of high voltage (more than 100V). It may also cause electrochemical effect, bubble formation and joule heating in the sample. In our development, one Indium Tin Oxide (ITO) coated glass was used as the bottom substrate. ITO coated side was used as the bottom electrode and microchannel was made in SU-8 by UV photolithography on the other side of the substrate. In a separate process, SU-8 derived carbon electrode was fabricated on Si/SiO2 substrate using the conventional C-MEMS process and transferred to 200µm thick PDMS layer. This polydimethylsiloxane (PDMS) layer was used to cover the microchannel in such a way that the carbon electrode was on the upper side of the device, aligned with the microchannel. These two electrodes (ITO and carbon) were capacitively coupled with the microchannel. The eletrostatic force is induced in the blood cells flow in the channel upon applying high frequency (1MHz) electric field to the electrodes. When blood flows in the channel, the electrostatic force combines with the capillary force and produces velocity difference between RBC and plasma resulting in their separation. In the preliminary experiment, we observed the separation of RBC and plasma at less than 1Vp-p with 1MHz frequency. Figure 1

Electrostatically Sprayed Manganese Oxide Films – from Pseudocapacitive Charge Storage Materials to 3D Microelectrode Integrands

Electrochemical capacitors or “supercapacitors” essentially bridge the gap between traditional capacitors and rechargeable batteries with their high specific power and moderate energy densities. Commercial supercapacitors typically comprise activated carbon (AC) electrodes, which rely on electrostatic double layer charge storage mechanisms. Pseudocapacitors, on the other hand, benefit from surface redox reactions which lend them superior capacitance than their double layer counterparts. Conducting polymers and transitional metal oxides (TMOs) account for pseudocapacitors in general and among TMOs, manganese oxides have widely been investigated owing to their high specific capacitances, low cost, and environmental benignity. In this work, porous manganese oxide (MnOx) thin films were synthesized via electrostatic spray deposition (ESD) and evaluated as pseudocapacitive electrode materials in aqueous media. Very interestingly, the gravimetric specific capacitance of the ESD based MnOx electrodes underwent a marked enhancement upon electrochemical cycling, from 72Fg-1 to 225Fg-1, with a concomitant improvement in kinetics and conductivity. The change in capacitance and resistivity is attributed to a partial electrochemical phase transformation from the spinel type hausmannite Mn3O4 to the conducting layered birnessite MnO2. Furthermore, the films were able to retain 88.4% of the maximal capacitance after 1000 cycles. Upon verifying the viability of the manganese oxide films for pseudocapacitive applications, the thin films were integrated onto carbon micro-pillars created via carbon microelectromechanical systems (C-MEMS) for examining their application as potential microelectrode candidates. In a symmetric two-electrode cell setup, the MnOx/C-MEMS microelectrodes were able to deliver specific capacitances as high as 0.055 Fcm-2 and stack capacitances as high as 7.4Fcm-3, with maximal stack energy and power densities of 0.51 mWhcm-3 and 28.3 mWcm-3, respectively. The excellent areal capacitance of the MnOx-MEs is attributed to the pseudocapacitive MnOx as well as the three-dimensional architectural framework provided by the carbon micropillars.

Glassy carbon MEMS for novel origami-styled 3D integrated intracortical and epicortical neural probes

We report on a novel technology for microfabricating 3D origami-styled micro electro-mechanical systems (MEMS) structures with glassy carbon (GC) features and a supporting polymer substrate. GC MEMS devices that open to form 3D microstructures are microfabricated from GC patterns that are made through pyrolysis of polymer precursors on high-temperature resisting substrates like silicon or quartz and then transferring the patterned devices to a flexible substrate like polyimide followed by deposition of an insulation layer. The devices on flexible substrate are then folded into 3D form in an origami-fashion.These 3D MEMS devices have tunable mechanical properties that are achieved by selectively varying the thickness of the polymeric substrate and insulation layers at any desired location. This technology opens new possibilities by enabling microfabrication of a variety of 3D GC MEMS structures suited to applications ranging from biochemical sensing to implantable microelectrode arrays. As a demonstration of the technology, a neural signal recording microelectrode array platform that integrates both surface (cortical) and depth (intracortical) GC microelectrodes onto a single flexible thin-film device is introduced.When the device is unfurled, a pre-shaped shank of polyimide automatically comes off the substrate and forms the penetrating part of the device in a 3D fashion. With the advantage of being highly reproducible and batch-fabricated, the device introduced here allows for simultaneous recording of electrophysiological signals from both the brain surface (electrocorticography—ECoG) and depth (single neuron). Our device, therefore, has the potential to elucidate the roles of underlying neurons on the different components of µECoG signals. For in vivo validation of the design capabilities, the recording sites are coated with a poly(3,4-ethylenedioxythiophene)—polystyrene sulfonate—carbon nanotube composite, to improve the electrical conductivity of the electrodes and consequently the quality of the recorded signals. Results show that both µECoG and intracortical arrays were able to acquire neural signals with high-sensitivity that increased with depth, thereby verifying the device functionality.

All-carbon suspended nanowire sensors as a rapid highly-sensitive label-free chemiresistive biosensing platform

Nanowire sensors offer great potential as highly sensitive electrochemical and electronic biosensors because of their small size, high aspect ratios, and electronic properties. Nevertheless, the available methods to fabricate carbon nanowires in a controlled manner remain limited to expensive techniques. This paper presents a simple fabrication technique for sub-100 nm suspended carbon nanowire sensors by integrating electrospinning and photolithography techniques. Carbon Microelectromechanical Systems (C-MEMS) fabrication techniques allow fabrication of high aspect ratio carbon structures by patterning photoresist polymers into desired shapes and subsequent carbonization of resultant structures by pyrolysis. In our sensor platform, suspended nanowires were deposited by electrospinning while photolithography was used to fabricate support structures. We have achieved suspended carbon nanowires with sub-100 nm diameters in this study. The sensor platform was then integrated with a microfluidic chip to form a lab-on-chip device for label-free chemiresistive biosensing. We have investigated this nanoelectronics label-free biosensor's performance towards bacterial sensing by functionalization with Salmonella-specific aptamer probes. The device was tested with varying concentrations of Salmonella Typhimurium to evaluate sensitivity and various other bacteria to investigate specificity. The results showed that the sensor is highly specific and sensitive in detection of Salmonella with a detection limit of 10 CFU mL−1. Moreover, this proposed chemiresistive assay has a reduced turnaround time of 5 min and sample volume requirement of 5 µL which are much less than reported in the literature.

An electrochemical immunosensor based on a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array nanoelectrodes for sensitive cardiac biomarker detection

We developed an electrochemical redox cycling-based immunosensor using a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array (IDA) nanoelectrodes. The carbon structures were fabricated using a simple, cost-effective, and reproducible microfabrication technology known as carbon microelectromechanical systems (C-MEMS). We demonstrated that the 3D sub-micrometer-sized mesh architecture and selective modification of the suspended mesh facilitated the efficient production of large quantities of electrochemical redox species. The electrochemically active surfaces and small size of IDA nanoelectrodes with a 1:1 aspect ratio exhibited high signal amplification resulting from efficient redox cycling of electrochemical species (PAP/PQI) by a factor of ~25. The proposed selective surface modification scheme facilitated efficient redox cycling and exhibited a linear detection range of 0.001–100 ng/mL for cardiac myoglobin (cMyo). The specific detection of cMyo was also achieved in the presence of other interfering species. Moreover, the proposed 3D carbon system-based immunosensor successfully detected as low as ~0.4 pg/mL cMyo in phosphate-buffered saline and human serum.

A highly sensitive gas-sensing platform based on a metal-oxide nanowire forest grown on a suspended carbon nanowire fabricated at a wafer level

This paper presents a highly sensitive gas-sensing platform based on a ZnO nanowire (NW) forest circumferentially grown on a suspended single glassy carbon NW. The fabrication was carried out at a wafer level using only batch fabrication processes including carbon-microelectromechanical systems and the hydrothermal method. The suspended architecture and relatively high elastic modulus of the carbon nanowires facilitates selective functionalization on the suspended NW. The circumferentially distributed NW arrangement enhances the accessibility of gas molecule to the ZnO-NW sensing sites, thus facilitating highly sensitive gas sensing. The suspended architecture also enhances efficient mass transfer from the bulk. This novel suspended three-dimensional (3D) NW-based sensor configuration allows better NO2 gas sensing capabilities in terms of the limit of detection (9.45 ppb, S/N = 3), sensitivity (0.393 ppb−1), and linear sensing range (50–300 ppb) compared to the same type of ZnO-NW-based gas sensor fabricated in contact with the substrate.

Custom-Designed Glassy Carbon Tips for Atomic Force Microscopy.

Glassy carbon is a graphenic form of elemental carbon obtained from pyrolysis of carbon-rich precursor polymers that can be patterned using various lithographic techniques. It is electrically and thermally conductive, mechanically strong, light, corrosion resistant and easy to functionalize. These properties render it very suitable for Carbon-microelectromechanical systems (Carbon-MEMS) and nanoelectromechanical systems (Carbon-NEMS) applications. Here we report on the fabrication and characterization of fully operational, microfabricated glassy carbon nano-tips for Atomic Force Microscopy (AFM). These tips are 3D-printed on to micro-machined silicon cantilevers by Two-Photon Polymerization (2PP) of acrylate-based photopolymers (commercially known as IP-series resists), followed by their carbonization employing controlled pyrolysis, which shrinks the patterned structure by ≥98% in volume. Tip performance and robustness during contact and dynamic AFM modes are validated by morphology and wear tests. The design and pyrolysis process optimization performed for this work indicate which parameters require special attention when IP-series polymers are used for the fabrication of Carbon-MEMS and NEMS. Microstructural characterization of the resulting material confirms that it features a frozen percolated network of graphene sheets accompanied by disordered carbon and voids, similar to typical glassy carbons. The presented facile fabrication method can be employed for obtaining a variety of 3D glassy carbon nanostructures starting from the stereolithographic designs provided by the user.

Development of a Sensitive Electrochemical Enzymatic Reaction-Based Cholesterol Biosensor Using Nano-Sized Carbon Interdigitated Electrodes Decorated with Gold Nanoparticles.

We developed a versatile and highly sensitive biosensor platform. The platform is based on electrochemical-enzymatic redox cycling induced by selective enzyme immobilization on nano-sized carbon interdigitated electrodes (IDEs) decorated with gold nanoparticles (AuNPs). Without resorting to sophisticated nanofabrication technologies, we used batch wafer-level carbon microelectromechanical systems (C-MEMS) processes to fabricate 3D carbon IDEs reproducibly, simply, and cost effectively. In addition, AuNPs were selectively electrodeposited on specific carbon nanoelectrodes; the high surface-to-volume ratio and fast electron transfer ability of AuNPs enhanced the electrochemical signal across these carbon IDEs. Gold nanoparticle characteristics such as size and morphology were reproducibly controlled by modulating the step-potential and time period in the electrodeposition processes. To detect cholesterol selectively using AuNP/carbon IDEs, cholesterol oxidase (ChOx) was selectively immobilized via the electrochemical reduction of the diazonium cation. The sensitivity of the AuNP/carbon IDE-based biosensor was ensured by efficient amplification of the redox mediators, ferricyanide and ferrocyanide, between selectively immobilized enzyme sites and both of the combs of AuNP/carbon IDEs. The presented AuNP/carbon IDE-based cholesterol biosensor exhibited a wide sensing range (0.005–10 mM) and high sensitivity (~993.91 µA mM−1 cm−2; limit of detection (LOD) ~1.28 µM). In addition, the proposed cholesterol biosensor was found to be highly selective for the cholesterol detection.

Electrostatic Spray Deposition-Based Manganese Oxide Films-From Pseudocapacitive Charge Storage Materials to Three-Dimensional Microelectrode Integrands.

In this study, porous manganese oxide (MnOx) thin films were synthesized via electrostatic spray deposition (ESD) and evaluated as pseudocapacitive electrode materials in neutral aqueous media. Very interestingly, the gravimetric specific capacitance of the ESD-based electrodes underwent a marked enhancement upon electrochemical cycling, from 72 F∙g−1 to 225 F∙g−1, with a concomitant improvement in kinetics and conductivity. The change in capacitance and resistivity is attributed to a partial electrochemical phase transformation from the spinel-type hausmannite Mn3O4 to the conducting layered birnessite MnO2. Furthermore, the films were able to retain 88.4% of the maximal capacitance after 1000 cycles. Upon verifying the viability of the manganese oxide films for pseudocapacitive applications, the thin films were integrated onto carbon micro-pillars created via carbon microelectromechanical systems (C-MEMS) for examining their application as potential microelectrode candidates. In a symmetric two-electrode cell setup, the MnOx/C-MEMS microelectrodes were able to deliver specific capacitances as high as 0.055 F∙cm−2 and stack capacitances as high as 7.4 F·cm−3, with maximal stack energy and power densities of 0.51 mWh·cm−3 and 28.3 mW·cm−3, respectively. The excellent areal capacitance of the MnOx-MEs is attributed to the pseudocapacitive MnOx as well as the three-dimensional architectural framework provided by the carbon micro-pillars.

Increase in graphitization and electrical conductivity of glassy carbon nanowires by rapid thermal annealing

Glassy carbon (GC) exhibits numerous desirable properties such as high thermal and chemical stabilities, good hardness, and good thermal and electrical conductivities. Moreover, GC can be manufactured into micro-/nanostructures through the versatile microfabrication technology, or carbon-micro electromechanical systems, which includes polymer patterning and pyrolysis. However, despite these advantages, there are growing demands for enhancing the electrical conductivity of GC, so that it can compensate or be substituted for other carbon allotropes such as graphite, carbon nanotubes, and graphene. In this study, we demonstrated that simple rapid thermal annealing (RTA) can dramatically enhance the electrical conductivity of pyrolyzed GC nanostructures by ∼ 300%. In this research, two different architectures of 1D carbon nanostructures such as a suspended nanowire that was separated from the substrate with a fixed distance and a substrate-bound nanowire were fabricated using conventional UV-lithography and pyrolysis processes, and their conductivity enhancement behaviors via RTA were studied. After the RTA process, the carbon/oxygen content and G-/D-band intensity ratios, which are correlated to the electrical conductivity, were enhanced, depending on the pyrolysis temperature. GC structures pyrolyzed at relatively low temperatures became more electrically conductive after the RTA process owing to their relatively higher oxygen content. This is because carbon atoms interconnected to oxygen atoms tend to align more readily than those corresponding to other carbon compositions because of the graphene healing mechanism. In addition, the architecture of the carbon nanostructures (i.e., whether they were suspended or substrate-bound nanowires) influenced the RTA-induced increase in electrical conductivity; the former showed a greater increase in electrical conductivity owing to its larger portion of well-aligned carbon atoms at the surface compared to the latter carbon structure. This is because graphitization is initiated on the surface and then proceeds to the carbon core in the heat treatment. In addition, tensile stress generated only at the suspended carbon nanowires during the pyrolysis process is assumed to enhance further the electrical conductivity via RTA. For instance, the electrical conductivity of the suspended carbon nanowires formed by pyrolysis at 600 °C was enhanced to ∼59,000 S/m after the RTA process.

Effect of Current Collector and Pyrolysis Temperature on the Electrochemical Performance of Photoresist Derived Carbon Films

SU-8, an epoxy based negative photoresist has been demonstrated as a potential precursor to fabricate thin films and three-dimensional micropatterned arrays in glassy carbon. However, the use of silicon wafer as a substrate cum collector limits their use in real battery devices. In accordance with the commercial lithium ion battery architecture and also owing to enhanced conductivity, we have successfully demonstrated the use of stainless steel (SS) wafer as a current collector to prepare binder free SU-8 derived carbon thin films. Standard carbon microelectromechanical systems (C-MEMS) process parameters were tuned to obtain a uniform, crack-free carbon thin film on SS wafer upon pyrolysis. Further, we varied the final pyrolysis temperature to examine its effect on the microstructure and composition as characterized with X-ray diffraction, Small angle X-ray scattering, Raman spectroscopy and CHNS-O elemental analyzer respectively. The microstructural changes in the carbon films at different pyrolysis temperature were then correlated with their electrochemical performance as investigated using galvanostat charge/discharge experiments, impedance spectroscopy and cyclic voltammetry. Selection of an appropriate current collector and optimizing the pyrolysis temperature yielded excellent cyclic stability and coulombic efficiency with 400 mAh g−1 reversible capacity after 100 cycles, nearly double to as reported in the literature.

Improved conductivity and capacitance of interdigital carbon microelectrodes through integration with carbon nanotubes for micro-supercapacitors

In the last decade, pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors. Although various methods have been investigated to improve the performance of pyrolyzed carbons, such as conductivity, energy storage density and cycling performance, effective methods for the integration and mass-production of pyrolyzed-carbon-based composites on a large scale are lacking. Here, we report the development of an optimized photolithographic technique for the fine micropatterning of photoresist/chitosan-coated carbon nanotube (CHIT-CNT) composite. After subsequent pyrolysis, the fabricated carbon/CHIT-CNT microelectrode-based micro-supercapacitor has a high capacitance (6.09 mF·cm–2) and energy density (4.5 mWh·cm–3) at a scan rate of 10 mV·s–1. Additionally, the micro-supercapacitor has a remarkable long-term cyclability, with 99.9% capacitance retention after 10,000 cyclic voltammetry cycles. This design and microfabrication process allow the application of carbon microelectromechanical system (C-MEMS)-based micro-supercapacitors due to their high potential for enhancing the mechanical and electrochemical performance of micro-supercapacitors.

C-MEMS Based Micro-Power: From Symmetric to Battery-Type Hybrid Microsupercapacitors

Given the rapid boom in development of miniaturized electronic devices, there has been an ever-increasing demand for high performance rechargeable micro-power devices. At the heart of micro-power are microsupercapacitors, which have great potential as standalone power devices or even replace microbatteries depending upon the application. Carbon microelectromechanical systems (C-MEMS) a technique, in which a patterned photoresist is pyrolyzed in order to produce carbon microelectrode platforms, has been proved to be a powerful approach for fabricating high-performance microsupercapacitors. The as-fabricated carbon electrodes can further be electrochemically activated or even decorated with different nanostructures as such carbon nanotubes, graphene or conducting polymers such as polypyrrole (PPy) in order to further enhance the electrochemical performance of the microsupercapacitors. In general, supercapacitors with identical anode and cathode are referred to as “symmetric” while the ones with different anode and cathode are referred to as “asymmetric” or colloquially as “hybrid”. The latter type of capacitor combining a faradaic type battery electrode and an electrochemical double layer type electrode has gained significant scientific interest in recent years. Intuitively such a capacitor would combine the benefits of the two very disparate electrodes, such as a wide operating potential, high power, high energy along with high cycle longevity. In previous works, our group has mostly focused on integrating nanostructures onto C-MEMS platforms for mostly symmetric microsupercapacitors and at present we are focusing on C-MEMS platforms for hybrid battery-type microsupercapacitors. Detailed works will be presented at the conference.

A New Approach for Selective Surface Functionalization of Carbon Electrodes in Biosensing by Plasma Direct-Writing

Carbon electrodes fabricated by Carbon Microelectromechanical systems (C-MEMS) process is known to be chemically inert. Hence, surface functionalization is required for their use as biosensors and electrochemical electrodes. Surface functionalization of carbon electrodes is conventionally performed by oxygen plasma treatment or acid treatments. These methods generally affect the whole surface of electrodes and cannot limit functionalization to only at specific locations on the electrodes. This paper introduces a novel plasma direct-writing technique for selective functionalization of carbon electrodes with carboxylic groups at room temperature and atmospheric pressure. We demonstrated the plasma direct-writing by patterning oxygen functional groups on carbon electrodes derived from pyrolysis of photolithographically patterned photoresist. The resulting surface chemistry is investigated by scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). Functionalization of hydroxyl and carboxyl groups is a first step towards immobilization of DNA or immunoglobulin for carbon based biosensors. Our plasma direct-writing technique not only enables controlled writing of functional groups but also enables control over the degree of functionalization in a simple one step procedure.

Micro Device for Bio-Particle Positioning in a Confined Microfluidic Volume Using Carbon MEMS and Dielectrophoretic Forces

Experiments on micron sized bio particles (bio compatible micro particles, cells) are limited by the manipulation techniques used to position particles in a zone of interest, like the focus point of an optical system, a micro electrode for an electrical measurement, a tridimensional cellular scaffold or a reaction chamber for a chemical process. We introduce a device that would aid in the precise positioning of micron sized bio particles inside a microfluidic channel, using a combination of individually addressable 3D electrodes and planar electrodes based on carbon micro electro mechanical systems (C-MEMS) to induce dielectrophoretic (DEP) forces 1,2. The proposed device uses a series of carbon-based 3D electrodes and a matrix of planar electrodes produced by the pyrolysis of a common photoresist (SU-8) 3. The electrodes are built on a fused silica substrate to enable the view of experiments trough optical microscopy. Our hypothesis consist in that by using the electrodes to exert a pulsed DEP force, coplanar to the substrate by the 3D electrodes and orthogonal to the substrate by the planar electrodes, it is possible to precisely position a bio particle in a confined microfluidic volume at low flow rates 4. These types of electrodes are chosen because they can induce a DEP force by applying small electric potentials (~ 10 V) due to the fact that are immersed in the carrying fluid. Pulsed DEP was selected due to its low cost implementation and because it is able to affect bio particles positions while maintaining their viability 5. The manufacturing process requires the use of traditional techniques of photolithography to 3D pattern photoresist and a carefully tailored pyrolysis process to obtain the desired electrode features 6. In order to validate the device, the resistivity of the carbon films is measured, cyclic voltammetry is used to characterize the electrochemical behavior of the electrodes, electrode half-cell potential stability is tested over time, particle image velocimetry is used to analyze the flow inside the micro channel and the spatial position of a target particle is monitored using optical microscopy while it is manipulated using DEP force 7. Finally, these results are compared with those obtained in the simulation and theoretical design of the proposed micro-platform.

3D Carbon-MEMS a Potent Molecular Recognition Platform for the Detection of DNA Molecule

Deoxyribonucleic acid (DNA) molecule is the building block which architects the genetic materials for development and functioning of most living organisms. The characteristics of the DNA molecule such as stability to the mechanical and thermal stress, universal presence in all tissue or cell and more informative with unique genetic code, makes it very useful for organisms species detection. Furthermore, recent discovery of the structural and functional properties of the DNA molecule extended its application for bio-imaging, bio-diagnostics and sensing for drug delivery. Thus a number of assays have been introduced for the detection of specific DNA target such as real-time polymerase chain reaction assay and molecular fluorophores labelled platforms, but those are suffering for high costing. Furthermore, traditional biological signal detection platform with two-dimensional (2D) patterns and 2D nature electrodes have the drawbacks of lower sensitivity. Microfabrication of 3D carbonaceous structures, carbon-microelectromechanical system (C-MEMS) based on the thermochemical decomposition of patterned organic photoresist at high temperatures in oxygen-free environment, draw recent attention for the detection of DNA. In comparison with fluorescence detection platform on 2D carbon micropatterns, 3D micro arrays not suffer from optical interferences obtained on oxidized silicon substrates. The architectural tools for 3D C-MEMS, such as lithography and pyrolysis facilitate to generate varied carbon structure with different crystallinity, size and shape. Furthermore, integration of certain nanomaterials such as grapheme, carbon nanotubes or nanofibers with C-MEMS can create high surface area for carbon microarray. Thus fabrication of the 3D carbon microarrays with higher surface area increases the loading capability of the biomolecule to improve the sensitivity and performance of the DNA detection platform. Acknowledgement This research is supported by University Malaya Flagship Grant project FL001A-14AET, MOSTI SF020-2014, and Transdisciplinary Research Grant Scheme (TRGS TR002A-2014) from Malaysian Ministry of Higher Education.