Carbon Microelectrode Arrays Research Articles

Spirally oriented Au microelectrode array sensor for detection of Hg (II)

A simple and reproducible carbon microelectrode array (CMA), designed to eliminate diffusive interference among the microelectrodes, has been fabricated and used as a frame to build a gold (Au) microelectrode array (GMA) sensor. To prepare the CMA initially, rather than use an uncontrollable large number of carbon fibers, only 60 carbon fibers of regular size were used to ensure manageable and reproducible arrangement for array construction. In addition, for efficient spatial arrangement of the microelectrode and easy sensor preparation, carbon fibers were oriented in a spiral fashion by rolling around a Cu wire. The distance between carbon fibers was carefully determined to avoid overlap among individual diffusion layers, one of the important factors governing steady-state current response and sensor-to-sensor reproducibility. After the preparation of a spirally arranged CMA, Au was electrochemically deposited on the surface of individual carbon electrodes to build a final GMA sensor. Then, the GMA sensor was used to measure Hg2+ in a low concentration range. Simultaneously, multiple GMA sensors were independently prepared to examine reproducibility in sensor fabrication as well as electrochemical measurement (sensor-to-sensor reproducibility). Overall, highly sensitive detection of Hg2+ was possible using the proposed GMA sensor due to efficient arrangement of microelectrodes and the sensor-to-sensor reproducibility was superior owing to simplicity in sensor fabrication.

Carbon-Ring Microelectrode Arrays for Electrochemical Imaging of Single Cell Exocytosis: Fabrication and Characterization

Fabrication of carbon microelectrode arrays, with up to 15 electrodes in total tips as small as 10-50 μm, is presented. The support structures of microelectrodes were obtained by pulling multiple quartz capillaries together to form hollow capillary arrays before carbon deposition. Carbon ring microelectrodes were deposited by pyrolysis of acetylene in the lumen of these quartz capillary arrays. Each carbon deposited array tip was filled with epoxy, followed by beveling of the tip of the array to form a deposited carbon-ring microelectrode array (CRMA). Both the number of the microelectrodes in the array and the tip size are independently tunable. These CRMAs have been characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, and electrogenerated chemiluminescence. Additionally, the electrochemical properties were investigated with steady-state voltammetry. In order to demonstrate the utility of these fabricated microelectrodes in neurochemistry, CRMAs containing eight microring electrodes were used for electrochemical monitoring of exocytotic events from single PC12 cells. Subcellular temporal heterogeneities in exocytosis (i.e. cold spots vs hot spots) were successfully detected with the CRMAs.

Optimal Design of 3-D Carbon Microelectrode Array for Dielectrophoretic Manipulation of Nanoparticles in Fluids

Manipulation of nanoparticles using nonuniform electric fields is an area of growing interest for nanotechnology applications. This article presents a design methodology and numerical analysis of electric fields and dielectrophoretic forces for 3-dimensional (3-D) carbon microelectrode array, overcoming the limitations of previous approaches. A description of the boundary element method is developed to compute electric field distribution much precisely. The effects of electrode shape, spacing, width and height on field distribution are considered. The results show that the gradient magnitude produced by square column electrodes is most effective to realize manipulation of nanoparticles in fluids. As both the electrode spacing and width are reduced the field gradient magnitude increases exponentially. By increasing the height of electrodes, the electric field extends largely in the electrode locality, which is advantageous to improve the manipulation efficiency with high degree of precision, flexibility and throughput. The theoretical predictions will provide design guides for 3-D carbon microelectrode array towards manipulation of nanoparticles in fluids, which have been shown in reasonable agreement with literature experimental reports.

Carbon nanotube integrated 3-dimensional carbon microelectrode array by modified SU-8 photoresist photolithography and pyrolysis

An integration strategy is devised for a reliable and scalable assembly of carbon nanotubes in photoresist-derived glassy-like carbon microelectrodes. The approach involves UV photolithography process with carbon nanotube monodispersed photoresist followed by high temperature pyrolysis process, and is versatile in yielding various 3-dimensional micro-nano integrated carbon microelectrode arrays. The morphology of the micro-nano integrated structures is characterized. The integrated microelectrodes demonstrate better electrical performance than the blank microelectrodes, showing potential applications in high-sensitive chemical and biological detection systems. The developed method represents a low-cost and facile way to mass production of carbon nanotube-integrated carbon microelectrode array.

Trapping and Manipulation of Bioparticles by a 3-D Optimal Multiple-Designed Offset Carbon-Microelectrode Array in C-MEMS Fabrication

A dielectrophoretic approach with latest developed three-dimensional (3-D) carbon micro-electro-mechanical system (C-MEMS) has been extended as a potential route with idyllic solution to recommend a low-cost, biocompatible and high throughput manipulation and positioning for bio-particles as compared to 2D-planar microelectrodes. Presented in this paper is a novel platform for modelling and simulation of C-MEMS microfabrication process for dielectrophoresis (DEP) force based on various 3-D offset-microelectrode configurations. Numerical solutions are employed to investigate the upshots of multi-designed microelectrodes, applied voltage, electrode edge-to-edge gap and geometric size of microelectrodes on the electric field intensity gradient, induced by an AC voltage for the deployment of broad categories of bioparticles creation, utilization and their manipulation (separation, concentration, transportation and focusing). Sharp edge electrodes are the principle focus of this paper for DEP manipulation that is more convenient to enhance the electric field intensity distribution. The results show that square column electrodes configuration comparatively create large gradient magnitude in electric field intensity as compared to all other configurations. It is also observed that electric field extends drastically with increases in microelectrode height. These findings are consistent with literature experimental reports and will provide vital strategy for optimal design of DEP devices with 3-D C-MEMS.

Electrochemically activated carbon micro-electrode arrays for electrochemical micro-capacitors

Interdigitated carbon micro-electrode arrays for micro-capacitors are fabricated through the carbon microelectromechanical systems (C-MEMS) technique which is based on the carbonization of patterned photoresist. To improve the capacitive behavior, electrochemical activation is performed on carbon micro-electrode arrays. Cyclic voltammetry (CV) and galvanostatic charge–discharge results demonstrate that the electrochemical activation effectively increases the capacitance of the micro-electrode arrays by three orders of magnitude. Although the charge–discharge experiments show the non-ideal behavior of micro-capacitors, the specific geometric capacitance reaches as high as 75 mF cm −2 at a scan rate of 5 mV s −1 after electrochemical activation for 30 min. The capacitance loss is less than 13% after 1000 CV cycles. These results indicate that electrochemically activated C-MEMS micro-electrode arrays are promising candidates for on-chip electrochemical micro-capacitor application.

An optimized process for fabrication of high-aspect-ratio photoresist-derived carbon microelectrode array on silicon substrate

An optimized process was developed for fabrication of high-aspect-ratio photoresist-derived carbon microelectrode array on silicon substrate. This process consisted of conventional photolithography, three-step linear pyrolyzing process and micromechanical interlocking. Comparing with previous two-step pyrolysis, three-step linear pyrolysis process can better preserve the geometry of microstructure during pyrolysis, and micromechanical interlocking was introduced to improve bonding strength between carbon microstructure and substrate. As a result, it can be achieved that high-aspect-ratio carbon microelectrode array remained upright and robustly with substrate. The experimental results confirmed that the optimized process is very effective, and the technology will be helpful for integration of 3-dimensional carbon-based devices in the fields of bioMEMS and electrochemical analysis.

Spatially and Temporally Resolved Single-Cell Exocytosis Utilizing Individually Addressable Carbon Microelectrode Arrays

We report the fabrication and characterization of carbon microelectrode arrays (MEAs) and their application to spatially and temporally resolve neurotransmitter release from single pheochromocytoma (PC12) cells. The carbon MEAs are composed of individually addressable 2.5-mum-radius microdisks embedded in glass. The fabrication involves pulling a multibarrel glass capillary containing a single carbon fiber in each barrel into a sharp tip, followed by beveling the electrode tip to form an array (10-20 microm) of carbon microdisks. This simple fabrication procedure eliminates the need for complicated wiring of the independent electrodes, thus allowing preparation of high-density individually addressable microelectrodes. The carbon MEAs have been characterized using scanning electron microscopy, steady-state and fast-scan voltammetry, and numerical simulations. Amperometric results show that subcellular heterogeneity in single-cell exocytosis can be electrochemically detected with MEAs. These ultrasmall electrochemical probes are suitable for detecting fast chemical events in tight spaces, as well as for developing multifunctional electrochemical microsensors.

Bismuth film electrodes for heavy metals determination

Bismuth film electrodes (BiFEs) have a potential to replace toxic mercury used most frequently for determination of heavy metals (Cd, Pb, Zn) by anodic stripping voltammetry. We prepared a graphite disc electrode (0.5 mm in diameter) from a pencil-lead rod and developed a nitrogen doped diamond-like carbon (NDLC) microelectrode array consisting of 50,625 microdiscs with 3 μm in diameter and interelectrode distances of 20 μm on a highly conductive silicon substrate as a support for BiFEs. The disc graphite BiFE was used for simultaneous determination of Pb(II), Cd(II) and Zn(II) by square wave voltammetry (SWV) in an aqueous solution. We found the optimum bismuth-to-metal concentration ratio in the solution to be 20. The dependence of the stripping responses on the concentration of target metals was linear in the range from 1 × 10−8 to 1.2 × 10−7 mol/L. Detection limits 2.4 × 10−9 mol/L for Pb(II), 2.9 × 10−9 mol/L for Cd(II) and 1.2 × 10−8 mol/L for Zn(II) were estimated. A bismuth-plated NDLC microelectrode array was used for Pb(II) determination by differential pulse voltammetry (DPV) in an aqueous solution. We found that the stripping current for bismuth-plated NDLC array was linear in the concentration range of Pb(II) from 2 × 10−8 to 1.2 × 10−7 mol/L. The detection limit 2.2 × 10−8 mol/L was estimated from a calibration plot.

Determination of heavy metals by a mercury-plated diamondlike carbon microelectrode array

Mercury-plated as well as bare nitrogenated diamond-like carbon (NDLC) microelectrode arrays have been investigated for application in in-situ determination of heavy metals (Cu, Pb and Cd) by differential pulse anodic stripping voltammetry (DPASV). A microelectrode array consisting of 50 625 microdiscs with 3 μm in diameter and interelectrode distances of 20 μm was fabricated on a highly conductive silicon substrate and characterized by CV measurements. Current responses of all metals were linear for metal concentrations in the range of 1.6 × 10−8 to 8.3 × 10−8 mol/L and preconcentration time 5 min. The stripping current responses of the bare microelectrode array reached under the same conditions were much lower in comparison with a mercury-plated array. A strong effect upon stripping current responses of metals was observed of adding a small amount of thiocyanate (2 × 10−3 mol/L) into the plating solution.

C-MEMS for the Manufacture of 3D Microbatteries

We have demonstrated that carbon-microelectromechanical systems (C-MEMS), in which patterned photoresist is pyrolyzed in inert environment at high temperature, constitutes a powerful approach to building 3D carbon microelectrode arrays for 3D microbattery applications. High aspect ratio carbon posts (>10:1) are achieved by pyrolyzing SU-8 negative photoresist in a simple one step process. Lithium can be reversibly charged and discharged into these C-MEMS electrodes. Because of the additional volume of the posts, higher capacities are achieved with the 3D array electrodes as compared to unpatterned carbon films with the same projected electrode area. These novel electrode arrays represent one of the critical components for 3D batteries, which may be interconnected with C-MEMS leads to enable smart power management schemes.

Fabrication and Characterization of Sputtered-Carbon Microelectrode Arrays

This paper describes a robust and reliable process for fabricating a novel sputter-deposited, thin-film carbon microelectrode array using standard integrated circuit technologies and silicon micromachining. Sputter-deposited carbon films were investigated as potential candidates for microelectrode materials. The surface properties and cross section of the microelectrode arrays were studied by atomic force microscopy and scanning electron microscopy, respectively. Electrical site impedance, crosstalk, and lifetime (dielectric integrity) of microelectrodes in the array were characterized. Electrochemical response of the microelectrodes to hexaammineruthenium(III) chloride and dopamine were investigated by fast-scan cyclic voltammetry and high-speed, computer-based chronoamperometry; results show that thin-film carbon microelectrodes are well-behaved electrochemically. The thin carbon films offer extremely good electrical, mechanical, and chemical properties and thus qualify as viable candidates for various electroanalytical applications, particularly acute neurophysiological studies.

Electrochemical characterization of a microcellular carbon foam/epoxy composite electrode

The construction of a microcellular carbon foam/epoxy resin composite electrode is described. The large perimeter-to-area ratio (P/A) of the resulting microelectrode array is desirable and represents an improvement in P/A over that of many composites presently in use. The array is characterized by using chronoamperometry and cyclic voltammetry. The results are compared to those of both a glassy carbon electrode and microelectrode array theory. The responses obtained are representative of expected behavior. The capacity of the electrode was 2.1 {times} 10{sup 3} {mu}F/cm{sup 2}, 2 orders of magnitude greater than that expected for carbon.