Fabrication Of Microelectrodes Research Articles

Fabrication of electrochemical carbon-based microelectrodes using electrohydrodynamic jet printing technique

Due to unique advantages, carbon is widely used as electrode material for electrochemical sensors. In this paper, an efficient method of combining the electrohydrodynamic jet (E-jet) printing with the lift-off process was presented to produce the carbon-based three-electrode plate. The metal pattern was formed by lift-off process. Then the carbon pattern was printed on the metal layer by E-jet. Moreover, a graphene layer was printed on the carbon layer to improve the sensing performance by E-jet and the effect of scanning rate on thickness and density of layer was investigated. At last, an electrochemical sensor was developed with the well-made three-electrode plate and utilized to detect the samples of potassium ferricyanide and nicotinamide adenine dinucleotide. The results showed that a lower anodic peak potential was obtained in the graphene-modified carbon electrode than that of the bare carbon electrode. And in the electrochemical measurement of potassium ferricyanide, the graphene-modified electrode can decrease the potential distance between the anodic peak and the cathodic peak. It implied that the additional graphene-nanosheets can increase the reactive area and the capability of electronic conduction, thereby making the EC reaction easier to occur.

Experimental study on the microelectrodes fabrication using low speed wire electrical discharge turning (LS-WEDT) combined with multiple cutting strategy

This paper aims at giving an insight into the fabrication of ultra-small microelectrodes and micro-cutting tools using the low speed wire electrical discharge turning (LS-WEDT). The multiple cutting strategy divides the microelectrode machining process into rough cut (RC), semi-finishing trim cut (TC) and finishing trim cut (FTC). Experimental results indicated that the breaking and bending microelectrodes are caused primarily by the improper selection of flushing pressure, peak current and open circuit voltage in FTC. The cylindrical microelectrode of 58μm in diameter is successfully fabricated with good surface quality and high machining accuracy. More importantly, the LS-WEDT method can be used to manufacture the microelectrodes and micro-cutting tools with different micro structures by combining with the numerical control technology. The D-shaped cutting tool of 65μm in diameter and the three spiral micro cutting tool are firstly and successfully manufactured by LS-WEDT method.

Fabrication of Micro-electrodes using Liner Block Moving Electrical Discharge Grinding and Characteristics of Micro-hole Machining of Graphene Nanoplatelet-reinforced Al2O3Composites

Fabrication of Micro-electrodes using Liner Block Moving Electrical Discharge Grinding and Characteristics of Micro-hole Machining of Graphene Nanoplatelet-reinforced Al2O3Composites

PEDOT:PSS coated gold nanopillar microelectrodes with ultralow impedance for neural interfaces

Improving the neuron-electrode interface has been a focus of biomedical research for the last decade. Low impedance, high charge storage capacities and small geometrical surface area are desired for excellent recording conditions. A common way to improve this interface is to increase the electrochemically active surface area of the electrode using nanoporous or nanostructured electrode materials. In this paper, the fabrication of microelectrodes with very high aspect ratio gold nanopillars coated with the conducting polymer PEDOT:PSS is presented. The electrodes are simulated, manufactured and studied using scanning electron microscopy, atomic force microscopy, impedance spectroscopy, cyclic voltammetry and neural cell culture experiments. We show that PEDOT:PSS coated nanopillar electrodes have improved capacity, reduced impedance and in-vitro recordings reveal high signal-to-noise ratio. Depending on pillar height the impedance is more than 350 times smaller compared to planar gold electrodes at 1 kHz and reveals an electrode capacity more than 1,000 times higher.

PEDOT:PSS coated gold nanopillar microelectrodes with ultralow impedance for neural interfaces

Improving the neuron-electrode interface has been a focus of biomedical research for the last decade. Low impedance, high charge storage capacities and small geometrical surface area are desired for excellent recording conditions. A common way to improve this interface is to increase the electrochemically active surface area of the electrode using nanoporous or nanostructured electrode materials. In this paper, the fabrication of microelectrodes with very high aspect ratio gold nanopillars coated with the conducting polymer PEDOT:PSS is presented. The electrodes are simulated, manufactured and studied using scanning electron microscopy, atomic force microscopy, impedance spectroscopy, cyclic voltammetry and neural cell culture experiments. We show that PEDOT:PSS coated nanopillar electrodes have improved capacity, reduced impedance and in-vitro recordings reveal high signal-to-noise ratio. Depending on pillar height the impedance is more than 350 times smaller compared to planar gold electrodes at 1 kHz and reveals an electrode capacity more than 1,000 times higher.

Long-Term Stable Adhesion for Conducting Polymers in Biomedical Applications: IrOx and Nanostructured Platinum Solve the Chronic Challenge.

Conducting polymers (CPs) have frequently been described as outstanding coating materials for neural microelectrodes, providing significantly reduced impedance or higher charge injection compared to pure metals. Usability has until now, however, been limited by poor adhesion of polymers like poly(3,4-ethylenedioxythiophene) (PEDOT) to metallic substrates, ultimately precluding long-term applications. The aim of this study was to overcome this weakness of CPs by introducing two novel adhesion improvement strategies that can easily be integrated with standard microelectrode fabrication processes. Iridium Oxide (IrOx) demonstrated exceptional stability for PEDOT coatings, resulting in polymer survival over 10 000 redox cycles and 110 days under accelerated aging conditions at 60 °C. Nanostructured Pt was furthermore introduced as a purely mechanical adhesion promoter providing 10-fold adhesion improvement compared to smooth Pt substrates by simply altering the morphology of Pt. This layer can be realized in a very simple process that is compatible with any electrode design, turning nanostructured Pt into a universal adhesion layer for CP coatings. By the introduction of these adhesion-promoting strategies, the weakness of CP-based neural probes can ultimately be eliminated and true long-term stable use of PEDOT on neural probes will be possible in future electrode generations.

Micro-electrode fabrication processes for micro-EDM drilling and milling: a state-of-the-art review

These days, miniaturized products have a lot of applications in biotechnology, information technology, environmental and medical industries, electric devices, miniaturized machines, and so on. Micro-electrical discharge machining (micro-EDM) is one the most efficient technologies among the nonconventional machining technologies for producing micro-components. Micro-EDM is able to machine tough die materials which cannot be machined by micro-milling. The micro-EDM method has the capability to machine electrical conductive materials with various hardness, strength, and temperature-resistant and complex shapes with accurate dimensions and fine surface roughness. Moreover, it is widely used to produce micro-scale components and structures such as micro-mold, micro-die, micro-probes, micro-tools, fuel nozzles, photo-masks, thin sheet materials, and complex 3D shapes with high accuracy. This paper presents a state-of-the-art review of micro-EDM process as well as the various kinds of micro-electrode and workpiece materials and dielectrics that have been used by previous researchers. In addition, this paper extensively describes and compares various micro-electrode and micro-tool fabrication processes in order to produce precise micro-products. This work is very helpful for the micro-EDM manufacturers and users to select suitable material, dielectric and fabrication processes in researches, and industry applications.

Study on machining 3D micro mould cavities using reciprocating micro ECM with queued foil microelectrodes

The paper proposes a method for processing 3D micro mould cavities using reciprocating micro electrochemical machining (micro ECM) with queued foil microelectrodes. Specifically, the queued foil microelectrodes were machined from 60-μm-thick 304 stainless steel foils via wire electrical discharge machining (WEDM). In addition, both undersurfaces of these foil microelectrodes were sputter coated with SiO2 insulation films. Research on the blind holes machining using single foil microelectrodes indicated that when a NaNO3 electrolyte reached a concentration of 2.5g/L, 50-μm back-off distance, and 9∼30V machining voltage, the inlet width of the micro mould cavity was controllable within 200±10μm, regardless of the machining depth. Moreover, when the machining voltage was 30V, the machining efficiency was observed to be highest. Based on the optimised parameters for blind holes machining with single foil microelectrodes and a machining layer thickness of 70μm, 3D micro mould cavities with a simple blind hole, rectangular island, and semicircular island with a machining depth exceeding 1000μm were obtained using reciprocating micro ECM with queued foil microelectrodes sputter coated with SiO2 insulation film. Compared with 3D micro mould cavities machined using layered electrolytic milling with 1D micro-cylindrical electrode, the cross-section of the 2D microelectrodes exhibited a strong anti-interference property and outstanding efficiency. Compared with unidirectional feeding micro ECM of 3D microelectrode, the fabrication of such 2D microelectrodes was very simple and flow field in micro ECM processing was greatly improved, which can execute the machining of 3D micro mould cavities with a high-aspect-ratio.

Development of new fabrication and measurement techniques of micro-electrodes with high aspect ratio for micro EDM using typical EDM machine

Abstract Micro-electrodes are used for micro holes EDM drilling in miniaturized products. This study represents novel fabricating and measuring processes of high aspect ratio micro-electrodes based on horizontal moving block electrical discharge grinding (horizontal moving BEDG [HM-BEDG]) and gage block with a typical EDM machine, as well as solving the problems that occur during micro-electrode fabrication. The EDM machine has been used as a coordinate measuring machine (CMM) for measuring micro-electrode diameter, where the gage block acts as a probe and the micro-electrode as a workpiece. As a result, a micro-electrode with the highest aspect ratio (over 60.25) was fabricated successfully with 78.19 μm diameter and 4.70 mm length after producing a through micro hole with 134.5 μm diameter on WC Co. As these processes are simple and do not require high investment for special equipment, micro-electrodes can be fabricated and measured for micro EDM drilling and milling in conventional workshops equipped with EDM machines.

(Invited) Silicon Carbide as a Robust Neural Interface

The intracortical neural interface (INI) could be a key component of brain machine interfaces (BMI), devices which offer the possibility of restored physiological neurological functionality for patients suffering from severe trauma to the central or peripheral nervous system. Unfortunately the main components of the INI, microelectrodes, have not shown appropriate long-term reliability due to multiple biological, material, and mechanical issues. Silicon carbide (SiC) is a semiconductor that is completely chemically inert within the physiological environment and can be micromachined using the same methods as with Si microdevices. We are proposing that a SiC material system may provide the improved longevity and reliability for INI devices. The design, fabrication, and preliminary electrical and electrochemical testing of an all-SiC prototype microelectrode array based on 4H-SiC, with an amorphous silicon carbide (a-SiC) insulator, is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary electrochemical data are presented which show that these prototype electrodes display suitable performance.

Development of an all-SiC neuronal interface device

ABSTRACTThe intracortical neural interface (INI) is a key component of brain machine interfaces (BMI) which offer the possibility to restore functions lost by patients due to severe trauma to the central or peripheral nervous system. Unfortunately today’s neural electrodes suffer from a variety of design flaws, mainly the use of non-biocompatible materials based on Si or W with polymer coatings to mask the underlying material. Silicon carbide (SiC) is a semiconductor that has been proven to be highly biocompatible, and this chemically inert, physically robust material system may provide the longevity and reliability needed for the INI community. The design, fabrication, and preliminary testing of a prototype all-SiC planar microelectrode array based on 4H-SiC with an amorphous silicon carbide (a-SiC) insulator is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary data is presented which shows a proof of concept for an all-SiC microelectrode device.

Characterization of copper microelectrodes, following a homemade lithography, technique, and gold electroless deposition

We report the fabrication and characterization of copper microelectrodes obtained by a homemade lithography technique and after gold electroless deposition. For the fabrication, planes consisting of arrays of electrodes (black in color) with bow tie shape were designed and printed on a transparent paper (Canson ltd.). Using an embroidery frame with a silk fabric, a photographic emulsion was spread on the silk and simultaneously pressing the Canson paper on it. The system was introduced into a closed box and exposed with a UV light. The designed electrode templates prevented direct exposition of the UV light over copper films and indelible ink was spread over it. After the ink was dried, the copper film is immersed into ferric acid to attack the uncovered copper parts (where there is no ink). In this way, we obtained copper electrodes with initial gap separation of ~142μm and subsequently, they followed electroless deposition of gold to make the copper electrodes to contact. For the characterization, electrical measurements were performed. They present ohmic resistance values in the order of 106 Ω produced by surface scattering of the electrons within the gold microwire and enhanced by oxidation of the copper electrodes.

Fabrication and Use of Dual‐function Iridium Oxide Coated Gold SECM Tips. An Application to pH Monitoring above a Copper Electrode Surface during Nitrate Reduction.

AbstractThe fabrication of a gold microelectrode modified with iridium oxide film (IrOx) and its use as tip with a dual function in SECM experiments is reported. The defective structure of the coating onto the microelectrode surface was used as strategy to combine the advantages of both amperometric (for current‐distance determination) and potentiometric (for pH sensing) SECM operation modes. Approach curves, using oxygen and hexaammineruthenium(III) as redox mediators, were obtained without significant loss of the performance and reproducibility of the potentiometric pH response. This allowed the precise positioning of the proposed tip above a substrate in SECM experiments and, subsequently, to monitor pH at the substrate surface. The IrOx modified microelectrode was applied successfully in SECM experiments involving the local proton consumption during the nitrate reduction at a copper cathode surface.

Fabrication of high aspect ratio micro electrode by using EDM

The electrical discharge machining (EDM) process inherits characteristics that make it a promising micro-machining technique. Micro electrical discharge machining (micro- EDM) is a derived form of EDM, which is commonly used to manufacture micro and miniature parts and components by using the conventional electrical discharge machining fundamentals. Moving block electro discharge grinding (Moving BEDG) is one of the processes that can be used to fabricate micro-electrode. In this study, a conventional die sinker EDM machine was used to fabricate the micro-electrode. Modifications are made to the moving BEDG, which include changing the direction of movements and control gap in one electrode. Consequently current was controlled due to the use of roughing, semi-finishing and finishing parameters. Finally, a high aspect ratio micro-electrode with a diameter of 110.49μm and length of 6000μm was fabricated.

Scale of Carbon Nanomaterials Affects Neural Outgrowth and Adhesion.

Carbon nanomaterials have become increasingly popular microelectrode materials for neuroscience applications. Here we study how the scale of carbon nanotubes and carbon nanofibers affect neural viability, outgrowth, and adhesion. Carbon nanotubes were deposited on glass coverslips via a layer-by-layer method with polyethylenimine (PEI). Carbonized nanofibers were fabricated by electrospinning SU-8 and pyrolyzing the nanofiber depositions. Additional substrates tested were carbonized and SU-8 thin films and SU-8 nanofibers. Surfaces were O2-plasma treated, coated with varying concentrations of PEI, seeded with E18 rat cortical cells, and examined at 3, 4, and 7 days in vitro (DIV). Neural adhesion was examined at 4 DIV utilizing a parallel plate flow chamber. At 3 DIV, neural viability was lower on the nanofiber and thin film depositions treated with higher PEI concentrations which corresponded with significantly higher zeta potentials (surface charge); this significance was drastically higher on the nanofibers suggesting that the nanostructure may collect more PEI molecules, causing increased toxicity. At 7 DIV, significantly higher neurite outgrowth was observed on SU-8 nanofiber substrates with nanofibers a significant fraction of a neuron's size. No differences were detected for carbonized nanofibers or carbon nanotubes. Both carbonized and SU-8 nanofibers had significantly higher cellular adhesion post-flow in comparison to controls whereas the carbon nanotubes were statistically similar to control substrates. These data suggest a neural cell preference for larger-scale nanomaterials with specific surface treatments. These characteristics could be taken advantage of in the future design and fabrication of neural microelectrodes.

Fabrication of 3D Microelectrodes by Combining Wire Electrochemical Micromachining and Micro-electric Resistance Slip Welding

Micromachining, using microelectrodes, is a key technology for manufacturing three-dimensional (3D) microstructures. However, 3D microelectrodes are difficult to fabricate, 3D microstructures are fabricated mainly using simple-shaped tools microelectrode with a layer by layer scanning strategy. Based on micro double-staged laminated object manufacture (micro-DLOM), 3D microelectrodes can be obtained by combining closed loop middle-speed wire (Ø100∼180μm) electrical discharge machining (WEDM) and thermal diffusion welding. But it is difficult to obtain 3D microelectrodes with an edge length of end face less than 100μm, though by low speed wire electrical discharge machining (LS-WEDM) or femtosecond laser cutting, the dimension of 3D microelectrodes can be further miniaturized, they are both very expensive. To solve the problem above, this paper proposed a low-cost method combining wire (Ø8μm) electrochemical micromachining (WECMM) and micro-electric resistance slip welding to fabricate 3D microelectrodes. Firstly, with WECMM combining low frequency micro-vibration and travelling of wire electrode, 30-μm-thick 0Cr18Ni9 stainless steel foils were cut to obtain multi-layer two-dimensional (2D) microstructures. Secondly, through micro-electric resistance slip welding, the multi-layer 2D microstructures were laminated and bonded to fit 3D microelectrodes. Moreover, this paper investigated the influences of applied voltage, feed speed, wire electrode travelling and micro-vibration on machining surface quality and dimensional accuracy. Based on the studies above, two typical 3D microelectrodes with a dimension less than 100μm were successfully fabricated. Finally, applying the fabricated 3D microelectrodes to micro-electrochemical machining (micro-ECM), 3D micro-cavities were obtained.

Fabrication of nanometer-sized gold flower microelectrodes for electrochemical biosensing applications

In this work, we present a new method to prepare nanometer-sized gold flower microelectrodes. The carbon fiber electrode was etched with flame to nanometer size in diameter. Then, the surface of carbon fiber was encapsulated by electrophoretic paint. After being heated and baked, the prepared carbon fiber electrode was deposited by gold. The size of prepared gold flower microelectrode was about 100 μm and the dimensions of thorns of the electrode were in nanometers. Thus prepared electrode exhibited excellent performance and the surface of the electrode can be immobilized with specific bioprobes. By combining it with aptamers, we developed an electrochemical biosensor for the detection of cocaine. This sensor was rapid, label-free, selective and sensitive. This electrode is expected to be useful for the detection of molecules in single cells and other microenvironment.

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called “concentric” ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K+]o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na+]o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue.

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called “concentric” ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K+]o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na+]o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.

A simple approach for the fabrication of 3D microelectrodes for impedimetric sensing

In this paper, we present a very simple method to fabricate three-dimensional (3D) microelectrodes integrated with microfluidic devices. We form the electrodes by etching a microwire placed across a microchannel. For precise control of the electrode spacing, we employ a hydrodynamic focusing microfluidic device and control the width of the etching solution stream. The focused widths of the etchant solution and the etching time determine the gap formed between the electrodes. Using the same microfluidic device, we can fabricate integrated 3D electrodes with different electrode gaps. We have demonstrated the functionality of these electrodes using an impedimetric particle counting setup. Using 3D microelectrodes with a diameter of 25 μm, we have detected 6 μm-diameter polystyrene beads in a buffer solution as well as erythrocytes in a PBS solution. We study the effect of electrode spacing on the signal-to-noise ratio of the impedance signal and we demonstrate that the smaller the electrode spacing the higher the signal obtained from a single microparticle. The sample stream is introduced to the system using the same hydrodynamic focusing device, which ensures the alignment of the sample in between the electrodes. Utilising a 3D hydrodynamic focusing approach, we force all the particles to go through the sensing region of the electrodes. This fabrication scheme not only provides a very low-cost and easy method for rapid prototyping, but which can also be used for applications requiring 3D electric field focused through a narrow section of the microchannel.