Planar Microelectrode Research Articles

A Simplified Fabrication Method of Dielectrophoresis Chip Using Au Thin-Film and Box Cutter

We propose fabrication method of a planar quadrupole microelectrode for dielectrophoresis (DEP), which is fabricated by Au thin-film, ion coater and box cutter. This method is more cost effective and simpler than previous existing methods. We conducted two experiments for confirming usefulness of the Au DEP chip. Those are separation of yeast cells and trap force of DEP. To separate yeast cells, we used viable and non-viable cells. DEP force arises when an inhomogeneous AC electric field and sine wave frequency were applied to microelectrode. The Au DEP chip is able to distinguish between viable and non-viable cells and separate them by frequency dependence and the flow with Syringe pump. The chip can obtain viable cells which were trapped without contact to the microelectrode. The viable cells can use for fusion or cell culture. Furthermore, we carried out another experiment to investigate the trap force. The trap force of Negative-DEP becomes gradually weak when the frequency increases with 0.1, 0.5 and 1MHz. We were able to confirm relation between trap force and frequency by the Au DEP chip. The trap force has frequency dependence. Through the two experiments, we have established usefulness of the Au DEP chip.

Dopamine detection using a patch-clamp system on a planar microeletrode array electrodeposited by polypyrrole/graphene nanocomposites

To achieve a dopamine (DA) response with high sensitivity and high signal-to-noise ratio (S/N) with a patch-clamp system, polypyrrole/graphene (PPy/GR) nanocomposites were steadily electrodeposited by an electrochemical method on a planar microelectrode array (pMEA) fabricated by a standard micromachining process. The electrodeposition process was carried out by chronopotentimetry measurement scanning from 0.1 to 0.8 C/cm2 at the current of 2 mA; 0.5 C/cm2 was found to be optimal. The pMEA modified by PPy/GR at the 0.5 C/cm2 exhibits remarkable properties; for instance, the standard deviation (SD) decreases from 8.4614×10−11 to 5.62×10−11 A, reduced by 33.52%, and the sensitivity increases from 2566.88 to 76114.65 μAmMcm−2, 29.65 times higher than the bare Pt (platinum). A good linear relationship between the current and DA concentration in the range of 0.30 to 61.71 μm was obtained, with a correlation coefficient of 0.997. The sensor is meaningful for neuroscience research and the treatment of neurological diseases.

Optical and Electrical Analysis of Suspended Lipid Bilayer Microarrays Formed by Mechanical Liquid Spreading on Horizontal Planar Microelectrode Cavity Arrays

Over the recent years, we have developed a chip-based platform containing a 4x4-array of Ag/AgCl-electrodes in microcavities (6-50μm diam., depth 8-20μm) structured in SU8 (Microelectrode-Cavity-Array, MECA) and demonstrated its application in parallel single molecule detection using biological nanopores in bilayers formed by manual painting (Muller-Rudin procedure). Exploring ways for automation, we found that by spreading lipid/solvent mixtures using a remotely actuated effector highly satisfactory results could be obtained. Here, we use electrical (voltage-clamp) and optical (fluorescence-microscopy) methods to study the formation and morphology of the resulting microbilayers. Despite the difference in geometry between standard “through-hole” apertures and “blind-hole” cavities, the resulting bilayers show classical morphology, i.e. including a lipid-solvent annulus that appears continuous with the lipid-solvent mixture wetting the SU8-surface (Fig.1). It is likely, that these microbilayers are also formed by the thinning process described for standard apertures. This thinning process is, however, greatly accelerated: following automated bilayer formation in the presence of the pore-forming peptide gramicidin, channel events, signaling a bimolecular state of the lipid membrane, could be observed as early as 1050ms after the initial resistance increase (Fig.1).View Large Image | View Hi-Res Image | Download PowerPoint Slide

Dielectrophoresis with 3D microelectrodes fabricated by surface tension assisted lithography

This paper demonstrates the utilization of 3D semispherical shaped microelectrodes for dielectrophoretic manipulation of yeast cells. The semispherical microelectrodes are capable of producing strong electric field gradients, and in turn dielectrophoretic forces across a large area of channel cross-section. The semispherical shape of microelectrodes avoids the formation of undesired sharp electric fields along the structure and also minimizes the disturbance of the streamlines of nearby passing fluid. The advantage of semispherical microelectrodes over the planar microelectrodes is demonstrated in a series of numerical simulations and proof-of-concept experiments aimed toward immobilization of viable yeast cells.

Planar patterned stretchable electrode arrays based on flexible printed circuits

For stretchable electronics to achieve broad industrial application, they must be reliable to manufacture and must perform robustly while undergoing large deformations. We present a new strategy for creating planar stretchable electronics and demonstrate one such device, a stretchable microelectrode array based on flex circuit technology. Stretchability is achieved through novel, rationally designed perforations that provide islands of low strain and continuous low-strain pathways for conductive traces. This approach enables the device to maintain constant electrical properties and planarity while undergoing applied strains up to 15%. Materials selection is not limited to polyimide composite devices and can potentially be implemented with either soft or hard substrates and can incorporate standard metals or new nano-engineered conductors. By using standard flex circuit technology, our planar microelectrode device achieved constant resistances for strains up to 20% with less than a 4% resistance offset over 120 000 cycles at 10% strain.

Preparation and characterization of manganese oxide microelectrodes for microelectromechanical system supercapacitor

The capacity of charge storage for supercapacitor depends on the size of the electrode surface area and the active material on the electrodes. In this article, we fabricate the three-dimensional microelectrodes with SU-8 photoresist based on the microelectromechanical system technology to increase the electrode surface area and to carry more active materials on the electrodes. The three-dimensional microelectrode was directly prepared by the method of anodic electrodeposition. Its surface and composition were characterized by scanning electron microscopy and energy dispersive spectroscopy. Moreover, cyclic voltammetry and galvanostatic charge–discharge current are also used to test the electrochemical characteristics of the manganese oxide electrodes. When the discharge density is 0.5 mA cm−2, the areal capacitance for the fabricated three-dimensional microelectrodes with microstructure and the two-dimensional planar microelectrodes without microstructure is 3.68 mF cm−2 and 1.0 mF cm−2, respectively. The experimental results show that the three-dimensional microelectrode structure prepared with microelectromechanical system technology can effectively increase the electrode surface area and carry more electroactive materials, thereby enhancing the charge storage capacity of the electrodes.

Optimization of planar interdigitated microelectrode array for biofluid transport by AC electrothermal effect

Point-of-care (POC) diagnostics is one of the most important applications for microfluidic research. However, the development of microfluidic POC devices needs to overcome great obstacles to reach market. One challenge is to find a chip-scale pumping strategy that is of low cost, small size, and light weight. Because of their simple implementation, electrokinetic techniques have been extensively investigated as a promising candidate for realizing disposable pumps, with the majority of research effort focusing on direct current and alternating current (AC) electroosmosis. As POC applications often need to handle conductive biofluids with medium to high salt content, AC electrothermal (ACET) effect has been investigated recently for pumping of biofluids, albeit with less than desirable pumping performance. In order to achieve effective on-chip ACET micropumps, this paper presents one of the first efforts in optimizing ACET micropump design utilizing planar interdigitated electrodes. The effects of electrode dimensions on pumping rate were numerically studied using COMSOL Multiphysics and MATLAB, and an optimal ratio of electrode geometry was found for various pumping scenarios. The optimal geometry ratio was tested to be valid over a wide range of electrode characteristic lengths, AC signals, and fluid ionic strengths. Experimental validation of the simulation results was also conducted, and higher flow velocities over prior reports were consistently demonstrated by optimized electrode arrays.

Microarray dot electrodes utilizing dielectrophoresis for cell characterization.

During the last three decades; dielectrophoresis (DEP) has become a vital tool for cell manipulation and characterization due to its non-invasiveness. It is very useful in the trend towards point-of-care systems. Currently, most efforts are focused on using DEP in biomedical applications, such as the spatial manipulation of cells, the selective separation or enrichment of target cells, high-throughput molecular screening, biosensors and immunoassays. A significant amount of research on DEP has produced a wide range of microelectrode configurations. In this paper; we describe the microarray dot electrode, a promising electrode geometry to characterize and manipulate cells via DEP. The advantages offered by this type of microelectrode are also reviewed. The protocol for fabricating planar microelectrodes using photolithography is documented to demonstrate the fast and cost-effective fabrication process. Additionally; different state-of-the-art Lab-on-a-Chip (LOC) devices that have been proposed for DEP applications in the literature are reviewed. We also present our recently designed LOC device, which uses an improved microarray dot electrode configuration to address the challenges facing other devices. This type of LOC system has the capability to boost the implementation of DEP technology in practical settings such as clinical cell sorting, infection diagnosis, and enrichment of particle populations for drug development.

On-chip optical stimulation and electrical recording from cells

We present an optoelectrical device capable of in vitro optical stimulation and electrophysiological recording. The device consists of an array of micropixellated InGaN light-emitting diodes coupled to a custom-made ultrathin planar microelectrode array. Cells can be cultured directly on the chip for short- and long-term electrophysiological experiments. To show the functionality of the device, we transfected a cardiomyocyte-like cell line (HL-1) with a light-sensitive protein channelrhodopsin. We monitored action potentials of individual, spontaneously beating, HL-1 cells growing on the chip by extracellular electrical recordings. On-chip optical stimulation was demonstrated by triggering network activity in a confluent HL-1 cell culture and visualized by calcium imaging. We see the potential of our system for electrophysiological experiments with optogenetically modified cells. Optical stimulation can be performed directly on the chip without additional optical components or external light sources.

Electrosynthesis of polyaniline–mutilwalled carbon nanotube nanocomposite films in the presence of sodium dodecyl sulfate for glucose biosensing

Polyaniline–mutilwalled carbon nanotube (PANi–MWCNT) nanocomposites were electropolymerized in the presence of sodium dodecyl sulfate (SDS) onto interdigitated platinum-film planar microelectrodes (IDμE). The MWCNTs were first dispersed in SDS solution then mixed with aniline and H2SO4. This mixture was used to electro-synthesize PANi–MWCNT films with potentiostatic method at E = + 0.90 V (versus SCE). The PANi–MWCNT films were characterized by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results show that the PANi–MWCNT films have a high electroactivity, and a porous and branched structure that can increase the specific surface area for biosensing application. In this work the PANi–MWCNT films were applied for covalent immobilization of glucose oxidase (GOx) via glutaraldehyde agent. The GOx/PANi–MWCNT/IDμE was studied using cyclic voltammetric and chronoamperometric techniques. The effect of several interferences, such as ascorbic acid (AA), uric acid (UA), and acetaminophen (AAP) on the glucosensing at +0.6 V (versus SCE) is not significant. The time required to reach 95% of the maximum steady-state current was less than 5 s. A linear range of the calibration curve for the glucose concentration lies between 1 and 12 mM which is a suitable level in the human body.

Comparative analysis of system identification techniques for nonlinear modeling of the neuron-microelectrode junction.

Applications of non-invasive neuroelectronic interfacing in the fields of whole-cell biosensing, biological computation and neural prosthetic devices depend critically on an efficient decoding and processing of information retrieved from a neuron-electrode junction. This necessitates development of mathematical models of the neuron-electrode interface that realistically represent the extracellular signals recorded at the neuroelectronic junction without being computationally expensive. Extracellular signals recorded using planar microelectrode or field effect transistor arrays have, until now, primarily been represented using linear equivalent circuit models that fail to reproduce the correct amplitude and shape of the signals recorded at the neuron-microelectrode interface. In this paper, to explore viable alternatives for a computationally inexpensive and efficient modeling of the neuron-electrode junction, input-output data from the neuron-electrode junction is modeled using a parametric Wiener model and a Nonlinear Auto-Regressive network with eXogenous input trained using a dynamic Neural Network model (NARX-NN model). Results corresponding to a validation dataset from these models are then employed to compare and contrast the computational complexity and efficiency of the aforementioned modeling techniques with the Lee-Schetzen technique of cross-correlation for estimating a nonlinear dynamic model of the neuroelectronic junction.

A planar microelectrode array for simultaneous detection of electrically evoked dopamine release from distinct locations of a single isolated neuron

Neurotransmission is a key process of communication between neurons. Although much is known about this process and the influence it has on the function of the body, little is understood about the dynamics of signalling from structural regions of a single neuron. In this study we have fabricated and characterised a microelectrode array (MEA) which was utilised for simultaneous multi-site recordings of dopamine release from an isolated single neuron. The MEA consisted of gold electrodes that were created in plane with the insulation layer using a chemical mechanical planarization process. The detection limit for dopamine measurements was 11 ± 3 nM and all the gold electrodes performed in a consistent fashion during amperometric recordings of 100 nM dopamine. Fouling of the gold electrode was investigated, where no significant change in the current was observed over 4 hours when monitoring 100 nM dopamine. The MEA was accessed using freshly isolated dopaminergic somas from the pond snail, Lymnaea stagnalis, where electrically evoked dopamine release was clearly observed. Measurements were conducted at four structural locations of a single isolated neuron, where electrically evoked dopamine release was observed from the cell body, axonal regions and the terminal. Over time, the release of dopamine varied over the structural regions of the neuron. Such information can provide an insight into the signalling mechanism of neurons and how they potentially form synaptic connections.

A nanoporous alumina microelectrode array for functional cell–chip coupling

The design of electrode interfaces has a strong impact on cell-based bioelectronic applications. We present a new type of microelectrode array chip featuring a nanoporous alumina interface. The chip is fabricated in a combination of top-down and bottom-up processes using state-of-the-art clean room technology and self-assembled generation of nanopores by aluminum anodization. The electrode characteristics are investigated in phosphate buffered saline as well as under cell culture conditions. We show that the modified microelectrodes exhibit decreased impedance compared to planar microelectrodes, which is caused by a nanostructuring effect of the underlying gold during anodization. The stability and biocompatibility of the device are demonstrated by measuring action potentials from cardiomyocyte-like cells growing on top of the chip. Cross sections of the cell–surface interface reveal that the cell membrane seals the nanoporous alumina layer without bending into the sub-50 nm apertures. The nanoporous microelectrode array device may be used as a platform for combining extracellular recording of cell activity with stimulating topographical cues.

Effect of Cell Position on Impedance Measurement in Microfluidic Channel with Planar Microelectrodes and a Three-Pillar Structure

Impedance analysis of single cells offers the possibility of obtaining accurate, reliable, and in-depth information about their pathological condition. In this work, we present the physical capture of a single cell using a microfluidic device with a three-pillar microstructure, impedance measurement using a set of planar microelectrodes, and the derivation of an electrical model that fits the experimental results. The relationship between impedance characteristics and the location of a single HeLa cell (human cervical epithelioid carcinoma) is investigated by impedance spectroscopy. When a single cell fell toward the electrodes after it has been trapped by the three-pillar microstructure, the impedance and the phase change are measured in an operating frequency range of 1 to 100 kHz. The equivalent circuit model is established and two elements that depend on cell location are used to investigate the impedance change of a single HeLa cell.

Effect of Cell Position on Impedance Measurement in Microfluidic Channel with Planar Microelectrodes and a Three-Pillar Structure

Impedance analysis of single cells offers the possibility of obtaining accurate, reliable, and in-depth information about their pathological condition. In this work, we present the physical capture of a single cell using a microfluidic device with a three-pillar microstructure, impedance measurement using a set of planar microelectrodes, and the derivation of an electrical model that fits the experimental results. The relationship between impedance characteristics and the location of a single HeLa cell (human cervical epithelioid carcinoma) is investigated by impedance spectroscopy. When a single cell fell toward the electrodes after it has been trapped by the three-pillar microstructure, the impedance and the phase change are measured in an operating frequency range of 1 to 100 kHz. The equivalent circuit model is established and two elements that depend on cell location are used to investigate the impedance change of a single HeLa cell.

High Aspect-Ratio, Fully Conducting Gold Micropillar Array Electrodes: Silicon Micromachining and Electrochemical Characterization

In this paper we describe the design, fabrication, and characterization of cylindrical gold micropillar array electrodes. Micropillar array electrodes bring about several advantages compared to planar electrodes and microelectrode arrays, as they provide a much larger surface area than the latter devices. Micropillar array electrodes are closely related to porous electrodes, as suggested by the recent literature and as our experimental results show. We fabricated a number of different gold micropillar array structures using standard microfabrication techniques, particularly DRIE plasma etching, thermal oxidations, and gold metallization by dc sputtering. Experimental results were compared with simulations, and very good agreement was found. This served both to validate the diffusion domain approximation for these particular devices and also to deepen our understanding on the modes of mass transport controlling the current response of these devices. We found that planar diffusion dominates the response of ...

Electro-manipulation of biological cells in microdevices

Electric fields are used to manipulate biological cells for diverse applications that include cell counting and sorting, gene delivery, and the creation of novel hybrid cell-types. Although several of these techniques have established applications, others are less studied and are underutilized. Here, we briefly review several electro-manipulations that we achieved using electric fields generated by a common set of inert planar microelectrodes. We supplement our results with selected examples from the literature, and discuss their potential use within miniaturized platforms for single cell science.

An Optimization-Based Study of Equivalent Circuit Models for Representing Recordings at the Neuron–Electrode Interface

Extracellular neuroelectronic interfacing is an emerging field with important applications in the fields of neural prosthetics, biological computation, and biosensors. Traditionally, neuron-electrode interfaces have been modeled as linear point or area contact equivalent circuits but it is now being increasingly realized that such models cannot explain the shapes and magnitudes of the observed extracellular signals. Here, results were compared and contrasted from an unprecedented optimization-based study of the point contact models for an extracellular "on-cell" neuron-patch electrode and a planar neuron-microelectrode interface. Concurrent electrophysiological recordings from a single neuron simultaneously interfaced to three distinct electrodes (intracellular, "on-cell" patch, and planar microelectrode) allowed novel insights into the mechanism of signal transduction at the neuron-electrode interface. After a systematic isolation of the nonlinear neuronal contribution to the extracellular signal, a consistent underestimation of the simulated suprathreshold extracellular signals compared to the experimentally recorded signals was observed. This conclusively demonstrated that the dynamics of the interfacial medium contribute nonlinearly to the process of signal transduction at the neuron-electrode interface. Further, an examination of the optimized model parameters for the experimental extracellular recordings from sub- and suprathreshold stimulations of the neuron-electrode junctions revealed that ionic transport at the "on-cell" neuron-patch electrode is dominated by diffusion whereas at the neuron-microelectrode interface the electric double layer (EDL) effects dominate. Based on this study, the limitations of the equivalent circuit models in their failure to account for the nonlinear EDL and ionic electrodiffusion effects occurring during signal transduction at the neuron-electrode interfaces are discussed.

Reagentless and calibrationless silicate measurement in oceanic waters

Determination of silicate concentration in seawater without addition of liquid reagents was the key prerequisite for developing an autonomous in situ electrochemical silicate sensor (Lacombe et al., 2007) [11]. The present challenge is to address the issue of calibrationless determination. To achieve such an objective, we chose chronoamperometry performed successively on planar microelectrode (ME) and ultramicroelectrode (UME) among the various possibilities. This analytical method allows estimating simultaneously the diffusion coefficient and the concentration of the studied species. Results obtained with ferrocyanide are in excellent agreement with values of the imposed concentration and diffusion coefficient found in the literature. For the silicate reagentless method, successive chronoamperometric measurements have been performed using a pair of gold disk electrodes for both UME and ME. Our calibrationless method was tested with different concentrations of silicate in artificial seawater from 55 to 140×10−6molL−1. The average value obtained for the diffusion coefficient of the silicomolybdic complex is 2.2±0.4×10−6cm2s−1, consistent with diffusion coefficient values of molecules in liquid media. Good results were observed when comparing known concentration of silicate with experimentally derived ones. Further work is underway to explore silicate determination within the lower range of oceanic silicate concentration, down to 0.1×10−6molL−1.

Analytical expression of non steady-state concentration for the CE mechanism at a planar electrode

The analytical solutions of the non-steady-state concentrations of species at a planar microelectrode are discussed. The analytical expression of the kinetics of CE mechanism under first or pseudo-first order conditions with equal diffusion coefficients at planar electrode under non-steady-state conditions are obtained by using Homotopy perturbation method. These simple new approximate expressions are valid for all values of time and possible values of rate constants. Analytical equations are given to describe the current when the homogeneous equilibrium position lies heavily in favour of the electroinactive species. Working surfaces are presented for the variation of limiting current with a homogeneous kinetic parameter and equilibrium constant. In this work we employ the Homotopy perturbation method to solve the boundary value problem. Furthermore, in this work the numerical simulation of the problem is also reported using Scilab program. The analytical results are found to be in excellent agreement with the numerical results.