Flexible Polyimide Microelectrodes Array for Transcorneal Electrical Stimulation

The relationship between the parameters of Transcorneal Electrical Stimulation (TES) and its neuro-protective effect of TES on axotomised Retinal Ganglion Cells (RGCs) is still unclear. This work discusses the design strategy of a new non conventional TES stimulator, the micro fabrication processes and characterization of an array of MEMS microelectrodes over a flexible polymer layer substrate to stimulate the human cornea. The micro-array of electrodes, over a flexible smooth biocompatible polyimide substrate, fine tunes the curvature of the cornea. This tool can help researchers to define the optimal electric stimulation parameters required in TES.

The Measurement of Membrane Potential and NO3 Activity in Root Cells Using Ion-Selective Microelectrodes

Remobilisation of nitrate in plants, especially in vacuole of plant, is mostly related to the qua- lity of agricultural products and the high nitrogen use efficiency in plants. Ion-selective microelectrodes offer a non-destructive and non-interruptive method to measure NO 3 gradients and electric potential differences across both the plasma membrane and tonoplast. Thus, a double-barrelled microelectrode backfilled with a membrane sensor for NO 3 embedded in poly vinyl chloride (PVC) can record the NO 3 activity in cytoplasm and vacuole of a cell. This paper presented how to make this kind of microelectrode and how to do the intracellular measurements on intact plants. Our result showed that nitrate activity was about 2.7 mmol L 1 in cytoplasm while 70 mmol L 1 in vacuole, which implicated that vacuole was a pool of nitrate in plants.

A NEW APPROACH TO THE EQUATIONS FOR THE STEADY STATE CURRENTS AT MICROELECTRODES:EC'PROCESSES(SECOND ORDER REACTION)

With a new approach,the general current expressions of two typical second order catalytic reactions at microelectrodes are obtained.This allows the study of fast chemical reactions and systems where the reactants are present in similar concentrations.

NUCLEATION BEHAVIOURS OF SILVER ON GLASSY CARBON MICROELECTRODES

The initial stage of silver deposition has been investigated using the microelectrode technique A disc shaped nucleus can be obtained on glassy carbon microelectrodes and the instanta. neous nucleation model applies for the process

INVESTIGATION ON MICROELECTRODES Ⅻ THE DETERMINATION OF THE INVERSE CURRENT IN THE PROCESSES OF STEADY-STATE OR QUASI-STEADY-STATE

A simple method for determining the inverse current of cyclic voltammetry in the processes of steady-state or quasi-steady-state was presented. The experimental result verified the theoretical relation or inverse and forward current at microelectrode. Their ratio is proportional to the square root of scan rate.

Powder Microelectrodes Applied to NO2- Detection

TheelectrochemicalbehaviorsandthedetectionofNO2-haveattractedincreasingattentionrecentlybecauseoftheimportantrolesplayedbyNO2-inenvironmentandlifeprocesses.Thus,advancedtechniquesforthedetermination,especiallyon-sitedetermination,ofthenitriteinfoods...

Research on Electric Impedance Spectroscopy of Living Cell Suspensions by a Chip with Microelectrodes

A microfabricated electrical impedance spectroscopy (EIS) chip with microelectrodes was developed.The substrate and the electrodes of the chip were made of glass and gold,respectively.The experimental results demonstrated that the EIS-chip could distinguish different solutions (physiological saline,culture medium,living cell suspension etc.) by scanning from 10Hz to 45kHz.A 6-element circuit model was used for fitting the real part and the imaginary part admittance curves of the living cell suspension.An actual circuit was also built and tested to verify the 6-element circuit model proposed.The micro-EIS chip has several advantages including the use of small sample volumes,high resolution and ease of operation.It shows good application prospects in the areas of cellular electrophysioiogy,drug screening and bio-sensors etc.

Construction of DNA-based logic gates on nanostructured microelectrodes

Electrochemical logical operations utilizing biological molecules(protein or DNA), which can be used in disease diagnostics and bio-computing, have attracted great research interest. However, the existing logic operations, being realized on macroscopic electrode, are not suitable for implantable logic devices. Here, we demonstrate DNA-based logic gates with electrochemical signal as output combined with gold flower microelectrodes. The designed logic gates are of fast response, enzyme-free, and micrometer scale. They perform well in either pure solution or complex matrices, such as fetal bovine serum,suggesting great potential for in vivo applications.

Electrochemical Fabrication and Electrocatalytic Properties of Nanostructured Mesoporous Platinum Microelectrodes

Electrodeposition from a lyotropic liquid crystal template medium was used to produce nanostructured platinum microelectrodes with high specific surface area and high mass transport efficiency. Compared to polished and conventional platinized microelectrodes, well-ordered nanostructured platinum microelectrodes exhibited enhanced electrocatalytic properties for oxygen and ascorbic acid, whilst well-ordered nanostructured platinum microelectrodes offered improved electrocatalytic properties for oxygen reduction compared to disordered nanostructured platinum microelectrodes.

Amperometric Detection of Histamine and Amino Acid Neurotransmitters in Capillary Electrophoresis with Copper Microelectrodes

Copper microelectrodes were used in microvoltammetry to detect histamine and several amino acid neurotransmitters. High sensitivity was obtained through the use of copper microelectrodes, and detection limits of 50 nmol/L and 90 nmol/L were obtained for histamine and histidine, respectively. Furthermore, histamine and several amino acids neurotransmitters were firstly separated and detected by capillary electrophoresis with amperometric detection on copper microelectrodes. Mass limits of 490 amol and 440 amol were achieved for histamine and histidine, respectively, by using this mothod.

Determination of Epinephrine Using Poly(Neutral Red)Modified Carbon Fibre Microelectrodes by Anodic Stripping Voltammetry

Poly(neutral red) film modified carbon fibre microelectrodes offer substantial improvement in voltammetric sensitivity and selectivity towards epinephrine (EP). The poly(neutral red) film was electropolymerized by cycling the potential between -0.8 V and +0.8 V. The anodic stripping voltammetric response for EP was found to be dependent on accumulation time and potential. By using a poly(neutral red) film modified carbon fibre microelectrode with a 1 min preconcentration at -1.2 V in biological phosphate buffer solution (pH=7.4), a good linear relationship between the anodic stripping peak currents and EP concentrations was obtained in the range of 2.0×10 -7 ￣ 2.0×10 -5 mol/L. The detection limit was up to 9.0 ×10 -8 mol/L. Moreover, 400 times higher concentrations of vitamin C did not interfere with the measurement of EP. This method was used for determining EP concentrations in epinephrine hydrochloride injection solution with satisfactory results.

Implantable intracortical microelectrodes: reviewing the present with a focus on the future

Implantable intracortical microelectrodes can record a neuron’s rapidly changing action potentials(spikes).In vivo neural activity recording methods often have either high temporal or spatial resolution,but not both.There is an increasing need to record more neurons over a longer duration in vivo.However,there remain many challenges to overcome before achieving long-term,stable,high-quality recordings and realizing comprehensive,accurate brain activity analysis.Based on the vision of an idealized implantable microelectrode device,the performance requirements for microelectrodes are divided into four aspects,including recording quality,recording stability,recording throughput,and multifunctionality,which are presented in order of importance.The challenges and current possible solutions for implantable microelectrodes are given from the perspective of each aspect.The current developments in microelectrode technology are analyzed and summarized.

Extracellular matrix-based intracortical microelectrodes:Toward a microfabricated neural interface based on natural materials

Extracellular matrix(ECM)-based implantable neural electrodes(NEs)were achieved using a microfabrication strategy on naturalsubstrate-based organic materials.The ECM-based design minimized the introduction of non-natural products into the brain.Further,it rendered the implants sufficiently rigid for penetration into the target brain region and allowed them subsequently to soften to match the elastic modulus of brain tissue upon exposure to physiological conditions,thereby reducing inflammatory strain fields in the tissue.Preliminary studies suggested that ECM-NEs produce a reduced inflammatory response compared with inorganic rigid and flexible approaches.In vivo intracortical recordings from the rat motor cortex illustrate one mode of use for these ECM-NEs.

Three-dimensional fuzzy graphene ultra-microelectrodes for subcellular electrical recordings

Microelectrode arrays(MEAs)have enabled investigation of cellular networks at sub-millisecond temporal resolution.However,current MEAs are limited by the large electrode footprint since reducing the electrode’s geometric area to sub-cellular dimensions leads to a significant increase in impedance thus affecting its recording capabilities.We report a breakthrough ultra-microelectrodes platform by leveraging the outstanding surface-to-volume ratio of nanowire-templated out-of-plane synthesized three-dimensional fuzzy graphene(NT-3DFG).The enormous surface area of NT-3DFG leads to 140-fold reduction in electrode impedance compared to bare Au microelectrodes,thus enabling scaling down the geometric size by 625-fold to ca.2µm×2µm.The out-of-plane morphology of NT-3DFG leads to a tight seal with the cell membrane thus enabling recording of electrical signals with high signal-to-noise ratio(SNR)of>6.This work highlights the possibility to push the limits of the conventional MEA technology to enable electrophysiological investigation at sub-cellular level without the need of any surface coatings.This presented approach would greatly impact our basic understanding of signal transduction within a single cell as well as complex cellular assemblies.

Indirect Electroanalysis of 3-Methyl-4-Nitrophenol in Water Using Carbon Fiber Microelectrode Modified with Nickel Tetrasulfonated Phthalocyanine Complex

Electrochemical detection of 3-methyl-4-nitrophenol (MNP) in direct phenol oxidation occurs at high potentials and generally leads to progressive passivation of the electrochemical sensor. This study describes the use of a carbon fiber microelectrode modified with a tetrasulfonated nickel phthalocyanine complex for the detection of MNP at a lower potential than that of direct phenol oxidation. The MNP voltammogram showed the presence of an anodic peak at -0.11 V vs SCE, corresponding to the oxidation of the hydroxylamine group generated after the reduction of the nitro group. The effect of buffer pH on the peak current and SWV parameters such as frequency, scan increment, and pulse amplitude were studied and optimized to have better electrochemical response of the proposed sensor. With these optimal parameters, the calibration curve shows that the peak current varied linearly as a function of MNP concentration, leading to a limit of detection (LoD) of 1.1 μg/L. These results show an appreciable sensitivity of the sensor for detecting the MNP at relatively low potentials, making it possible to avoid passivation phenomena.

A theoretical analysis and its application of the second order EC' reactions at microelectrodes under steady-state conditions

With a new approach,the general current expressions of two typical second order catalytic reactions are obtained for disk,hemispherical and spherical microelectrodes under steady-state conditions.This approach is based on the concept of reaction layer.For the second order EC' reactions,we also discussed how it is possible to observe pseudo-first order or second order behavior.This consideration allows the study of the fast chemical reactions and systems where the bulk concentrations of the reactants are nearly equal.Regeneration of Fe^(3+)(EDTA) with H_2O_2 was selected as an example of a rapid catalytic reaction.

3D Printing Engineered Multi-porous Cu Microelectrodes with In Situ Electro-Oxidation Growth of CuO Nanosheets for Long Cycle,High Capacity and Large Rate Supercapacitors

Developing excellent pseudocapacitive electrodes with long cycle,high areal capacity and large rate has been challenged.3 D printing is an additive manufacture technique that has been explored to construct microelectrodes of arbitrary geometries for high-energy–density supercapacitors.In comparison with conventional electrodes with uncontrollable geometries and architectures,3 D-printed electrodes possess unique advantage in geometrical shape,mechanical properties,surface area,especially in ion transport and charge transfer.Thus,a desirable 3 D electrode with ordered porous structures can be elaborately designed by 3 D printing technology for improving electrochemical capacitance and rate capability.In this work,a designed,monolithic and ordered multi-porous 3 D Cu conductive skeleton was manufactured through 3 D direct ink writing technique and coated with Cu O nanosheet arrays by an in situ electro-oxidation treatment.Benefiting from the highly ordered multiporous nature,the 3 D-structured skeleton can eff ectively enlarge the surface area,enhance the penetration of electrolyte and facilitate fast electron and ion transport.As a result,the 3 D-printed Cu deposited with electro-oxidation-generated CuO(3 DP Cu@Cu O)electrodes demonstrates an ultrahigh areal capacitance of 1.690 F cm^(-2)(38.79 F cm^(-3))at a large current density of 30 m A cm^(-2)(688.59 m A cm^(-3)),excellent lifespan of 88.20%capacitance retention after 10,000 cycles at 30 m A cm^(-2) and superior rate capability(94.31%retention,2-30 m A cm^(-2)).This design concept of 3 D printing multi-porous current collector with hierarchical active materials provides a novel way to build high-performance 3 D microelectrodes.

Microfluidics embedded with microelectrodes for electrostimulation of neural stem cells proliferation

The regeneration of the injured nerve and recovery of its function have brought attention in the medical field. Electrical stimulation(ES) can enhance the cellular biological behavior and has been widely studied in the treatment of neurological diseases. Microfluidic technology can provide a cell culture platform with the well-controlled environment. Here a novel microfluidic/microelectrode composite microdevice was developed by embedding the microelectrodes to the microfluidic platform, in which microfluidics provided a controlled cell culture platform, and ES promoted the NSCs proliferation. We performed ES on rat neural stem cells(NSCs) to observe the effect on their growth, differentiation, proliferation, and preliminary explored the ES influence on cells in vitro. The results of immunofluorescence showed that ES had no significant effect on the NSCs specific expression, and the NSCs specific expression reached 98.9%± 0.4% after three days of ES. In addition, ES significantly promoted cell growth and the cell proliferation rate reached 49.41%. To conclude, the microfluidic/microelectrode composite microdevice can play a positive role in the nerve injury repair and fundamental research of neurological diseases.

Physiological Responses of Two Wheat Cultivars to Nitrogen Starvation

Plants need to be efficient in nutrient management, especially when they face the temporal nutrient defficiencies. Understanding how crops respond to nitrogen （N） starvation would help in the selection of crop cultivars more tolerant to N deficiency. In the present work, the physiological responses of two wheat cultivars, Yannong 19 （YN） and Qinmai 11 （QM）, to N starvation conditions were investigated. The two cultivars differed in biomass and N rearrangement between shoots and roots during N starvation. QM allocated more N to roots and exhibited higher root/shoot biomass ratio than YN. However, tissue measurement indicated that both cultivars had similar nitrate content in leaves and roots and similar remobilization rate in roots. Microelectrode measurement showed that vacuolar nitrate activity （concentration） in roots of QM was lower than that in roots of YN, especially in epidermal cells. Nitrate remobilization rates from root vacuoles of two cultivars were also identical. Moreover, vacuolar nitrate remobilization rate was proportional to vacuolar nitrate activity. During N starvation, nitrate reductase activity （NRA） was decreased but there were no significant differences between the two cultivars. Nitrate efflux from roots reduced after external N removal and QM seemed to have higher nitrate efflux rate.

Exocytosis determination of SH-SY5Y single cell stimulated by diff erent stimulants on indium tin oxide (ITO) micro-pore electrode

The human neuroblastoma SH-SY5Y cell line has been used as a model to study mechanisms of neurotransmitter release.In order to study the mechanism of SH-SY5Y single cell exocytosis stimulated by different stimulants,including high K+,3-(1-nitroso-2-pyrrolidinyl)pyridine and nicotine,a type of indium tin oxide(ITO)micro-pore electrode was used to obtain the corresponding amperometric response time.When the cell is stimulated by 0.1 M K+,almost immediate exocytosis could be detected,due to the rapid depolarization of cell membrane.However,the stimulations with 1 mM nicotine and 3-(1-nitroso-2-pyrrolidinyl)pyridine result in a short delay between stimulation and exocytosis,which can be correlated with the time needed for binding of the stimulant to the nicotinic acetylcholine(ACh)receptor and the induction of post-binding phenomena.Thus,the response time of SH-SY5Y single cell exocytosis is significantly affected by the exocytosis mechanisms.