Cavity Electrode Research Articles

HERG Ion Channel Activity Measured in Planar Lipid Bilayer Arrays: Reconstitution from Eukaryotic Cell-Free Expression System and Cellular Membrane Preparations

Ion channels are important pharmacological targets. Therefore there is an urgent need for new technologies for high throughput ion channel activity monitoring and pharmacology screening capable to substitute currently used labor-intensive and expensive cell-based electrophysiological assays. Ion channels reconstituted into artificial membrane arrays may serve as such test system offering a substantial simplification as well as great flexibility in controlling the ion channel environment and experimental conditions.Human ether-a-go-go-related gene (hERG), a voltage dependent potassium channel is a major target of pharmacology safety screening due to its critical importance in heart function. Here we report on parallel high-resolution electrophysiological recordings from different hERG-containing preparations reconstituted into bilayer lipid membranes on the micro electrode cavity array (MECA) chip.Two different sources of hERG channels have been investigated: (1) Membrane preparations from a hERG-expressing HEK293 cell line, and (2) Vesicles collected after cell-free expression of the hERG channels with their co-translational integration into microsomes or liposomes. The hERG-containing vesicles were fused with lipid bilayers preformed on the MECA chip. For both preparations fluctuating currents of different amplitudes have been recorded following the fusion. Single channel and channel ensemble currents depending on the vesicle preparation have been characterized. The recorded currents were shown to be partially inhibited by the hERG specific blockers E4031 and astemizole.High channel expression level as well as optimized vesicles preparation and fusion conditions were shown to be crucial for the reproducible channel recordings in the artificial membrane system. Addition of charged lipids (POPG/DOTAP) to the liposomes and acceptor membranes was found to facilitate vesicle fusion and improve the measurements success rate. The presented technology has a potential for a high throughput ion channels pharmacology screening in general.

Modulation of Thermo-TRP Channels by Temperature in Planar Lipid Bilayers

Thermal Transient receptor potential (TRP) channels belong to the large family of TRP channels. They are an important class of receptors found widely distributed throughout the mammalian central and peripheral nervous systems. They have been shown to be directly activated by heat or cold in physiologically relevant temperature ranges, but are also activated by mechano-stimulation and various ligands. Understanding the mechanisms of temperature activation could lead to the discovery of novel compounds with differing effects on ligand activation and temperature activation for the treatment of pain and other disease states, with fewer side effects.We have employed parallel planar lipid bilayer instrumentation (Orbit, Nanion) to study different reconstituted thermo-TRP channels, particularly the purified human TRP-A1, -V1, -V3 and -M8 channels. Planar lipid bilayers can be formed by painting over Micro Electrode Cavity Array (MECA) chips, a 2 by 2 array of circular micro-cavities in a highly inert polymer. The reconstitution of the proteins is achieved by adding the purified proteins directly to the bilayers.In this study, we demonstrate the activation of the different TRP channels by cold and heat in a fully controlled environment using artificial membranes and the use of a peltier element to actively cool and heat the system to the desired temperature (±1°C). Furthermore, we compared our Q10 data from purified proteins to TRP channels expressed in HEK cells (Millipore, Chantest) using an automated patch clamp platform (Patchliner, Nanion) with temperature control.Our results support the hypothesis that temperature sensitivity is located within the channels and does not require any second messengers, including calcium or accessory proteins.

Fabrication of Capacitive Micromachined Ultrasonic Transducer Arrays With Isolation Trenches Using Anodic Wafer Bonding

This paper presents a novel process for the fabrication of capacitive micromachined ultrasonic transducer (CMUT) arrays with isolation trenches using anodic bonding technique. The developed fabrication process is easy, stiction-free, repeatable, reliable, requires low-temperature (<;400°C), and gives high yield. It is a four-mask process. The process is best suited for air-coupled CMUT devices, and can also be used for vacuum-sealed devices. The CMUT device is designed and fabricated successfully using the developed process, which requires silicon-on-insulator (SOI) wafer for membrane and cavity formation, and Pyrex glass wafer for cavity and bottom electrode formation. The process is used for single-cell as well as for development of 1 × 5, 5 × 5, and 10 × 10 CMUT arrays. CMUT cells were designed using MEMSCAD tool CoventorWare. The fabricated devices have been characterized using nanovibration analyzer, and the resonance frequency is found to be ~1.5 MHz.

Nanostructured cavity devices for extracellular stimulation of HL-1 cells.

Microelectrode arrays (MEAs) are state-of-the-art devices for extracellular recording and stimulation on biological tissue. Furthermore, they are a relevant tool for the development of biomedical applications like retina, cochlear and motor prostheses, cardiac pacemakers and drug screening. Hence, research on functional cell-sensor interfaces, as well as the development of new surface structures and modifications for improved electrode characteristics, is a vivid and well established field. However, combining single-cell resolution with sufficient signal coupling remains challenging due to poor cell-electrode sealing. Furthermore, electrodes with diameters below 20 µm often suffer from a high electrical impedance affecting the noise during voltage recordings. In this study, we report on a nanocavity sensor array for voltage-controlled stimulation and extracellular action potential recordings on cellular networks. Nanocavity devices combine the advantages of low-impedance electrodes with small cell-chip interfaces, preserving a high spatial resolution for recording and stimulation. A reservoir between opening aperture and electrode is provided, allowing the cell to access the structure for a tight cell-sensor sealing. We present the well-controlled fabrication process and the effect of cavity formation and electrode patterning on the sensor's impedance. Further, we demonstrate reliable voltage-controlled stimulation using nanostructured cavity devices by capturing the pacemaker of an HL-1 cell network.

Investigation of electrochemical reduction of GeO2 to Ge in molten CaCl2-NaCl

Electrochemical reduction of solid GeO2 has been investigated in the mixed CaCl2-NaCl melt at 1023K for developing a more efficient process for preparation of Ge. Cyclic voltammetry and potentiostatic electrolysis were applied to study the GeO2-loaded metallic cavity electrode. In addition, porous GeO2 pellets were reduced by potentiostatic and constant cell voltage electrolysis with a graphite anode, and the electrolysis products were analyzed by powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry, focusing on understanding the reduction mechanism and the impact of electrode potential on the product purity. It was found that the reduction of GeO2 to Ge occurred at a potential of about -0.50V (vs. Ag/Ag+), but generating various calcium germanates simultaneously, whose reduction was a little more difficult and needed a potential more negative than -1.00V. However, if the cathode potential exceeded -1.60V, Ca (or Na) - Ge intermetallic compounds might form. These results gave an appropriate potential range between -1.10 and -1.40V for the production of pure germanium. Rapid electrolysis of GeO2 to pure Ge has been realized at a cell voltage of 2.5V with a current efficiency of about 92%.

Voltammetric behavior of carboxyl hydrogel particles on a cavity electrode surface

A platinum electrode with two-dimensional ordered arrays of hemispherical cavities was fabricated via the inverted crystal template technique. Due to the overlap of the diffusion zones, voltammetric response of ferricyanide at the cavity platinum (CPt) electrode was almost the same as that at a flat platinum (FPt) electrode. Uniformly sized poly(N-isopropylacrylamide-co-acrylic acid) (NIPA/AA) hydrogel particles were synthesized and modified into the cavities of the CPt electrode. Voltammograms of the NIPA/AA-CPt electrode showed a cathodic peak at −0.38V in the negative potential range. The peak was attributed to the reduction of H+ which supplied from the dissociation of carboxyl groups of the absorbed particles. Compared with the peak observed at NIPA/AA-FPt electrode, the peak potential was shifted in the positive direction by 0.19V. The peak current was increased linearly with the loaded amount of the particles, and was controlled by the participation of diffusion, adsorption and dissociation. The electron-transfer rate constant between dissociated H+ and the CPt electrode was estimated to be one order smaller than that between ferricyanide and the FPt electrode.

Parallel Reconstitution of Bacterial Toxins, Porins and Ion Channels into Suspended Lipid Membrane Microarrays for High-Throughput Electrophysiology

High-throughput electrophysiological recordings in artificial membranes have a great potential for pharmaceutical screening and nanopore analytics. In addition to parallelization and automation of lipid bilayers formation, different protein reconstitution protocols are required depending on the concrete application.We report on functional reconstitutions of three classes of pore-forming proteins into suspended lipid bilayers on Micro Electrode Cavity Array (MECA). Three reconstitution strategies have been employed and optimized depending on the protein structure: self-insertion for pore-forming toxins, transfer from detergent micelles for porins and vesicle fusion for ion channels.By optimizing protein concentration and facilitating spontaneous insertion with short voltage pulses just below the electroporation threshold, a controlled insertion of alpha-hemolysin was achieved. Exactly one pore per bilayer was inserted in over 50% of bilayers in the array, which is substantially higher than the 37% predicted by the Poisson distribution.We investigated and optimized insertion of outer membrane porins OmpF, MspA and OccK1 into bilayer arrays via detergent dilution. Best strategy was to use mild nonionic detergents and sequentially dilute protein stock solution to minimize influence of the detergent on the membrane. Protein injection in the immediate vicinity of a bilayer array and thorough mixing of the solution were decisive factors for homogeneous distribution of functional porins.Reconstitution via detergent micelles was found to be problematic for ion channels, but proteovesicle fusion was successful. The tetrameric potassium channel KcsA was expressed in vitro with cotranslational insertion into lipid vesicles or nanodiscs. Transfer from nanodiscs into suspended bilayers was shown to be inefficient. Additionally, the presence of nanodiscs substantially destabilized the membranes. For proteovesicles best fusion rates were achieved upon addition of negatively charged phospholipids followed by extrusion of the recovered proteovesicles through a polycarbonate filter.

Metallurgical alterations in the surface of steel cavities machined by EDM

The electrical discharge machining (EDM) is a process characterized by high thermal demands, which tend to cause metallurgical changes in the surface of the workpiece [1-2]. This work aims to conduct a discussion of metallurgical changes in the surface of cavities obtained by the process of EDM in the machining of steel. Several variables were employed, such as cavity depth, electrode geometry and technological parameters of the process. Thus, the goal was to identify the different metallurgical changes that can occur in the machined surfaces. The evaluation of these changes was made from metallographic analysis, measurements of microhardness and of the depth of the layer affected by process. The results of this work identified several metallurgical changes such as formation of white layer, hardness variation and change of microstructure. The occurrence of microcracks also was observed, especially in severe conditions. The greatest variations in results were caused by the change of technological parameters. However, the variation in cavity depth and the change of the electrode geometry also showed influence on the results.

Novel design of a micro-pulse electron gun

The development of the micro-pulse electron gun (MPG) mainly relies on the mechanism of the evolutionary process for the multipacting effect. On the other hand, mitigating the limitations of multipacting is what we needed. Here, a new kind of cavity shape is proposed to confine multipacting effect within the spatial range of electrodes, which is of interest to avoiding the occurrence of multipacting in the copper cavity. Based on the theoretical analysis of the saturation process, it is found that increasing the number of impacts for electrons until to saturation is important to attain high quality bunches, while at the expense of losing out-of-phase electrons. In this paper, a novel electrode structure is studied in detail using both theoretical analysis and numerical simulations in order to improve the performance of the gun. After optimizing the cavity shape and electrode structure, the beam quality and saturation currents are maximized and the simulation results are presented.

A simple chip free‐flow electrophoresis for monosaccharide sensing via supermolecule interaction of boronic acid functionalized quencher and fluorescent dye

Here, a simple micro free-flow electrophoresis (μFFE) was developed for fluorescence sensing of monosaccharide via supermolecule interaction of synthesized boronic acid functionalized benzyl viologen (ο-BBV) and fluorescent dye. The μFFE contained two open electrode cavities and an ion-exchange membrane was sandwiched between two polymethylmethacrylate plates. The experiments demonstrated the following merits of developed μFFE: (i) up to 90.5% of voltage efficiency due to high conductivity of ion-exchange membrane; (ii) a strong ability against influence of bubble produced in two electrodes due to open design of electrode cavities; and (iii) reusable and washable separation chamber (45 mm × 17 mm × 100 μm, 77 μL) avoiding the discard of μFFE due to blockage of solute precipitation in chamber. Remarkably, the μFFE was first designed for the sensing of monosaccharide via the supermolecule interaction of synthesized ο-BBV, fluorescent dye, and monosaccharide. Under the optimized conditions, the minimum concentration of monosaccharide that could be detected was 1 × 10(-11) M. Finally, the developed device was used for the detection of 0.3 mM glucose spiked in human urine. All of the results demonstrated the feasibility of monosaccharide detection via the μFFE.

Common cavity and custom-made electrodes: Speech perception and audiological performance of children with common cavity implanted with a custom-made MED-EL electrode

ObjectiveFew studies exist on children with common cavity, fewer still on their long-term audiological development after having received a cochlear implant. Our goal was to observe and report the long-term audiological progress of children with common cavity who were implanted with a custom-made electrode. MethodsIn this longitudinal, multi-center study, 19 children were implanted with a MED-EL custom-made electrode via either single slit cochleostomy or double posterior labyrinthotomy. We observed their audiological development with a test battery consisting of Categories of Auditory Performance (CAP), Speech Intelligibility Rating (SIR), and Ling 6-Sounds tests. We tested the children 1 month prior to the surgery; at first fitting; at 1, 3, 6, 12, and 18 months post first-fitting; at 2 years after first-fitting; and, whenever possible, at 3, 4, and 5 years after first-fitting. ResultsChildren with common cavity tend to steadily and significantly improve their audiological skills over time. This development may, however, be highly individual; probably in part due to relatively high levels of additional needs. Parents should be counseled to establish realistic post-implantation expectations. Surgically, contrary to our expectations, we cannot confirm that double posterior labyrinthotomy reduces intracochlear electrode movement or that the MED-EL custom electrode leads to fewer incidences of intra- or post-implantation complications. ConclusionsCochlear implantation is a safe and effective treatment option in children with common cavity. The majority of children with CC derive significant audiological benefit from implantation. Intra- and post-surgical complications, while serious, and be dealt with effectively in most cases.

Template-free electrosynthesis of crystalline germanium nanowires from solid germanium oxide in molten CaCl2–NaCl

Germanium nano-materials are attractive due to their potential application prospects in electronic, information and energy industry. Herein we report a one-step preparation of crystalline germanium nanowires (Ge-NWs) by direct electrochemical reduction of solid GeO2 in molten CaCl2–NaCl at 600°C with a current efficiency of ~86% and an energy consumptions as low as 3.26kWh (kgGe)−1. The cyclic voltammogram of the GeO2-filled cavity electrode shows that the onset electroreduction potential of GeO2 is −1.0V vs. Ag/Ag+, much more positive than the reduction potential of cations in the melt. The as-prepared Ge-NWs are of high aspect ratio, high purity and good crystallinity according to the XRD, EDX, SEM and TEM characterizations. The present approach provides a simple and short process for the production of Ge-NWs from a cost-affordable germanium precursor (GeO2). The potential applications of the obtained Ge for photodetector and infrared optical window have been also investigated by Raman and FT-IR measurements.

Electrochemical cholesterol sensor based on carbon nanotube@molecularly imprinted polymer modified ceramic carbon electrode

A monolithic molecular imprinting sensor based on ceramic carbon electrode (CCE) has been reported. The sensor can be renewed simply by smoothing. It was fabricated by thoroughly mixing multiwalled carbon nanotube@molecularly imprinted polymer (MWCNT@MIP), graphite powder, and silicon alkoxide, and then packing the resulting complex mixture of components firmly into the electrode cavity of a Teflon sleeve. The incorporated MWCNT@MIP in CCEs functioned as a recognition element for cholesterol determination. The MWCNT@MIP-CCEs were tested in the presence or absence of cholesterol by cyclic voltammetry and linear sweep voltammetry. The cholesterol sensor has excellent sensitivity with a linear range of 10–300nM and a detection limit of 1nM (S/N=3). The monolithic molecular imprinting sensor exhibits good stability, high sensitivity, and user-friendly reusability for cholesterol determination. This study shows that CCE is a promising matrix for MIP sensors.

Up-scalable and controllable electrolytic production of photo-responsive nanostructured silicon

The electrochemical reduction of solid silica has been investigated in molten CaCl2 at 900 °C for the one-step, up-scalable, controllable and affordable production of nanostructured silicon with promising photo-responsive properties. Cyclic voltammetry of the metallic cavity electrode loaded with fine silica powder was performed to elaborate the electrochemical reduction mechanism. Potentiostatic electrolysis of porous and dense silica pellets was carried out at different potentials, focusing on the influences of the electrolysis potential and the microstructure of the precursory silica on the product purity and microstructure. The findings suggest a potential range between −0.60 and −0.95 V (vs. Ag/AgCl) for the production of nanostructured silicon with high purity (>99 wt%). According to the elucidated mechanism on the electro-growth of the silicon nanostructures, optimal process parameters for the controllable preparation of high-purity silicon nanoparticles and nanowires were identified. Scaling-up the optimal electrolysis was successful at the gram-scale for the preparation of high-purity silicon nanowires which exhibited promising photo-responsive properties.

Synthesis of large surface area carbon xerogels for electrochemical double layer capacitors

A resorcinol–formaldehyde (R–F) condensation reaction catalyzed by acetic acid (C) is employed to prepare carbon xerogels for electrochemical double layer capacitors. The samples are fabricated with an R:F ratio of 1:2 and R:C ratio of 10:1, followed by solvent exchange, pyrolysis, and carbon dioxide activation. The solvent exchange allows negligible structure contraction upon drying, and after pyrolysis and carbon dioxide treatment, we are able to produce porous carbons with a surface area of 3419 m2 g−1. Image from scanning electron microscope reveals an interconnected foam-like structure and BET confirms the presence of excessive micro- and mesopores. Electrochemical analysis including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are conducted using a titanium cavity electrode so relevant capacitive characteristics and kinetic parameters could be determined. Both CV and CRC results indicate specific capacitances and life time behaviors that are comparable or even better than those of Black Pearl 2000. For example, the specific capacitance is 324.8 F g−1 in 0.5 M H2SO4 aqueous solution at ±1 A g−1 for potential window of 0–1 V. In contrast, sample without carbon dioxide activation displays a similar morphology but its surface area and specific capacitance are reduced considerably to 449 m2 g−1 and 34.7 F g−1, respectively.

Direct electrochemical preparation of CeCo5 alloy from mixed oxides

CeCo5 alloy was prepared from the mixture of cobalt oxide (Co3O4) and cerium oxide (CeO2) powders by electro-deoxidation in molten calcium chloride. The effects of the cell voltage and sintering temperature on the electrolysis process were reported. The electro-deoxidation mechanism was investigated by potentiodynamic polarization using a molybdenum cavity electrode in conjunction with characterization of the products from constant voltage electrolysis under different conditions by XRD and SEM. The electrochemical property of CeCo5 alloy was investigated by cyclic voltammetry measurements. The results show that the electro-deoxidation rate increases with increasing the cell voltage and decreasing the sintering temperature. The pure CeCo5 can be prepared by direct electro-deoxidation of mixed CeO2/Co3O4 pellets sintered at 850 °C when the cell voltage of 3.1 V is applied. The electro-deoxidation proceeds by the simultaneous reduction of Co3O4 to Co and reduction of CeO2 to CeOCl, followed by CeOCl reduction on the pre-formed Co to form CeCo5 alloy which shows a good cycling stability.

Dielectrophoretic Positioning of Cells on Planar Microelectrode Cavity Arrays (MECA) for High Throughput Patch-Clamp Measurements

Electrically tight sealing of cells is important for low-noise and stable patch-clamp recordings. In situations where the application of fluid-mechanical forces is not feasible, positioning of cells on planar electrodes is challenging. It has been reported, however, that vesicles and cells may be positioned and sealed on µm-sized apertures by dielectrophoresis(Schmidt et al. 2000, Angew. Chem. Int. Ed. 39,3137 & EP 1040349B1). We have explored a similar approach for cell positioning on microelectrode cavity arrays(MECA). 6 µm electrode cavities in SU8 photoresist were spin-coated with a hydrophobic coating followed by polylysine physisorption. Cell suspensions(RBL-2H3 & CHO cells) were allowed to sediment on the MECA surface while applying a sequence of alternating voltage pulses of ms duration. Cells were selectively placed over the cavities with approximately 50% success rate. However, only moderate increases in electrode resistance were observed. We conclude that while dielectrophoretic positioning of the cells tested here is in principle feasible with MECAs, polylysine appears to be not an ideal surface coating for seal formation.Figure. (A) Scheme of the measurement set up (B) A single RBL-2 cell placed over the microelectrode cavity by dielectrophoresis.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Evaluation on carbon nanocapsules for supercapacitors using a titanium cavity electrode

We synthesize carbon nanocapsules (CNCs) by a flame combustion method and evaluate their potential as the electrode material for electrochemical double layer capacitor using a titanium cavity electrode (TCE). Identical process is conducted on commercially available carbonaceous materials such as Vulcan XC72R, Black Pearl 2000 (BP2000), multi-walled carbon nanotubes (MWCNTs), and active carbon (AC1100) for comparison purposes. Images from Scanning electron microscope and Transmission electron microscope on the CNCs demonstrate irregular-shaped particles in average size of 10–20 nm with graphene layers on perimeter compassing a hollow core. Electrochemical characterizations including cyclic voltammetry (CV), current reversal chronopotentiometry (CRC), and impedance spectroscopy are carried out in 1N H 2SO 4 to determine the specific capacitance and cycle life time. Among these samples, the BP2000 still delivers the highest specific capacitance in F g −1 but the CNCs demonstrate the largest value in μF cm 2. In addition, the CNCs exhibit impressive life time for 5000 cycles without notable degradation. Consistent results are obtained by CV, CRC, and impedance measurements, validating the TCE as a facile tool to perform reliable electrochemical evaluations.

Cyclic Voltammetry of ZrO2 Powder in the Metallic Cavity Electrode in Molten CaCl2

The electrochemical reduction of the insulative powder in molten was investigated using the metallic cavity electrode (MCE) in molten at . Cyclic voltammograms (CVs) revealed two consecutive reduction peaks corresponding to (i) to and (ii) to Zr. The intermediate, , was metastable and underwent disproportionation to and Zr, which was responsible for the detection of Zr metal in the potentiostatic reduction at less negative potentials. In the anodic scan, four main oxidation processes were observed. The relevant reactions were rationalized as the reoxidation of (iii) to , (iv) Zr to , (v) Zr to , and (vi) Zr to . The metastable intermediate also contributed to the unique current variations in the anodic potential scans under different conditions. Potentiostatic electrolysis of the powder in the MCE at the feature potentials of the CVs and analyses of the electrolysis products by scanning electron microscopy and energy dispersive X-ray spectroscopy confirmed the electroreduction mechanism and revealed the localized conversion of the dense aggregates of the submicrometer particles of to cauliflower-like aggregates of the nanoparticulates of Zr in the early stage of the electroreduction process.

Cyclic voltammetry of electroactive and insulative compounds in solid state: A revisit of AgCl in aqueous solutions assisted by metallic cavity electrode and chemically modified electrode

A novel platinum cavity electrode (Pt-CE) was fabricated by drilling a small circular cavity (0.5 mm diameter) through a thin Pt foil ( ca. 0.15 mm thickness, 2.0 mm width). It was used to record cyclic voltammograms (CVs) of the insulative AgCl powder (as a model) in aqueous solutions. The voltammetric response of the electrode was fast (tested to 100 mV/s) and the charge under the reduction peak agreed well with the mass of the AgCl powder. Further, the CVs were featured by not only an “irreversible” reduction peak, but also linear logarithm correlations between the potential scan rate and the reduction peak current or potential. Similar results were also obtained from thin AgCl coating modified Ag disc electrodes (1.0 mm diameter) formed by anodisation in chloride solutions. Based on these common electrode kinetic properties, a general explanation is proposed according to the mixed control of the electro-reduction by charge transfer at the conductor/insulator/electrolyte three phase interlines and mass diffusion through the reduction generated porous metal layer. In addition, some CVs also exhibited a minor reduction peak at less negative potentials and the origin was identified experimentally.