Perforated Electrode Research Articles

A perforated CMOS microchip for immobilization and activity monitoring of electrogenic cells

CMOS-based microelectrode systems offer decisive advantages over conventional micro-electrode arrays, which include the possibility to perform on-chip signal conditioning or to efficiently use larger numbers of electrodes to obtain statistically relevant data, e.g., in pharmacological drug screening. A larger number of electrodes can only be realized with the help of on-chip multiplexing and readout schemes, which require integrated electronics. Another fundamental issue in performing high-fidelity recordings from electrogenic cells is a good electrical coupling between the cells and the microelectrodes, in particular, since the recorded extracellular signals are in the range of only 10–1000 µV. In this paper we present the first CMOS microelectrode system with integrated micromechanical cell-placement features fabricated in a commercial CMOS process with subsequent post-CMOS bulk micromachining. This new microdevice aims at enabling the precise placement of single cells in the center of the electrodes to ensure an efficient use of the available electrodes, even for low-density cell cultures. Small through-chip holes have been generated at the metal-electrode sites by using a combination of bulk micromachining and reactive-ion etching. These holes act as orifices so that cell immobilization can be achieved by means of pneumatic anchoring. The chip additionally hosts integrated circuitry, i.e., multiplexers to select the respective readout electrodes, an amplifier with selectable gain (2×, 10×, 100×), and a high-pass filter (100 Hz cut-off). In this paper we show that electrical signals from most of the electrodes can be recorded, even in low-density cultures of neonatal rat cardiomyocytes, by using perforated metal electrodes and by applying a small underpressure from the backside of the chip. The measurements evidenced that, in most cases, about 90% of the electrodes were covered with single cells, approximately 4% were covered with more than one cell due to clustering and approximately 6% were not covered with any cell, mostly as a consequence of orifice clogging. After 4 days of culturing, the cells were still in place on the electrodes so that the cell electrical activity could be measured using the on-chip circuitry. Measured signal amplitudes were in the range of 500–700 µV, while the input-referred noise of the readout was below 15 µVrms (100 Hz–4 kHz bandwidth). We report on the development and fabrication of this new cell-biological tool and present first results collected during the characterization and evaluation of the chip. The recordings of electrical potentials of neonatal rat cardiomyocytes after several days in vitro, which, on the one hand, were conventionally cultured (no pneumatic anchoring) and, on the other hand, were anchored and immobilized, will be detailed.

Effect of perforated transparent electrodes on light transmittance and light scattering in substrates used for microcrystalline silicon thin-film solar cells

The effect of a perforated transparent electrode, which is an electrode punctuated with holes, on light transmittance and light scattering was studied using textured ZnO:Ga formed by wet etching. The perforations were found to play a role not only in improving transmittance but also in maintaining high haze factor. The influence of the surface morphology of textured ZnO:Ga on the growth of hydrogenated microcrystalline silicon and on solar cell performance was also studied. It was found that, while the ZnO:Ga surface is not steep, a height difference is present on the substrate surface at the edge of the perforations. To resolve this problem, an additional thin ZnO:Ga layer was deposited on a substrate which already had a perforated transparent electrode. Improvements in solar cell performance were obtained while high open circuit voltage and high fill factor were maintained.

Characterisation of a laboratory electrochemical ozonation system and its application in advanced oxidation processes

An electrochemical reactor for oxygen/ozone production was developed using perforated planar electrodes. An electroformed $$\beta$$ -PbO2 coating, deposited on a platinised titanium substrate, was employed as anode while the cathode was a platinised titanium substrate. The electrodes were pressed against a solid polymer electrolyte to minimise ohmic drop and avoid mixing of the gaseous products (H2 and O2/O3). Electrochemical ozone production (EOP) was investigated as function of current density, temperature and electrolyte composition. Electrochemical characterisation demonstrated ozone current efficiency, ΦEOP, ozone production rate (g h−1), $$\nu_{\rm EOP}$$ , and grams of O3 per total energy demand (g h−1 W−1), $$\nu_{\rm EOP}$$ increase on decreasing electrolyte temperature and increasing current density. The best reactor performance for EOP was obtained with the base electrolyte (H2SO4 3.0 mol dm−3) containing 0.03 mol dm−3 KPF6. Degradation of reactive dyes used in the textile industry (Reactive Yellow 143 and Reactive Blue 264) with electrochemically-generated ozone was investigated in alkaline medium as function of ozone load (mg h−1) and ozonation time. This investigation revealed ozonation presents very good efficiency for both solution decolouration and total organic carbon (TOC) removal.

Application of Freestanding Perforated Diamond Electrodes for Efficient Ozone-Water Production

The application of diamond electrodes is promising for electrolyzing water to produce ozone because of their superior chemical and dimensional stability, as well as their large overpotential for the oxygen evolution reaction. A freestanding conductive diamond plate was perforated to prepare a freestanding perforated diamond electrode, which was incorporated into a zero-gap electrolytic cell for direct electrochemical ozone-water production. This system has many advantages, in particular, that it exhibits the highest current efficiency (29%) reported for the electrochemical ozone-water production thus far.

Electrochemical cementation of offshore calcareous soil

The electrochemical stabilization processes are studied in a calcareous soil recovered from the Western Australia coast and on the interface of calcareous soil and steel foundation. A series of experiments are performed to study the effects of two chemical agents used in electrochemical stabilization tests. The strengthening effects of electro kinetics and electrochemical treatments on the calcareous soil are investigated first. Significant increases in the undrained shear strength and effective cohesion are obtained after all tests, and the most significant improvement is found after the electrochemical treatment using a 15% CaCl2 solution as the stabilization agent. Subsequently, an electrochemical test is carried out on the calcareous soil with an embedded steel plate to simulate a part of a caisson foundation, using CaCl2 as the stabilization agent. In this test, the practical considerations for later large-scale tests and ultimately for field implementation are taken into account in the design, including factors such as the attachment of electrodes to the foundation, injection of the stabilization agent via perforated pipe electrodes, and distributions of voltage and electrical current in the soil. The result of this test reveals a 700% increase in the steel plate axial load capacity after 7 days of treatment with an applied voltage of 4 V. The main features of the approach are that it generates virtually no disturbance to the soil and the treatment is targeted at the soil–structure interface. With further development, the electrochemical treatment may be applied in offshore engineering for stabilization of foundations installed in weak calcareous soils.Key words: calcareous soil, offshore foundations, soil improvement, chemical stabilization, electrokinetics.

Efficiency study of perforated diamond electrodes for organic compounds oxidation process

The electrochemical oxidation of organic compound by bulk electrolysis has been analyzed for diamond electrodes used as anode. Boron-doped diamond thin films were grown on titanium alloy substrates (Ti6Al4V) with a geometric area of 12.2 cm 2 at 870 K and at 6.5×10 3 Pa. By using hot filament chemical vapor deposition technique and perforated and non-perforated substrates, the films were grown in both sample sides. The electrodes were characterized from their electrochemical behavior as a function of film quality, morphology and surface area, for boron concentrations of approximately 10 18/cm 3. The electrode performance was determined by cyclic voltammetry measurements in acid and neutral solutions and the reversibility behavior of the Fe(CN) 6 3−/4− at the Ti6Al4V/diamond electrode were also studied. High performance liquid chromatography (HPLC) and total organic carbon (TOC) techniques were used to study the oxidation products. These techniques are important to quantify the different compounds in the oxidation process steps permitting to observe the diamond electrodes efficiency. The results have shown a TOC decrease of approximately 85% and for HPLC it was observed almost complete phenol combustion to CO 2. Scanning electron microscopy and Raman scattering spectroscopy were also used for morphology and diamond quality evaluation, respectively.

Remote plasma-enhanced chemical vapour deposition of silicon nitride at atmospheric pressure

Silicon nitride films were deposited using an atmospheric pressure plasma source. The discharge was produced by flowing nitrogen and helium through two perforated metal electrodes that were driven by 13.56 MHz radio frequency power. Deposition occurred by mixing the plasma effluent with silane and directing the flow onto a rotating silicon wafer heated to between 100°C and 500°C. Film growth rates ranged from 90±10 to 1300±130 Å min-1. Varying the N2/SiH4 feed ratio from 55.0 to 5.5 caused the film stochiometry to shift from SiN1.45 to SiN1.2. Minimum impurity concentrations of 0.04% carbon, 3.6% oxygen and 13.6% hydrogen were achieved at 500°C, and an N2/SiH4 feed ratio of 22.0. The growth rate increased with increasing silane and nitrogen partial pressures, but was invariant with respect to substrate temperature and rotational speed. The deposition rate also decreased sharply with distance from the plasma. These results combined with emission spectra taken of the afterglow suggest that gas-phase reactions between nitrogen atoms and silane play an important role in this process.

Mass transfer conditions on a perforated electrode support vibrating in an electrolytic cell

The limiting current data are measured at copper microelectrodes fixed flush with the surface of an electrode support—a square perspex plate. The data are obtained by vibrating the electrode support in an electrolytic cell using electrochemical method. The variables covered in this study are amplitude, frequency and diameter of the perforation on the electrode support. The electrolyte is 0.01 N potassium ferricyanide, 0.01 N potassium ferrocyanide and 0.5 N sodium hydroxide. It is found that the limiting current increased with increased frequency and amplitude. The limiting current decreased with increase in the diameter of the perforation.

Perforated Microelectrode Arrays Implanted in the Regenerating Adult Central Nervous System

Adult mammalian optic nerve axons are able to regenerate, when provided with the permissive environment of an autologous peripheral nerve graft, which is usually the sciatic nerve. This study demonstrates the ability of adult rat optic nerve axons to regenerate through the preformed perforations of a polyimide electrode carrier implanted at the interface between the proximal stump of the cut optic nerve and the stump of the peripheral nerve piece used for grafting. Evidence that retinal ganglion cells regenerated their axons through the perforated electrode carrier was obtained by retrograde labeling with a fluorescent dye deposited into the sciatic nerve graft beyond the nerve–carrier–nerve junction. The number of regenerating cells could be enhanced by injecting neuroprotective drugs like aurintricarboxylic acid and cortisol intravitreally. A second line of evidence was obtained by immunohistochemical staining with antibodies to neurofilament. Third, electrical activity of the regenerating nerves was recorded after stimulating the retina with a flash of light. The results suggest that a regenerating central nerve tract may serve as an experimental model to implant artificial microdevices to monitor the physiological and topographical properties of neurites passing through the device or to stimulate them, thus interfering with their potential to grow. This study reports for the first time that the optic nerve has unique properties, which aids in the realization of these goals.

Long-term plasticity in interneurons of the dentate gyrus.

Single interneurons influence thousands of postsynaptic principal cells, and the control of interneuronal excitability is an important regulator of the computational properties of the hippocampus. However, the mechanisms underlying long-term alterations in the input-output functions of interneurons are not fully understood. We report a mechanism of interneuronal plasticity that leads to the functional enhancement of the gain of glutamatergic inputs in the absence of long-term potentiation of the excitatory synaptic currents. Interneurons in the dentate gyrus exhibit a characteristic, limited (approximately 8 mV) depolarization of their resting membrane potential after high-frequency stimulation of the perforant path. The depolarization can be observed with either whole-cell or perforated patch electrodes, and it lasts in excess of 3 h. The long-term depolarization is specific to interneurons, because granule cells do not show it. The depolarization requires the activation of Ca(2+)-permeable alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and the rise of intracellular Ca(2+), but not N-methyl-d-aspartate (NMDA) receptor activation. Data on the maintenance of the depolarization point to a major role for a long-term change in the rate of electrogenic Na(+)/K(+)-ATPase pump function in interneurons. As a result of the depolarization, interneurons after the tetanus respond with action potential discharges to previously subthreshold excitatory postsynaptic potentials (EPSPs), even though the EPSPs are not potentiated. These results demonstrate that the plastic nature of the interneuronal resting membrane potential underlies a unique form of long-term regulation of the gain of excitatory inputs to gamma-aminobutyric acid (GABA)ergic neurons.

Location of hydrogen gas evolution on perforated plate electrodes in zero gap cells

Abstract It is shown experimentally that the gas produced on perforated plate electrodes in water electrolysis cells is generated in the gap between the electrode and the diaphragm. Under a minimum diameter of the perforations no gas evolution is observed; the bubbles block the perforations. For hydrogen evolving electrodes, this minimum diameter is about 200 μm. The gap between the diaphragm and the electrode should be of the same order of magnitude.

Microparticle separation on a perforated electrode in a nonuniform electric field

We solve the problem of passage of microparticles through a perforated electrode under conditions of their electrodynamic fluidization (EDF) in a nonuniform electric field. It is shown that when the particle size is considerably smaller than the perforated hole size, microparticle sizing takes place in the region under the electrode. We report the experimental data.

Experimental Study of EHD Heat Exchanger for Nonazeotropic Mixtures.

To realize higher performance heat pump systems utilizing nonazeotropic mixtures, the EHD (Electrohydrodynamic) evaporator and condenser have been experimentally studied. Conventionally manufactured surfaces have not been effective for the evaporation and the condensation of nonazeotropic mixtures because of the accumulation of less evaporative or less condensable components of the mixture near the heat transfer surface. By setting the perforated coaxial cylindrical electrode inside of the 3.75-m-long evaporator tube, the evaporation and boiling heat transfer of the nonazeotropic mixture of HCFC 123 and HFC 134a on the inner surface of the tube have been enhanced by the factor of about 3 times over a wide range of qualities with the application of 7 kV at the electrode distance of 2.5 mm. Furthermore, using the electrically conducting transparent glass, it was clarified that the flow pattern has been changed and that some EHD phenomena such as the EHD surface instability have been observed. As for the condenser, the necessary tube length for condensation outside of the vertical tube has been shortened by two kinds of EHD effects, the increase of the condensation surface and the realization of the thinner film of the condensate.

Preparation and use of Raney-Ni activated cathodes for large scale hydrogen production

Raney-Ni catalysts, which are operated in technical electrolysis plants for cathodic hydrogen evolution and which are applied to the electrode structure by different means, were tested with respect to their catalytic activity under industrial conditions in an undivided cell. It was shown that in contrast to other catalysts an additional overvoltage occurred with rolled Raney-nickle due to smaller bubble radii (some μm). Concerning the design of technical electrodes one can conclude that louvered electrodes exhibiting heights of the single stripe up to 15 cm are equivalent to the normally used expanded mesh—or perforated electrodes with respect to their performance and cell resistance. With respect to construction and fabrication engineering they exhibit distinct advantages, which lead to significant cost reductions for electrolysis plants.

Bubble Effects on the Terminal Voltage of a Vertical Cell with Perforated Electrodes

Effect of bubbles on terminal voltage, solution IR‐drop, and overvoltage in a vertical cell with perforated electrode were investigated. Cell voltage was minimized by use of properly designed perforated electrode. Reduction of the surface area of such machined electrodes is an important disadvantage. With the experimental results obtained, an optimum was estimated to be in the range of 5–15% perforation depending on the current and the rate of gas evolution.

Device for deformation-free electrolytic etching of thin specimens

An easily constructed device is described that ensures deformation-free electrolytic etching of thin (μm range) specimens and avoids elaborate and time-consuming procedures. Essentially the device consists of a perforated electrode on which the specimen is held by maintaining a low pressure underneath. In addition the description of a valve assembly is given which is used for the recycling of the electrolyte that is sucked out of the bath through the holes in the electrode.

Discharge Tube with Transparent Hollow Cathode

Abstract In some cases the spectroscopic investigation of electrode phenomena in the plasma and of the plasma itselt is hampered by the nontransparency of the metal electrodes. The use of perforated electrodes is not very expedient and is only a partial solution. The same problem arises in the cases of spectral investigations of the discharge in hollow cathode. The aim of the present communication is to give a possibility to replace the metal electrodes with conductive transparent layer.

Electromechanical suppression of a demand pacemaker associated with electrode perforation

Electromechanical inhibition of a demand pacemaker is reported due to the contact of two perforated right ventricular endocardial pacemaker electrodes. Electrode contact occurring during ventricular systole was verified at surgery. In vitro suppression of the demand function of a powerpack was accomplished by intermittently tapping two electrodes and generating an effective electrical signal.

Design and Performance of a High-Frequency Electrostatic Speaker

An electrostatic speaker has been developed which provides a high quality of high-frequency reproduction not available with electromagnetic tweeters. The diaphragm consists of a thin plastic film bearing an evaporated metallic layer. The membrane is stretched around a semicylindrical perforated electrode on which ridges are embossed to provide clearance. The response varies less than ±2 db in the frequency range between 8 and 16 kc. The azimuthal distribution pattern is excellent, owing to the cylindrical geometry, and is essentially independent of frequency in the same range. The second harmonic distortion inherent in this type of speaker is maintained at a low value. An indication of the quality of high-frequency reproduction is provided by oscillograms of the response to tone burst signals. The speaker is in quantity production and has been incorporated in several models of home reproduction instruments.

Physicochemical investigation of a cation exchange resin (amberlite IR100) II. Resin conductance

1. 1. The electric conductivity of swollen resin plugs packed between perforated platinum electrodes, and containing various bound cations, is investigated in a special streaming cell, which allows of replacement of one ionic species by another in the same plug. This method proves to be a useful tool in the investigation of the strength of binding of cations in the resin. 2. 2. The hydrogen resin is a fairly good conductor; the conductance of alkali metal resins is about 6–12 times smaller, while resins in which hydrogen is replaced by ions of higher valency, or silver, are poor conductors. For hydrogen and alkali metal resins, the resin conductance is roughly proportional to the mobility of the respective cations in water, but no such proportionality exists for resins containing silver or ions of higher valency. It is concluded that the latter are much more tightly bound than the former, the order being Th 4+>La 3+>>Ba ++>Ag +>Ca ++>>Mg ++>>alkali metal ions > H + 3. 3. The variation of the resistance of plugs of alkali metal resins with the pH of the salt solution used in the exchange reaction is studied. The resistance has a maximum at pH ⋍ 3.5 but falls when the pH of the salt solution is higher. It is suggested that up to pH ⋍ 3.5 the -SO 3H groups are involved, but that groups of a more weakly acid nature come into action at higher pH. There is evidence of hydrolysis of alkali metal salts of the latter groups on streaming water through the resin plug.