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PubMed1978

Volume changes and potential artifacts of epithelial cells of frog skin following impalement with microelectrodes filled with 3 m KCl.

Cells of isolated frog skin epithelium were observed microscopically during impalement with standard microelectrodes of 5 to 20 Momega resistance, filled with 3 m KCl. Impaled cells, as well as some neighboring cells, were seen to swell 10 to 100 sec after impalement, while the negative potential recorded by the microelectrode depolarized (open circuit conditions). Apparently, osmotic swelling of small epithelial cells may be caused by diffusion of KCl from such electrodes. This conclusion is supported by calculations quoted from the literature of KCl loss from microelectrodes. Intracellular recordings from epithelia with destructed cellular membranes gave negative "pre-tip potentials" of up to mV. The potentials could be altered by electrode movement, by decreasing the ambient pH or the tip-pH and by modifying the fixed charges of the tissue chemically. It is shown that even a moderate loss of KCl, which will not result in appreciable swelling, can produce negative potentials in front of the electrode tip if the protoplasm has a high density of negative fixed charges. We suggest the use of 3 m KCl electrodes with resistances above 30 Momega if after impalement compression of intracellular material by the tip can be avoided. Where such compression cannot be avoided, it is best to fill the microelectrode with an isotonic solution which mimics the electrolyte composition of the cytosol.

Animals↗

PubMed1985

Comparative measurements of potassium and chloride with ion-sensitive microelectrodes and x-ray microanalysis in cultured skeletal muscle fibers.

Data of the intracellular electrolyte concentration of potassium and chloride in cultured muscle cells measured by x-ray analysis were compared by using the different activity coefficients with intracellular potassium and chloride activities measured with double-barrelled microelectrodes. By using an activity coefficient of 0.6, 95% of the potassium microelectrode measurements are in accordance with the x-ray analysis values, in spite of a scattering of the values. Membrane potential and intracellular potassium values are linearly related. x-ray analysis and ion-sensitive microelectrodes measured the cytoplasmic chloride in the same range. Taking into account known activity coefficients, an error of 25% must be assumed with the intracellular chloride measurements. However, x-ray analysis and ion-sensitive microelectrode investigations are reliable tools to study intracellular potassium and chloride changes, which play an important role in membrane characteristics.

Animals↗

PubMed2002

Microelectrode-guided technique for treatment of Parkinson's diseases.

From May, 2000 to June, 2001, 27 patients with Parkinson disease (PD), including 10 cases of rigidity, 13 cases of tremor, 4 cases of rigidity and tremor, were treated by microelectrode-guided technique. Among them, phlebotomy was carried out in 17 cases and thalamotomy in 10 cases. All the targets of lesion were anatomically located by using MR and neurophysiological signals on microelectrode. Our results showed that the efficiency of microelectrode-guided technique for treatment of PD was 98%. The postoperative unified parkinson disease rating scale were 12.3 +/- 9.1 and 13.2 +/- 8.9 respectively, which significantly improved as compared with those before operation. It was concluded that by recognizing special electrical signals in neurons microelectrode-guided neuropsychological techniques can locate target at cellular level, which overcomes the individual difference in anatomy and function, and allow more accuracy, safety and efficiency of operation. This is especially true of PD patients who fail to respond to medical treatment.

Adult↗

PubMed2004

Overcoming the problem of non-ideal liquid ion exchanger selectivity in microelectrode ion flux measurements.

Ion-selective microelectrodes are a powerful tool in studies on various aspects of cell membrane biology in both animal and plant tissues. Further application of this technique is, however, limited to a large extent by the problem of non-ideal selectivity of the liquid ion exchanger used in the preparation of microelectrodes for ion flux measurements. Because of this problem, which is persistent in many commercial liquid ion exchangers, the microelectrode does not discriminate between the ion of interest and other interfering ions (for example, Mg2+ and Ca2+; Na+ and K+), thereby leading to inaccurate concentration readings and, consequently, inaccurate flux calculations. In this work we show that the existing analytical procedure to overcome this problem, using the inverted Nicolsky-Eisenman equation, is inadequate, and suggest an alternative analytical procedure that can be applied directly to the data obtained with commercially available liquid ion exchangers. We show that this alternative procedure allows accurate measurement of ionic concentrations with non-ideal ion-selective microelectrodes in the presence of interfering ions, and illustrate the method by direct experiment using Ca2+ and Mg2+ as a "case study". Several more examples are given, further illustrating practical applications of the method for study of plant responses to salinity, osmotic and reactive oxygen species stresses.

Algorithms↗

PubMed2005

Electrophysiological and histological studies of chronically implanted intrapapillary microelectrodes in rabbit eyes.

PURPOSE: To determine the safety and efficacy of transsclerally placed intrapapillary wire microelectrodes implanted chronically into the optic nerve head of rabbit eyes. METHODS: Four platinum wire microelectrodes were passed through the sclera and implanted into the optic nerve head of five rabbit eyes for 4-6 months. Color fundus photography, fluorescein angiography, electroretinograms (ERGs), and visually evoked potentials (VEPs) were used to monitor the retina. Electrically evoked potentials (EEPs) were elicited by bipolar electrical stimulation of the optic nerve axons by different combinations of the four electrodes immediately after the implantation and at 1-month intervals thereafter. The effects of the chronic implantation of the electrodes on the morphology of the optic nerve were evaluated by histological and immunohistochemical examinations at 4 and 6 months after the implantation. RESULTS: All of the electrodes remained stable in the implanted sites throughout the post-implantation period, except for one electrode that had pulled out of the optic nerve head at 1 month after implantation. No intraocular infection, inflammation, or vitreoretinal proliferation was observed in any eye. EEPs could be elicited from each pair of electrodes at all testing times. The mean threshold currents (charge densities) to evoke EEPs increased from 19.3 +/- 9.2 microA (6.0 +/- 2.9 microC/cm2) on the implantation day to 78.8 +/- 31.9 microA (24.6 +/- 10.0 microC/cm2) at 1 month after implantation, but did not change significantly thereafter. The implicit time and amplitude of the a- and b-waves of the ERGs and of P1 of the VEPs did not change significantly throughout the post-implantation period. Histological evaluation of the optic nerve head revealed slight tissue encapsulations surrounding the electrode and increased expression of glial fibrillary acidic protein near the surface of the optic nerve. CONCLUSIONS: Implantation of transscleral intrapapillary microelectrodes appears to be safe and effective. These findings indicate that the implantation of microelectrodes in the optic nerve head should be considered for an optic nerve-based prosthesis.

Animals↗

PubMed1990

Biphasic voltage relaxation pattern observed in cells of Eremosphaera viridis after injection of charge-pulses of short duration: detection of tip clogging of intracellular microelectrodes by charge-pulse technique.

Charge pulse experiments performed on the peat-bog alga Eremosphaera viridis revealed an unusual voltage relaxation behaviour. Injection of charge pulses of 1 microseconds duration resulted in an immediate charging of the membranes (time constant of the order of 40 ns). Nevertheless, the potential-measuring microelectrode recorded an exponential increase in membrane voltage with a time constant of about 1.3 ms. The maximum voltage value was recorded after about 3 ms, followed by an exponential decay with a time constant of about 9.6 ms. This biphasic time course was independent of the amplitude of the injected charge and of the location of the impaled microelectrodes in the vacuole. Centrifuged cells in which the chloroplasts and the other organelles were pelleted in one part of the cells showed the same electrical response. Electrical breakdown of the cell membranes resulted in the disappearance of the biphasic voltage response. In this case only the decaying relaxation process could be recorded with a time constant of 3 ms. After resealing of the membranes the original biphasic relaxation response was restored. Increasing concentrations of KCl in the bathing medium reduced both time constants almost correspondingly. The experimental findings were evaluated with an electrical equivalent circuit. Theoretical analysis with reference to the experimental data suggested that the delayed voltage response of the potential-recording electrode resulted from a membrane seal across the tip of this electrode. The resistance of this seal was calculated to be about 400 M omega. The specific resistances and capacitances of tonoplast and plasmalemma membranes were calculated from the decaying part of the biphasic relaxation curves. The average values were found to be 2.58 omega.m2 and 5 mF.m-2. The investigations reported here suggest that charge pulse experiments can be generally used for the detection of membrane and cytoplasmic material clogging of the tip of intracellular microelectrodes, a problem with which most electrophysiologists are faced when interpreting data obtained from impaled microelectrodes.

Cell Membrane↗

PubMed1986

Neuronal activity evoked by chronically implanted intracortical microelectrodes.

The averaged evoked compound action potentials (AECAPs) were recorded from the ipsilateral pyramidal tract of awake, unrestrained cats before, during, and after continuous electrical stimulation of the cerebral cortex via chronically implanted activated iridium or platinum-30% iridium (Pt30%Ir) microelectrodes. After stimulating 24 h at 20 pulses per second (pps), using charge-balanced, 200-microseconds pulse pairs of 40 to 80 microA (400 to 800 microC/cm2, 8 to 16 nC/phase (ph), 2 to 4 A/cm2), there was a transient elevation of the threshold of the early (direct) and of the alte (transynaptic) components of the AECAP. After cessation of continuous stimulation at 80 microA, the threshold of the early component of the AECAP remained elevated for as long as 24 h and the late component as long as 4 days, indicating significant but reversible depression of the electrical excitability of cortical neurons close to the microelectrodes. In three cats stimulated 23 h/day for 1 week, the AECAP also recovered to their prestimulus threshold. In contrast, pulsing for 24 h at 320 microA (3200 microC/cm2, 64 nC/ph, 16 A/cm2) produced marked elevation of the threshold of the AECAPs which was not reversed by 7 to 12 days after termination of intracortical stimulation. The electrical excitability of neurons adjacent to (unpulsed) microelectrodes 2 mm from the pulsed electrode was not affected. The observations reported here, in conjunction with the histologic results reported in the companion paper, indicate that both the Pt30%Ir and the iridium microelectrodes can be operated safely at currents to at least 80 microA, charge/ph of 16 A/cm2, and a charge density of 800 microC/cm2 X ph. However, on the basis of the electrophysiologic criteria, both types appear to be unsafe when pulsed at 320 microA (64 nC/ph, 3200 microC/cm2 X ph, 16 A/cm2).

Action Potentials↗

PubMed1994

A new method for manufacturing carbon-fibre microelectrodes.

A new, fast and low-cost method using a carbon-fibre microelectrode is proposed. The microelectrode is constructed by glueing one or more carbon fibres (5 mm in diameter) with a silver resin on a silver wire or stainless steel tube. The characteristics of that microelectrode have been measured and compared with those of commercially available glass carbon-fibre microelectrodes. According to our measures, the impedance, capacity and current noise were lowered which permits these electrodes to be used in voltammetry and in detection of very low currents generated during formation of antigen-antibody complex.

Carbon↗

PubMed1989

An ion-selective microelectrode for bile salts.

The development of a prototype ion-selective microelectrode for bile salts is described. The microelectrodes demonstrated Nernstian response (59 +/- 10 mV dec-1) with sodium deoxycholate in Tris (0.2 M, pH 9.0, 15-30 degrees C), HEPES (0.13 M, pH 7.5), and bicarbonate buffers (0.1 M, pH 7.5) (25 +/- 0.1 degrees C) were stable for several days, and the responses were highly reproducible. The microelectrodes were selective for bile salts over the physiologically important inorganic anions, bicarbonate and chloride. The response to sodium cholate (42 mV dec-1) was consistently lower than the ideal response (59 mV dec-1). This ion-selective microelectrode may show promise as a useful tool for the determination of intracellular bile salt activity.

Bile Acids and Salts↗

PubMed2004

Neuronal differentiation and synapse formation of PC12 and embryonic stem cells on interdigitated microelectrode arrays: contact structures for neuron-to-electrode signal transmission (NEST).

The development of neuron-microelectrode interfaces (neurochips) is highly desirable for the non-invasive recording of the cellular response to neuroactive drugs as well as the electrical stimulation of nervous tissue by implantable electrodes. A prerequisite for neuron-to-electrode signal transmission (NEST) is the formation of synapse-like contacts between the neuronal cell and the conductive surface of a microelectrode array. We attempted synapse formation by neuronal differentiation of rat pheochromocytoma cells (PC12) and blastocyst-derived murine embryonic stem cells (ES-J1) on interdigitated microelectrode arrays that were made of gold (Au), platinum (Pt), or indium tin oxide (ITO). PC12 or ES cells were in vitro differentiated by incubation with nerve growth factor (NGF) and forskolin, or by serum deprivation and treatment with basic fibroblast growth factor (FGF-2), respectively. On top of ITO electrodes, the neuronal cells extended extremely long processes that terminated in pili-like contact structures, which is typical for growth cone formation. ES cells differentiated into neurons as verified by immunofluorescence staining of MAP-2 and developed synapse-like junctions with the ITO electrode surface as indicated by synaptophysin staining. Differentiated PC12 and ES cells showed bona fide morphological characteristics of synaptic growth cones that were unprecedented in tissue culture. Cones formed by PC12 cells could be stimulated with KCI and carbachol as shown by uptake of FM1-43, a fluorescent marker for synaptic vesicle formation. In contrast to Electrical Cell Impedance Spectroscopy (ECIS) recordings, AC impedance spectrometry with differentiated PC12 cells settled on interdigitated microelectrode arrays revealed lower AC impedance than that with undifferentiated cells, indicating that the complex impedance is dependent on ion fluxes at the neuron-to-electrode contact surface.

Animals↗

PubMed2004

Flexible polyimide probes with microelectrodes and embedded microfluidic channels for simultaneous drug delivery and multi-channel monitoring of bioelectric activity.

The study of intracellular communication requires devices that can not only monitor the bioelectric activity, but also control and observe the biochemical environment at the cellular level. This paper reports on the development and characterisation of implantable polyimide microprobes that allow simultaneous, selective chemical delivery/probing and multi-channel recording/stimulation of bioelectric activity. The key component of the system is a flexible polyimide substrate with embedded microchannels that is batch-fabricated combining polyimide micromachining and a lamination technique. The devices provide platinum microelectrodes on both sides of the polyimide substrate with an active surface between 20 microm x 20 microm and 50 microm x 50 microm. The embedded microchannels permit highly localised drug delivery or probing at the tip of the device via channel outlets adjacent to the microelectrodes. The microelectrodes were characterised by electrical impedance spectroscopy and the microchannels were studied in microflow experiments. Two different fluid delivery schemes were explored in two different designs. The first device type consists of a simple combination of microchannels and microelectrodes on one substrate. Liquids are ejected at the tip of the device by pressure injection techniques. The second device was inspired by the so-called U-tube concept allowing for highly localised delivery of controlled amounts of liquids in the picoliters range. Thus, the influence of chemical compounds on the electrical activity of cells can be studied with high temporal and spatial resolution. The flexible, implantable devices can be used for studying the chemical and electrical information exchange and communication of cells in in vivo and in vitro experiments.

Biosensing Techniques↗

PubMed2004

CMOS microelectrode array for the monitoring of electrogenic cells.

Signal degradation and an array size dictated by the number of available interconnects are the two main limitations inherent to standalone microelectrode arrays (MEAs). A new biochip consisting of an array of microelectrodes with fully-integrated analog and digital circuitry realized in an industrial CMOS process addresses these issues. The device is capable of on-chip signal filtering for improved signal-to-noise ratio (SNR), on-chip analog and digital conversion, and multiplexing, thereby facilitating simultaneous stimulation and recording of electrogenic cell activity. The designed electrode pitch of 250 microm significantly limits the space available for circuitry: a repeated unit of circuitry associated with each electrode comprises a stimulation buffer and a bandpass filter for readout. The bandpass filter has corner frequencies of 100 Hz and 50 kHz, and a gain of 1000. Stimulation voltages are generated from an 8-bit digital signal and converted to an analog signal at a frequency of 120 kHz. Functionality of the read-out circuitry is demonstrated by the measurement of cardiomyocyte activity. The microelectrode is realized in a shifted design for flexibility and biocompatibility. Several microelectrode materials (platinum, platinum black and titanium nitride) have been electrically characterized. An equivalent circuit model, where each parameter represents a macroscopic physical quantity contributing to the interface impedance, has been successfully fitted to experimental results.

Action Potentials↗

PubMed2005

Compatibility of glass-guided recording microelectrodes in the brain stem of squirrel monkeys with high-resolution 3D MRI.

Knowledge of the precise position of recording microelectrodes within the brain of a non-human primate is essential for a reliable exploration of very small anatomic structures. This work demonstrates the compatibility of a newly developed glass-guided microelectrode design and microfeed equipment with high-resolution 3D magnetic resonance imaging (MRI). T1- and T2-weighted images allow for the non-invasive visualization of chronically implanted microelectrodes within the brain stem of squirrel monkeys in vivo. Neural extracellular multi-unit recordings proved the functionality of the microelectrode before and after the use of 3D MRI suggesting the preservation of normal brain tissue at the tip of the electrode. Because histology confirmed the absence of lesions attributable to MRI, the approach offers an interactive monitoring during the course of neuroethological experiments. Consequently, MRI may become an in vivo alternative to common histological post mortem verifications of electrode tracks and hence may avoid the early sacrificing of primates after only a small number of experiments.

Action Potentials↗

PubMed1980

Resistive artifacts in liquid-ion exchanger microelectrode estimates of Na+ activity in epithelial cells.

In experiments on the rabbit urinary bladder epithelium we have identified an electrical artifact in certain liquid ion-sensitive microelectrodes. This artifact arises from the high electrical resistance of the ion-sensitive resins which in some cases are comparable to the resistance of the microelectrode glass wall. For Na+-sensitive microelectrodes this situation led to shunting of the exchanger potential and consequently artifactually high calculations of intracellular Na+ in the rabbit urinary bladder epithelium. A method for minimizing this shunting effect is described. After reduction of the shunt the frequency response of the Na+-sensitive microelectrode was increased and the estimated ai Na+ was decreased to 7 mM.

Animals↗

PubMed1996

Simultaneous measurements of intracellular pH in the leech giant glial cell using 2',7'-bis-(2-carboxyethyl)-5,6-carboxyfluorescein and ion-sensitive microelectrodes.

We have employed two independent techniques to measure the intracellular pH (pHi) in giant glial cells of the leech Hirudo medicinalis, using the fluorescent dye 2',7'-bis-(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF) and double-barreled neutral-carrier, pH-sensitive microelectrodes, which also record the membrane potential. We have compared two procedures for calibrating the ratio of the BCECF signal, excited at 440 nm and 495 nm: 1) the cell membrane was H(+)-permeabilized with nigericin in high-K+ saline at different external pH (pHo) values, and 2) the pHi of intact cells was perturbed in CO2/HCO3(-) -buffered saline of different pH, and the BCECF ratio was calibrated according to a simultaneous microelectrode pH reading. As indicated by the microelectrode measurements, the pHi did not fully equilibrate to the pHo values in nigericin-containing, high-K+ saline, but deviated by -0.12 +/- 0.02 (mean +/- SEM, n = 37) pH units. In intact cells, the microelectrode readings yielded up to 0.15 pH unit lower values than the calibrated BCECF signal. In addition, larger dye injections into the cells (> 100 microM) caused an irreversible membrane potential loss indicative of some damage to the cells. The amplitude and kinetics of slow pHi changes were equally followed by both sensors, and the dye ratio recorded slightly higher amplitudes during faster pHi shifts as induced by the addition and removal of NH4+.

Animals↗

PubMed2002

Electrochemical platinum coatings for improving performance of implantable microelectrode arrays.

The formation and properties of electrochemical platinum films grown on platinum contacts contained in implantable flexible microelectrodes were investigated. The resulting platinum deposits were obtained by applying cyclic voltammetry to baths containing concentrations around 70 mM of chloroplatinic acid. A pre-activation step was necessary before the platinum-electroplating step in order to achieve good adhesive properties. The benefits of this process were ascribed to higher corrosion resistance, lower impedance and improved adhesion to the sputtered platinum. These improvements can make the application of this electrochemical technique highly useful for increasing the lifetime of implantable microelectrode arrays, such as cuff structures (IEEE Trans. Biomed. Eng. 40 (1993) 640). These medical devices, obtained by semiconductor technology could be used for selective stimulation of nerve fascicles, although, poor long-term performance has been achieved with them. The dissolution rate for platinum thin-film microelectrodes under fixed corrosion test conditions was 38.8 ng/C. Lower rates were observed for electroplated microelectrodes, obtaining a dissolution rate of 7.8 ng/C under analogous experimental ageing conditions. The corrosion behaviour of the electroplated platinum during stimulation experimental conditions was estimated by electrochemical impedance spectroscopy.

Biocompatible Materials↗

PubMed1998

In vivo microelectrode track reconstruction using magnetic resonance imaging.

To obtain more precise anatomical information about cortical sites of microelectrode recording and microstimulation experiments in alert animals, we have developed a non-invasive, magnetic resonance imaging (MRI) technique for reconstructing microelectrode tracks. We made microelectrode penetrations in the brains of anesthetized rats and marked sites along them by depositing metal, presumably iron, with anodic monophasic or biphasic current from the tip of a stainless steel microelectrode. The metal deposits were clearly visible in the living animal as approximately 200 microm wide hypointense punctate marks using gradient echo sequences in a 4.7T MRI scanner. We confirmed the MRI findings by comparing them directly to the postmortem histology in which the iron in the deposits could be rendered visible with a Prussian blue reaction. MRI-visible marks could be created using currents as low as 1 microA (anodic) for 5 s, and they remained stable in the brains of living rats for up to nine months. We were able to make marks using either direct current or biphasic current pulses. Biphasic pulses caused less tissue damage and were similar to those used by many laboratories for functional microstimulation studies in the brains of alert monkeys.

Animals↗

PubMed1990

Copper determination in urine by flow injection analysis with electrochemical detection at platinum disk microelectrodes of various radii.

The incorporation of platinum disk microelectrodes of various radii (2.5-50 microns) in a well-jet flow cell offers reduced limits of detection for the determination of copper in urine by flow injection analysis compared with standard methods based on a conventional sized glassy carbon disk macroelectrode (radius 1.5 mm), in a thin-layer cell. The radius of the platinum disk microelectrode was found to be critical with respect to both the limit of detection and flow rate dependence. An optimal radius value of 28 microns was found with detection limits increasing with both larger and smaller electrode radii. In contrast, as theoretically expected, a diminished flow rate dependence was observed the smaller the radii of the platinum disk microelectrodes. Sample cleanup and preparation is conveniently achieved by the use of Sep-Pak cartridges and formation of a copper dithiocarbamate complex. The metal complex is easily oxidized at platinum disk microelectrodes in acetonitrile, which was the solvent used in the flow injection method of analysis.

Copper↗