Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Microelectrodes”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1980

General properties of antimony microelectrode in comparison with glass microelectrode for pH measurement.

Two kinds of pH-sensitive microelectrodes were constructed: 1) glass microelectrode with a pH-sensitive tip of 50--100 micrometers in length, and 2) antimony (Sb) microelectrode with a tip of 1--5 micrometers in outside diameter. Comparisons of the two were made on the change in the electromotive force (EMF) in response to various pHs and biological applicability. The pH sensitivity (slope constant) at 20 degrees C of the glass and Sb-microelectrodes averaged 51.7 and 51.9 (-mV/pH), respectively. Over the pH range of 2 to 9, both electrodes responded linearly to the change of pH. The pH-dependent EMF of the Sb-microelectrode was influenced by phosphate buffers, but not by Tris-HCl buffers. Through the glass microelectrode showed a linear response to all the buffers tested, its slope constant tended to be limited by the surface area of the pH-sensitive tip. The stability of the EMFs was well within 1 mV for 12 hr with the glass microelectrode but more than 10 mV with the Sb-microelectrode. One the other hand, the 95% response time was about 1 min with the glass microelectrode, whereas it was less than a few seconds with the Sb-microelectrode. Blood pH was measured with the two electrodes and reasonable values were obtained with both methods, although the values by use of the Sb-microelectrode were slightly higher than those of the other. In view of the practical ease of manufacturing, maintenance and durability, the use of the Sb-microelectrode in biological measurement should also be re-evaluated, but several restrictions must be imposed on it.

Animals↗
PubMed2002

Intraoperative microelectrode and semi-microelectrode recording during the physiological localization of the thalamic nucleus ventral intermediate.

We review the techniques of physiological localization of the site for ventralis intermedius (Vim) thalamotomy or implantation of Vim-deep brain stimulation (DBS) for treatment of parkinsonian, essential, and intention tremor. Both microelectrode and semi-microelectrode techniques are reviewed. We believe the use of microelectrode and semi-microelectrode recordings in combination with Radiological landmarks provide the most accurate localization of the target. In addition to recording, microstimulation of subcortical structures such as Vim and thalamic nucleus ventralis caudal through the microelectrode may improve physiological identification by altering the tremor and evoking somatic sensations, respectively. Microelectrode recording provides the highest resolution picture of the target site at a cost of increased time to locate the target. We also review the relationship between thalamic neuronal firing and electromyographic activity during tremor. Implications of these results for the mechanisms for parkinsonian, essential, and intention tremors are discussed.

Brain Mapping↗
PubMed1987

Microelectrode Measurements on Red Beet Vacuole : Biological Effect of Na OR NO(3) Ions, Diffusing from the Microelectrode.

Glass microelectrodes filled with 3 molar KCl are widely used to measure intracellular potentials and it is usual to try to minimize their electrolyte loss. In these experiments we have used the ionic leak of our microelectrodes, filled with various salt solutions, to introduce a given ion into the red beet vacuole. This allowed us to show that NO(3) (-) ions reduce the magnitude of the current spectral density while they do not change the resistance of the tonoplast. This is true when NO(3) (-) is either added to the external medium or used as the microelectrode filling solution. This can be interpreted by a NO(3) (-) effect on the vacuolar side of the tonoplast, resulting in an inhibition of the ion transporting ATPase. Replacing K(+) by Na(+) ions in the medium has no effect on tonoplast resistance (R(s)). On the contrary, when ions leaking from the microelectrode are H(+), Li(+) or K(+), R(s) is close to 4 kilohm square centimeter, whereas R(s) is of the order of 30KOmega square centimeter when Na(+) are the leaking ions. We also found a possible correlation between the presence of a Lorentzian in the current spectral density (cut-off frequency = 2 hertz) and a Cl(-) efflux from the vacuole. This could be explained by the existence of Cl(-) channels on the tonoplast.

Journal Article↗
PubMed1987

Quartz micropipettes for intracellular voltage microelectrodes and ion-selective microelectrodes.

We find that quartz is better than borosilicate glass as a material for micropipettes for certain microelectrode applications, including ion-selective microelectrodes of the liquid membrane type. Details are given of a graphite heating element that can be mounted on a standard microelectrode puller and used for making quartz micropipettes. A novel method of silanizing micropipettes is described. Experience with a novel miniature beveller that is fitted on a microscope stage is reported.

Electrophysiology↗
PubMed1992

Comparison of impedance at the microelectrode-saline and microelectrode-culture medium interface.

The impedance characteristics of gold-plated indium-tin-oxide microelectrodes immersed in culture medium (MEM) are described and compared with the impedance characteristics observed when those microelectrodes are immersed in isotonic saline. For microelectrode areas of approximately 100 microns2, applied voltage levels of 5, 50, and 100 mV, and for frequencies of from 100 Hz to 10 kHz the resistance, capacitance, capacitive reactance, and total impedance are given as a function of frequency both in culture medium and in saline. The results, which hold for current densities ranging from 0.45 to 700 pA/microns2, are compared. Also given are the alpha and K values determining the frequency characteristics of the interface resistance and capacitance in medium and in saline.

Culture Media↗
PubMed1990

A carbon dioxide air-gap microelectrode based on a neutral hydrogen ion exchanger pH microelectrode.

A relatively simple potentiometric pCO2 gas-sensing microelectrode is described. It is based on an ion-exchanger pH electrode, has a 2- to 5-microns tip, and has an air gap which is formed by means of hydrophobic treatments. The microelectrode exhibits a linear response in the range 10(-4)-10(-2) M with a Nernstian slope of 59 to 62 mV/decade at 25 degrees C. Ninety-five percent of the steady-state response time is about 20-30 s at the flow system when the concentration of sodium bicarbonate in buffer solution (pH 4.5) suddenly shifts from 0.2 to 2 mM and the lifetime is longer than 1 week.

Animals↗
PubMed1977

Modifications of glass microelectrodes: a self-filling and a semifloating glass microelectrode.

A simple and inexpensive method for constructing a double capillary was developed for preparing a self-filling glass microelectrode. The modified method uses a thin capillary instead of a bundle of glass fibers and fuses it to the outer capillary wall with flame before pulling the latter with a puller. The validity of the new electrode was proven by measuring the proximal cell PD of the rat kidney slices (mean of the stable cell PDs lasting longer than 30 min,--69 mV). A semifloating electrode was modified from the original floating electrode to be applicable to the in vivo kidney preparation whose pulsatile and respiratory movements had hindered yielding a stable cell PD. This electrode is constructed simply by replacing the shaft of the Ling-Gerard glass microelectrode with a length of flexible silcone-rubber tubing. The cell PD recorded by this electrode is found to be more stable and can withstand minor tissue distortion in mammalian kidney cells in vivo and also in such a contractile tissue as the secretory coil of the eccrine sweat gland.

Animals↗
PubMed2001

Laminated microelectrodes: a simple approach to the construction of inexpensive microelectrodes with a variety of geometries.

Designs for reusable microelectrodes, which are easy to assemble and so do not require special technical skills or services for their construction, are presented. Three types of microelectrodes are fabricated by lamination of metal foil, wire, and wire grids, producing microband, microdisk, and a linear array of microdisk geometries. The electrodes themselves do not need to be polished prior to their use but are observed to be slightly recessed from the surrounding insulating surface. Good agreement is observed between experimental steady-state voltammetric results in nonaqueous solutions and the relevant analytical theory for the voltammetric current.

Journal Article↗
PubMed1992

Measurement of Net Fluxes of Ammonium and Nitrate at the Surface of Barley Roots Using Ion-Selective Microelectrodes : II. Patterns of Uptake Along the Root Axis and Evaluation of the Microelectrode Flux Estimation Technique.

Net fluxes of NH(4) (+) and NO(3) (-) into roots of 7-day-old barley (Hordeum vulgare L. cv Prato) seedlings varied both with position along the root axis and with time. These variations were not consistent between replicate plants; different roots showed unique temporal and spatial patterns of uptake. Axial scans of NH(4) (+) and NO(3) (-) net fluxes were conducted along the apical 7 centimeters of seminal roots of intact barley seedlings in solution culture using ion-selective microelectrodes in the unstirred layer immediately external to the root surface. Theoretically derived relationships between uptake and concentration gradients, combined with experimental observations of the conditions existing in our experimental system, permitted evaluation of the contribution of bulk water flow to ion movement in the unstirred layer, as well as a measure of the spatial resolution of the microelectrode flux estimation technique. Finally, a method was adopted to assess the accuracy of this technique.

Journal Article↗
PubMed1996

Microgalvanics: locally resolved concentration measurements with ion-selective microelectrodes and chronoamperometric microelectrodes.

Localized electrochemical analysis in the micrometer-range is useful for the in situ investigation of galvanic plating processes. Two techniques are presented, a potentiometric and a chronoamperometric one, using xyz-positionable microelectrodes for practical concentration measurements in microstructures during cathodic metal deposition. Locally measured concentration data c(xy) are related to local current density i(xy), which is not obtainable by other means in a system containing excess supporting electrolyte.

Journal Article↗
PubMed1979

Electrochemical properties of Na+- and K+-selective glass microelectrodes.

Electrochemical properties of Na+-selective glass microelectrodes were studied and compared with those of K+-selective glass microelectrodes. The selectivity of Na+-selective glass microelectrodes depended on the ion concentration of test solutions. With aging, resistance of Na+-selective microelectrodes increased and their selectivity for Na over K decreased. Na+-selective microelectrodes potential measured in NaCl solution remained constant with aging, while the potential measured in KCl solution decreased and became more positive. The changes in resistance and potential of Na+-selective microelectrodes may be due to the effects of the less mobile cation, i.e., H+ or K+ on the Na ion exchange in the Na-sensing region. The results indicate that Na+-selective microelectrodes must be used as soon after filling as possible. The selectivity of Na+-selective microelectrodes increased with increase of the sensitive exposed-tip length, whereas their response time became slow due to a large recessed volume, indicating requirement of an optimum exposed-tip length for intracellular applications. The changes in the properties of Na+-selective glass microelectrodes with aging contrasted with those of K+-selective glass microelectrodes in which resistance decreased and K+-selectivity increased. The K+-selective microelectrodes required aging before use for a high selectivity and low resistance. The K+-selective microelectrodes with low resistance after sufficient aging can be used without insulation to measure K+ and Na+ activities in aqueous solutions. The different properties between Na+- and K+-selective microelectrodes are understandable, because hydration of N+-selective glass is much less extensive than that of K+-selective glass.

Electric Conductivity↗
PubMed2000

Comparing cardiac action potentials recorded with metal and glass microelectrodes.

Machine-pulled high-impedance glass capillary microelectrode is standard for transmembrane potential (TMP) recordings. However, it is fragile and difficult to impale, especially in beating myocardial tissues. We hypothesize that a high-impedance pure iridium metal electrode can be used as an alternative to the glass microelectrode for TMP recording. The TMPs were simultaneously recorded from isolated perfused swine right ventricles with a metal microelectrode and a standard glass microelectrode during pacing and during ventricular fibrillation. The basic morphology of TMP recorded with these electrodes was comparable. The action potential duration (APD) at 90% repolarization was 241 +/- 29 ms for the metal microelectrode and 236 +/- 31 ms for the glass microelectrode with a good correlation (r = 0.99, P < 0.0001). The maximum slope value of the APD restitution curves during pacing was also significantly correlated. One metal microelectrode and >20 glass microelectrodes were needed per study. We conclude that, in isolated perfused swine right ventricles, the TMP recorded by the metal microelectrode is comparable with that recorded by the glass microelectrode. Because the metal microelectrode is more durable than the glass microelectrode, it can serve as an alternative for APD recording and for restitution analyses.

Action Potentials↗
PubMed1982

Neutral carrier Na+- and Ca2+-selective microelectrodes for intracellular application.

Na+- and Ca2+-selective microelectrodes were made with Simon's neutral carrier ETH 227 and ETH 1001, respectively, and their properties were studied for intracellular application. The kNaK (selectivity coefficient for Na+ with respect to K+) values of the Na+-selective microelectrodes were in the range of 0.01-0.02, which is comparable to those of recessed-tip Na+-selective glass microelectrodes. The kNaMg values of the microelectrodes were approximately 0.005 so that the interference by intracellular Mg2+ levels could be negligible. The kNaCa values were approximately 2 and the Na+-selective microelectrodes were more selective to Ca2+ than Na+. This indicates that their intracellular application requires special care to handle Ca2+ interference under certain conditions. The kNaK, kNaMg, and kNaCa values did not depend significantly on the methods used for their determination or on the ion activity levels tested. The Nicolsky equation described well the microelectrode potentials in the mixed solutions of NaCl (1-100 mM) and KCl. Potential and resistance of the microelectrodes were stable for a long period and their response time was fast. The results indicate that the Na+-selective microlectrodes are suitable for measurements of intracellular Na ion activities. Ca2+-selective microelectrode potentials at Ca2+ concentrations lower than 10(-4) M changed significantly for the first 2-3 h and then became fairly stable. The rate of the potential change was dependent on the column length of the Ca2+-selective liquid filled. Potentials of the microelectrodes varied from 10-20 mV for Ca2+ between 10(-7) and 10(-6) M concentrations, which may be the cytosolic free-Ca2+ range. With the Ca2+ concentrations greater than 10(-6) M, the microelectrodes had potential changes of approximately 30 mV or greater for a tenfold change in Ca2+ concentration. The kCaK and kCaNa values were in the ranges of 10(-5)-10(-6) and 10(-4)-10(-5), respectively. The kCaMg values were approximately 10(-7). The results show that the Ca2+-selective microelectrodes can be used for measurements of cytosolic Ca ion activities.

Calcium↗
PubMed2000

Pallidotomy microelectrode targeting: neurophysiology-based target refinement.

OBJECTIVE: Microelectrode recording can refine targeting for stereotactic radiofrequency lesioning of the globus pallidus to treat Parkinson's disease. Multiple intraoperative microelectrode recording/stimulating tracks are searched and assessed for neuronal activity, presence of tremor cells, visual responses, and responses to kinesthetic input. These physiological data are then correlated with atlas-based anatomic data to approximate electrode location. On the basis of these physiological properties, one or more tracks are selected for lesioning. This study analyzes the track physiological factors that seem most significant in determining the microelectrode recording track(s) that will be chosen for pallidal lesioning. METHODS: Thirty-six patients with Parkinson's disease underwent microelectrode-guided pallidotomy. Between one and five microelectrode recording tracks were made per patient. Usually, one (n = 23) or two (n = 12) of these tracks were lesioned. Electrode positions in the x (mediolateral) and y (anteroposterior) axes were recorded and related to track neurophysiological findings and final lesion location. The stereotactic location and sequence of microelectrode tracks were recorded and plotted to illustrate individual search patterns. These patterns were then compared with those noted in other patients. Neurophysiological data obtained from recording tracks were analyzed. A retrospective analysis of track electrophysiology was performed to determine the track characteristics that seemed most important in the surgeon's choice of the track to lesion. Track physiological properties included general cell spike amplitude, tremor synchronous neuronal firing, kinesthetically responsive neuronal firing, and optic track responses (either phosphenes reported by the patient during track microstimulation or neuronal firing in response to light stimulus into the patient's eyes). Orthogonally corrected postoperative magnetic resonance images were used to confirm the anatomic lesion locations. RESULTS: In patients who had a single mapped track lesioned, specific track electrophysiological characteristics identified the track that would be lesioned most of the time (20 of 24 patients). Tracks that exhibited a combination of tremor synchronous firing, joint kinesthesia, and visual responsivity were lesioned 17 (85%) of 20 times. Analysis of intraoperative electrode movement in the x and y axes indicated a significant subset of moves but did not result in microelectrode positioning closer to the subsequently lesioned track. Accuracy of initial electrode movement in the x and y axes was most highly correlated with a measure of first-track electrophysiological activity. The number of microelectrode recording tracks did not correlate with clinical outcome. Anatomic analysis, using postoperative magnetic resonance imaging, revealed that all lesions were placed in the globus pallidus. Most patients (35 of 36) improved after surgery. CONCLUSION: The level of electrophysiological activity in the first track was the best predictive factor in determining whether the next microelectrode move would be closer to the ultimately lesioned track. The analysis of electrode track location and neurophysiological properties yields useful information regarding the effectiveness of microelectrode searching in the x and y axes. Within an institution, the application of this modeling method may increase the efficiency of the microelectrode refinement process.

Aged↗
PubMed2005

Electrostatic microactuators for precise positioning of neural microelectrodes.

Microelectrode arrays used for monitoring single and multineuronal action potentials often fail to record from the same population of neurons over a period of time likely due to micromotion of neurons away from the microelectrode, gliosis around the recording site and also brain movement due to behavior. We report here novel electrostatic microactuated microelectrodes that will enable precise repositioning of the microelectrodes within the brain tissue. Electrostatic comb-drive microactuators and associated microelectrodes are fabricated using the SUMMiT V (Sandia's Ultraplanar Multilevel MEMS Technology) process, a five-layer polysilicon micromachining technology of the Sandia National labs, NM. The microfabricated microactuators enable precise bidirectional positioning of the microelectrodes in the brain with accuracy in the order of 1 microm. The microactuators allow for a linear translation of the microelectrodes of up to 5 mm in either direction making it suitable for positioning microelectrodes in deep structures of a rodent brain. The overall translation was reduced to approximately 2 mm after insulation of the microelectrodes with epoxy for monitoring multiunit activity. The microactuators are capable of driving the microelectrodes in the brain tissue with forces in the order of several micro-Newtons. Single unit recordings were obtained from the somatosensory cortex of adult rats in acute experiments demonstrating the feasibility of this technology. Further optimization of the insulation, packaging and interconnect issues will be necessary before this technology can be validated in long-term experiments.

Action Potentials↗