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 55 records · Page 3Linked to original sources
PubMed1983

Methods in laboratory investigation. Identification and evaluation of histopathology at microelectrode puncture sites.

Tissue puncture techniques using microelectrodes for various measurements have been criticized for producing undetermined degrees of tissue damage. Therefore, a method permitting routine identification of puncture tracks was developed to determine local microelectrode-induced injury. Rabbits were anesthetized and the femoral arteries surgically exposed. A 3-ml mixture of saline-India ink suspension was introduced through an ear vein. Oxygen-sensitive (pO2) microcathodes were advanced into and through the arterial wall at 10- or 20-micron intervals using a stepping microdrive to 150 to 450 micron and then withdrawn. The arteries were fixed in 10% formalin and gelatin embedded, and serial frozen sections (less than or equal to 15 micron) of the microelectrode puncture area were made. We observed within 5 minutes of microcathode withdrawal a dark, punctate, microscopic discoloration within the arterial wall. Histologically, ink distribution within the arterial wall demonstrated an acute permeability change: puncture depths generally less than 300 micron showed ink-lined microelectrode tracks (generally less than 2 micron wide) in the media, and greater puncture depths showed local hemorrhage and focal laminar accumulation of ink which extended from the track. The immediate adjacent area to microelectrode puncture depths less than 300 micron showed an apparent intact internal elastic lamina and media. Therefore, microelectrode damage has been shown to be primarily limited to microelectrode tissue tracks.

Animals↗
PubMed1978

A simple circuit for automatic continuous recording of microelectrode resitance.

Microelectrodes with tip diameters less than or equal to 0.5 micron used for intracellular recording sometimes give artefactual readings due to tip potentials. These appear to be caused by a change in the tip of the microelectrode upon impalement with a corresponding change in microelectrode resistance. A circuit is described which enables the resistance of the microelectrode to be continuously monitored throughout an experiment. The electrode is used as one half of a potential divider for an a.c. signal at 20 Hz with an amplitude of 20 mV. The other half of the potential divider is a 1000 Momega resistor. The a.c. signal across the microelectrode is approximately proportional to the microelectrode resistance in the range 0 --50 Momega. This signal is amplified, rectified and smoothed and then displayed on a chart recorder or other convenient meter.

Animals↗
PubMed1998

Comparison of simultaneous pH measurements made with 8-hydroxypyrene-1,3,6-trisulphonic acid (HPTS) and pH-sensitive microelectrodes in snail neurones.

We have evaluated the pyrene-based ratiometric fluorescent dye, 8-hydroxypyrene-1,3,6-trisulphonic acid (HPTS), by using it in conjunction with glass pH-sensitive microelectrodes to measure intracellular pH (pHi) in voltage-clamped snail neurones. Intracellular acidification with propionic acid, and alkalinization following the activation of H+ channels allowed the calibration of the dye to be compared with that of the pH microelectrode over the pH range 6.50-7.50. HPTS calibrated in vitro and glass pH-sensitive microelectrodes produced similar absolute resting pHi values, 7. 16+/-0.05 (n=10) and 7.17+/-0.06 (n=9) respectively in nominally CO2/HCO3--free saline. At both extremes of the pH range there were small discrepancies. At acidic pHi, 6.87+/-0.09 (n=5), the intracellular HPTS measurement differed by -0.08+/-0.03 pH units from the pH-sensitive microelectrode measurement. At alkaline pHi, 7. 32+/-0.10 (n=5), HPTS measurements produced pH values that differed by +0.07+/-0.04 pH units from those of the pH-sensitive microelectrode. Some of the discrepancy could be accounted for by the slow response of the recessed-tip pH-sensitive microelectrode (time constant 77+/-15 s, n=3). Further experiments showed that HPTS, used at an intracellular concentration of 200 microM to 2 mM, did not block activity-dependent pHi changes. The intracellular HPTS concentration was calculated by measurement of intracellular chloride during a series of HPTS-KCl injections. Comparison of HPTS with 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF), at the same concentration, showed that HPTS produces a larger change in ratio over the pH range 6.00-8.00.

Animals↗
PubMed1985

Unit activity, evoked potentials and slow waves in the rat hippocampus and olfactory bulb recorded with a 24-channel microelectrode.

Activity from a number of neighboring neurons can be recorded simultaneously with multichannel microelectrodes. A new version of a 24-channel microelectrode system has been fabricated and used to record different types of neurophysiological data in the rat brain. The system called PRONG (Parallel Recording Of Neural Groups) includes a microelectrode, a lightweight reusable connector, a 24-channel FET-hybrid preamplifier, a 3-band 24-channel amplifier, a 24-channel spike monitor, high-speed digital and analog interfaces and a computer. The electrode-recording locations are arranged in 2 arrays of 12 sites. The arrays are spaced 100 micron apart along either edge of the recording section and the sites within each array are spaced 120 micron apart. The electrodes are fabricated using photolithography in patterned layers totaling 17 micron thick and 114 micron wide in the recording section. The recording sites are 20 micron2 and are plated with platinum black. Performance of the PRONG was compared with that of conventional single microelectrodes and with results in the literature on three kinds of extracellular activity in the rat hippocampal formation and olfactory bulb: action potentials, evoked field potentials and slow-wave activity. The selectivity and sensitivity of the PRONG compared favorably with characteristics of conventional electrodes. Background noise averaged 15 microV and no signal cross talk was observed between neighboring channels. Discriminable action potentials (signal-to-noise ratios of 2:1 to 15:1) were observed at 37-95% of the viable recording sites with a maximum of 19 units in one recording. Units were observed in waking animals for up to 4 days. The waveforms, firing repertoires and laminar distribution of units were the same as those recorded with conventional microelectrodes. This indicates that penetration by the PRONG spares tissue from functional damage. "Instant" laminar profiles were created for commissural and perforant path evoked potentials in the hippocampal formation. These profiles were nearly identical with those created by successive recordings made with conventional microelectrodes. Laminar profiles and behavioral activity appeared to be "normal" as collected with this electrode. These results set the foundation for use of the PRONG as a tool for the study of local neural interactions.

Animals↗
PubMed2004

Sonochemically fabricated microelectrode arrays for biosensors--part II. Modification with a polysiloxane coating.

A polymer-modified sonochemically fabricated glucose oxidase microelectrode array with microelectrode population densities of up to 2.5 x 10(5) microelectrodes per square centimetres is reported. These microelectrode sensors were formed by first depositing an insulating film on commercial screen printed electrodes which was subsequently sonicated to form cavities of regular sizes in the film. Electropolymerisation of aniline at the microelectrode cavities formed polyaniline protrusions containing entrapped glucose oxidase. Chemical deposition of polysiloxane from dichlorodimethysilane was used to deposit a thin protective and diffusion mass transport controlling coating over the electrodes. The physical and electrochemical properties of these films were studied. The performance of the final glucose oxidase based microelectrode sensor array is reported.

Biosensing Techniques↗
PubMed1986

Intracellular microelectrode measurements in small cells evaluated with the patch clamp technique.

Microelectrode penetration of small cells leads to a sustained depolarization of the resting membrane potential due to a transmembrane shunt resistance (Rs) introduced by the microelectrode. This has led to underestimation of the resting membrane potential of various cell types. However, measurement of the fast potential transient occurring within the first few milliseconds after microelectrode penetration can provide information about pre-impalement membrane electrophysiological properties. We have analyzed an equivalent circuit of a microelectrode measurement to establish the conditions under which the peak of the impalement transients (Ep) approaches the pre-impalement resting membrane potential (Em) of small cells most closely. The simulation studies showed that this is the case when the capacitance of the microelectrode is low and the membrane capacitance of the cell high. In experiments performed to assess the reliability of Ep as a measure of Em, whole-cell patch clamp measurements were performed in the current clamp mode to monitor, free from the effects of Rs, Em in cultured human monocytes. Microelectrode impalement of such patch clamped cells and measurement of Ep made it possible to detect correlation between Ep and Em and showed that for small cells such as human monocytes Ep is on average 6 mV less negative than the resting membrane potential.

Cell Membrane↗
PubMed2002

Improved ceramic-based multisite microelectrode for rapid measurements of L-glutamate in the CNS.

This paper describes improvements and further characterization of a ceramic-based multisite microelectrode for in vivo measurements of L-glutamate. Improvements include increased recording area, insulation deposition using photolithography for more uniform recording sites and forming the microelectrodes using a diamond saw providing smoother microelectrode edges. The new microelectrodes are triangular in shape, 1 cm in length and taper from 1 mm to a 2-5 microm tip. Details on performing in vivo measurements are given, including microelectrode preparation, pitfalls of the recording method and approaches to enhance reproducibility of the technique. The detection limit for L-glutamate was lowered to approximately 0.5 microM and a self-referencing recording technique was utilized to remove interferents as well as decrease noise. Applications of the microelectrodes to study L-glutamate uptake and release in rat prefrontal cortex, cortex, cerebellum and striatum are included.

Animals↗
PubMed2000

B-mode and color Doppler ultrasound imaging for localization of microelectrode in monkey brain.

Using alert monkeys, we attempted ultrasound imaging after partial craniotomy to localize a metal microelectrode in the brain. B-mode ultrasonography provided images of sulcus and gyrus patterns of the cerebral cortex, and locations of the ventricles and subarachnoid cisterns. As the microelectrode proceeded in the brain, the position of the microelectrode was clearly identified. Electrolytic microlesions generated by delivering direct currents via the microelectrode could also be detected. Color Doppler imaging of blood vessels of the brain was helpful to demarcate deep brain structures and to avoid accidental injury of the blood vessels by the microelectrode. The ultrasonography will make it possible to place recording microelectrodes or injection needles accurately in target regions of the brain in physiological, anatomical or behavioral experiments.

Animals↗
PubMed2005

An efficient cell separation system using 3D-asymmetric microelectrodes.

An efficient 3D-asymmetric microelectrode system for high-throughput was designed and fabricated to enhance sorting sensitivities to the dielectric properties-size, morphology, conductivity, and permittivity-of living cells. The principle of the present system is based on the use of the relative strengths of negative dielectrophoretic and drag forces, as in a conventional 3D-microelectrode system. Whereas the typical 3D-microelectrode system has a constant electric field magnitude due to the constant width of the microelectrodes and a fixed gap between face-to-face microelectrodes, the present 3D-asymmetric microelectrode system has electric fields of continuously varying magnitudes along the transverse direction of a channel owing to the changing widths of the electrodes in the half-circular shaped cross section of the microchannel. Thus, varying dielectric forces are generated, leading to increased sorting sensitivity through differentially induced forces to definitely distinct cell types. Numerical analysis verified the improved sensitivity of the present system for sorting living cells. The feasibility of using the newly fabricated system under experimental conditions was tested by demonstrating that a mixed population of mouse P19 embryonic carcinoma (EC) and red blood cells (RBCs) was effectively sorted to different wells depending on their respective relative physical properties.

Animals↗
PubMed2002

Microelectrode technique for in situ measurement of carbon dioxide concentrations in xylem sap of trees.

We developed a new microelectrode technique for measuring CO2 concentration ([CO2]) in xylem sap of trees. This technique enabled us to make rapid and continuous measurements of xylem sap [CO2] in situ. In this report, we discuss the methodology and establish the feasibility of the technique. We also describe calibration procedures, temperature sensitivity, field use and other characteristics of the microelectrodes. An example of data collected in the field is provided. Microelectrode calibration was accomplished at constant temperature in air of known [CO2]. When sampling temperature differed from calibration temperature, correction was necessary. We developed an equation to correct for temperatures between 15 and 35 degrees C when calibration was conducted at 25 degrees C. Equations based on Henry's Law were used to convert measured gas phase [CO2] (%) to concentration of all products of CO2 dissolved in sap (mmol l(-1)). We inserted microelectrodes into stems of three tree species to measure diurnal changes in [CO2] in the xylem sap. A diurnal pattern with depression during the day and elevation at night was observed. Mean daily [CO2] ranged from 1.6 to 10.3 mmol l(-1). Microelectrodes were suitable for making diurnal measurements for up to 7 days without recalibration. We also used the microelectrodes to measure [CO2] of soil in situ. Soil [CO2] ranged from 1 to 4% (gas phase), with little diurnal variation.

Calibration↗
PubMed2001

Finite element analysis of the current-density and electric field generated by metal microelectrodes.

Electrical stimulation via implanted microelectrodes permits excitation of small, highly localized populations of neurons, and allows access to features of neuronal organization that are not accessible with larger electrodes implanted on the surface of the brain or spinal cord. As a result there are a wide range of potential applications for the use of microelectrodes in neural engineering. However, little is known about the current-density and electric field generated by microelectrodes. The objectives of this project were to answer three fundamental questions regarding electrical stimulation with metal microelectrodes using geometrically and electrically accurate finite elements models. First, what is the spatial distribution of the current density over the surface of the electrode? Second, how do alterations in the electrode geometry effect neural excitation? Third, under what conditions can an electrode of finite size be modeled as a point source? Analysis of the models showed that the current density was concentrated at the tip of the microelectrode and at the electrode-insulation interface. Changing the surface area of the electrode, radius of curvature of the electrode tip, or applying a resistive coating to the electrode surface altered the current-density distribution on the surface of the electrode. Changes in the electrode geometry had little effect on neural excitation patterns, and modeling the electric field generated by sharply tipped microelectrodes using a theoretical point source was valid for distances > approximately 50 microm from the electrode tip. The results of this study suggest that a nearly uniform current-density distribution along the surface of the electrode can be achieved using a relatively large surface area electrode (500-1000 microm2), with a relatively blunt tip (3-6 microm radius of curvature), in combination with a thin (approximately 1 microm) moderately resistive coating (approximately 50 omega m).

Biocompatible Materials↗
PubMed1987

Cl(-)-selective microelectrodes: sensitivity to anionic Cl- transport inhibitors.

Cl(-)-selective microelectrodes, containing Corning code 477315 or 477913 liquid ion exchangers, are often used to measure extra- and intracellular Cl- activities in the presence of Cl- transport inhibitors such as furosemide, bumetanide, and the stilbene sulfonic acid derivative 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Because these inhibitors are anions in the physiological pH range and have relatively high lipid solubilities, they would be expected to interfere with the response to Cl- of these microelectrodes. Preliminary reports have confirmed this expectation. We examined the effect of furosemide, bumetanide, and SITS on the Cl(-)-selective barrels of double-barreled microelectrodes containing Corning code 477315 liquid anion exchanger and suitable for impaling small cells (e.g., epithelial cells). The results showed that at pH 8.2 in pure solutions of furosemide and bumetanide, these microelectrodes gave linear responses to the logarithm of furosemide or bumetanide concentrations ranging from 1 X 10(-2) to 1 X 10(-4) M. In the physiological pH range both these inhibitors (in concentrations of 0.1 mM) interfered significantly with the response of the microelectrodes to Cl- (in concentrations ranging from 100 to 1 mM). Calculated electrode sensitivities, relative to Cl-, were approximately 150 for both these compounds. Microelectrodes of this type appeared to be approximately 1,000 times as sensitive toward SITS as they were toward Cl-.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1994

Disruptive effects of protein on performance of liquid membrane-based ion-selective microelectrodes.

The effects of addition of protein [bovine serum albumin (BSA)] to the calibration solutions of various liquid membrane-based ion-selective microelectrodes have been assessed. Protein at typically cytosolic levels of 100 mg/ml had no effect on the response of Na(+)-, K(+)-, Mg(2+)-, Ca(2+)-, H(+)-, NO3(-)-, and Cl(-)- selective microelectrodes at ion concentrations well above the respective detection limits. By contrast, this level of protein resulted in a pronounced increase in the detection limits of Na(+)-, K(+)-, Mg(2+)-, Ca2+, and Cl(-)-selective microelectrodes; H+ and NO3- microelectrodes were largely unaffected by the protein. The effect of BSA on detection limit is independent of pH and ionic strength, nor is it due to hysteresis, to binding of ions to the protein, or to the generation of junction potentials. More extensive studies on Na(+)-selective microelectrodes revealed that other proteins and large molecules (e.g., polyethylene glycol) also increase detection limits, with the extent of this effect apparently correlated positively with the molecular weight. Because biological macromolecules at physiological concentrations can influence the properties of alkali- and alkali earth cation-selective microelectrodes, care must be taken if the use of these electrodes entails cytosolic measurements close to their detection limits.

Equipment Failure↗
PubMed1981

Ionic activities in cardiac muscle cells and application of ion-selective microelectrodes.

Intracellular activities of K, Na, H, Cl, and Ca ions are kept at an optimal level for maintenance of normal cellular functions. Furthermore, many cellular functions are regulated directly or indirectly by these ion activities in cells. The use of ion-selective microelectrodes has emerged as the only method for measuring directly and continuously intracellular ion activities of intact cells. In recent years, they have been extensively used for measurements of intracellular ion activities in cardiac muscle and other tissues. This article concerns both intracellular ion activities of cardiac muscle and intracellular application of ion-selective microelectrodes. Intracellular ion activities in cardiac muscle cells have been measured under several experimental conditions, such as changes in ion composition of bathing fluid and exposure to certain drugs. This approach has provided significant information about electrochemical potentials of ions, membrane transport, and cellular functions related to ion activities. Relevant data and information is presented for K+, Na+, H+, Cl-, and Ca2+. Although ion-selective microelectrodes are widely used, this technique has certain assumptions, problems, and limitations that vary with the types of microelectrodes. The appendix of this article reviews basic principles for intracellular application of ion-selective microelectrodes and examines pertinent assumptions, problems, and issues. Particular features of K+-, Na+-, H+-, Cl--, and Ca2+-selective microelectrodes are described.

Animals↗
PubMed2005

Ion-selective microelectrode analysis of salicylate transport by the Malpighian tubules and gut of Drosophila melanogaster.

Transport of the organic anion salicylate by the Malpighian tubules and gut of larval and adult fruit flies was studied using two salicylate-selective microelectrode methods. The first method combined the high selectivity of tridodecylmethylammonium-based electrodes for salicylate with the self-referencing ion-selective microelectrode technique for non-invasive spatial and temporal analysis of salicylate flux. Measurements with this technique revealed secretion of salicylate across the main and distal segments of the Malpighian tubule as well as the midgut, ileum and rectum. The second method used a salicylate-selective microelectrode to measure the concentration of salicylate in fluid droplets secreted by isolated Drosophila Malpighian tubules set up in a Ramsay secretion assay. Transepithelial salicylate flux was calculated as the product of fluid secretion rate and secreted fluid salicylate concentration. Measurements with this method revealed that salicylate transport was active and saturable; the kinetic parameters J(max) and K(t) were 2.72 pmol min(-1) tubule(-1) and 0.046 mmol l(-1), respectively. Measurements of transepithelial salicylate flux determined by both microelectrode methods were in good agreement. Transepithelial flux measurements measured by microelectrodes were also validated by comparing them with measurements of radiolabelled salicylate levels in secreted droplets. Salicylate concentrations in haemolymph samples were measured with salicylate-selective microelectrodes after injection of salicylate into the haemocoel or after insects were fed salicylate-rich diets. The rate of salicylate secretion by Malpighian tubules in vitro was sufficient to account for the measured rate of decline of salicylate concentration in the haemolymph in vivo.

Analysis of Variance↗
PubMed1976

Physicochemical properties of a liquid ion exchanger microelectrode and its application to biological fluids.

Double-barreled potassium or chloride ion-selective microelectrodes were constructed using a liquid ion exchanger. Technical details of the fabrication of double-barreled microelectrodes, having a PD sensor as one barrel and an ionic sensor as the other, are described. The sensitivity of K+ or CI- ion-selective microelectrodes exhibited an approximately Nernstian response over a temperature range of 7 degrees-37 degrees C, and the electromotive force (EMF) was stable within +/- mV for a few hours. The rise time was less than 1 sec. The effect of pH on the electrode response was negligible over a physiological range of pH 5.6 to 7.8. The selectivity constants of the K+ microelectrode to other cations were 0.011 for Na+, 0.200 for NH+4, and less than 0.002 and 0.001 for Ca++ and Mg++, respectively, while that of the CI- microelectrode was 0.067 for HCO-3. Glucose or urea has no effect on the EMF. Protein has a significant effect on ion exchanger membrane only when the concentration of the tested ion is low and protein is high. On the basis of this background the determination of K+ and CI- activity was carried out both in vivo and in vitro on several biological samples, such as serum, tissue and cellular fluids, and other protein-containing fluids. The values obtained with the microelectrode were consistent with those obtained with the other conventional methods or with the current theory on electrolyte solutions. These results were taken to assure the practical application of these electrodes to biological studies in many fields.

Animals↗
PubMed1980

Physicochemical characteristics of antimony microelectrode with special reference to selection of standard buffers.

1) Antimony (Sb) microelectrodes with tips of 2 to 5 micrometers in outside diameter were constructed, and their electromotive forces (EMF) were tested in response to the pH of several calibration buffers. The data were compared with those of glass pH electrodes. 2) Increasing ionic strength (I) caused a significant deviation in pH readings of the Sb-microelectrode (delta pHSb-Glass). The above salt effect was empirically given by delta pHSb-Glass = 0.017--0.125 I (I = 0.09--0.22) 3) Even with the correction for ionic strength, the values of delta pHSb-Glass were still dependent on the nature of calibration buffers employed. Among various buffers, Tris buffer [Tris(hydroxymethyl)-aminomethane, (THAM)] had the least disturbance on the Sb-microelectrode, and bicarbonate had also relatively minor effect. 4) The pH value according to the Sb-electrode was caused to deviate considerably by phosphate. The effect of phosphate within the range of 1 to 67 mM can be predicted by 1/delta pHSb-Glass = 1 + (0.174/[PO4]) 5) Like phosphates, BES [N, N-Bis (2-hydroxyethyl)-2-aminoethane sulfonic acid] also had a significant effect on the EMF of the Sb-microelectrode. 6) Upon consideration of the above facts, measurements of several biological fluids, such as those of the in vivo pH of intratubular fluid of bullfrog kidney were carried out with the Sb-microelectrode calibrated by 90 mM Tris buffer. 7) Thus, it was concluded that the Sb-microelectrode when properly calibrated could be used for the pH measurement of ultraminute amounts of biological samples.

Animals↗
PubMed1980

Temperature coefficient of and oxygen effect on the antimony microelectrode.

With regard to pH measurement of biological fluids in vivo with metal-metal oxide microelectrodes, the effect of temperature and partial pressure of oxygen on antimony (Sb) microelectrodes was examined, and pH of blood was estimated in the bullfrog. The temperature coefficient (dE/dt) of electromotive force (EMF) of Sb-microelectrodes in the range of 7 to 37 degrees C was -1.18 +/- 0.113 mV/degrees C (mean +/- SEM) in Ringer solution, whereas that of the pH glass electrode in the same solution was -0.43 +/- 0.035 mV/degrees C. When estimated in Tris buffer solution, it was -0.06 +/- 0.063 mV/degrees C for Sb-microelectrodes and 1.05 + 0.036 mV/degrees C for glass electrodes. The change of slope constant (alpha in -mV/pH) in the Sb-microelectrode due to temperature change could be predicted empirically from: alpha = 0.40 (t-25) + 55.3, where t represents the measuring temperature in degrees C. The resultant deviation of pH reading between Sb and glass electrodes, delta pHSb-Glass, may be expressed by: delta pHSb-Glass = 0.00183 (t-25) +0.016. In the range of 45 to 760 mmHg of oxygen partial pressure it fixed pH, the EMF increased linearly with the increase of Po2, the slope (dE/dlog(Po2)) being 11.7 +/- 0.42 (SEM) mV (n = 13, t = 25 degrees C). In consideration of the above effects, the blood pH of bullfrog was estimated to be 7.697 +/- 0.092 (SD) and 7.729 +/- 0.111 with glass and Sb-microelectrodes respectively, the difference between the two being relatively minor.

Animals↗