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PubMed2006

Dielectrophoresis of DNA: time- and frequency-dependent collections on microelectrodes.

This paper reports measurements that characterize the collection of DNA onto interdigitated microelectrodes by high-frequency dielectrophoresis. Measurements of time-dependent collection of 12 kilobase pair plasmid DNA onto microelectrodes by dielectrophoresis show significant reduction in the response as the frequency increases from 100 kHz to 20 MHz. Collection time profiles are quantitatively measured using fluorescence microscopy over the range 100 kHz to 5 MHz and are represented in terms of two parameters: the initial dielectrophoretic collection rate, and the initial to steady-state collection transition. Measured values for both parameters are consistent with trends in the frequency-dependent real part of the effective polarizability measured for the same plasmid DNA using dielectric spectroscopy. The experimentally measured parameters are qualitatively compared with trends predicted by theory that takes into account dielectrophoretic particle movement and diffusion. The differences between experiment and theory are discussed with suggested improvements to theoretical models, for example, including the effects of electrohydrodynamically driven fluid motion.

Coated Materials, Biocompatible↗
PubMedDate not supplied

Estimation of intracellular free magnesium using ion-selective microelectrodes: evidence for an Na/Mg exchange mechanism in skeletal muscle.

Mg-selective microelectrodes allow continuous direct recording of intracellular free magnesium concentration ([Mg]i). Mg-selective microelectrodes utilizing the neutral carrier ETH 1117 have been used to determine [Mg]i in a wide variety of tissues. However, this type of electrode suffers from considerable interference from other cations (primarily potassium and sodium when used for intracellular studies). The recently developed Mg sensor ETH 5214 reveals a much improved selectivity and sensitivity as compared to ETH 1117. For intracellular measurements of [Mg]i the interference from Na+, K+, Ca2+ and pH can be neglected. Measurements of resting [Mg]i in ferret ventricular muscle and frog skeletal muscle gave values of 0.85 and 0.93 mM, respectively. These values indicate that [Mg]i is not in a thermodynamic equilibrium and Mg2+ ions have to be extruded continuously from the cytoplasm against their electrochemical gradient. In skeletal muscle, measurements of [Mg]i and [Na]i under experimental conditions, which included changes of the membrane potential and the transmembrane gradients for Mg2+ and Na+, provided evidence that an Na/Mg exchange mechanism participates in maintaining [Mg]i at low cytoplasmic levels.

Animals↗
PubMed1991

Dose-dependent thermal response of tumor pH and energy metabolism evaluated by in vivo 31P NMR spectroscopy and microelectrodes.

In vivo 31P NMR spectroscopy and pH microelectrodes were employed to measure the energy metabolism and pH of a mammary carcinoma in the flank of the C3H mouse before and serially up to a week after various hyperthermia treatments. Water bath hyperthermia was used to treat the tumor at 43.5 degrees C for 30 min (TCD0/30, NMR measurement only), 1 h (TCD10/30), and 2 h (TCD60/30), respectively. The data indicate that, except at 4 h after TCD60/30 treatment, all pH values measured by NMR (pHn) were significantly higher (P less than or equal to 0.001) compared to pH values measured by microelectrodes (pHe) at all treatment levels and times. The magnitude of the difference between pHn and pHe (delta pH) was significantly decreased from the pretreatment level only at 4 h after hyperthermia treatment (0.51 pH units for TCD60/30 and 0.21 pH units for TCD10/30). The ratio of beta-nucleoside triphosphate to inorganic phosphate (beta-NTP/Pi) and pHn were more sensitive to hyperthermia treatment than pHe. The beta-NTP/Pi ratio failed to recover to the pretreatment ratio after 1 or 2 h hyperthermia treatment, while a total recovery was observed within 72 h for 30 min hyperthermia treatment. Our data suggest that the temporal profile of beta-NTP/Pi, pHn, and delta pH may be indicative of the biological outcome of hyperthermia treatment.

Animals↗
PubMed1988

Estimation of the upper limit of the free magnesium concentration measured with Mg-sensitive microelectrodes in ferret ventricular muscle: (1) use of the Nicolsky-Eisenman equation and (2) in calibrating solutions of the appropriate concentration.

Determination of intracellular free magnesium [( Mg]i) with ion-selective Mg microelectrodes filled with the neutral carrier ETH 1117 is critically dependent on the values taken for K and Na in the calibrating solutions, for intracellularly the Mg microelectrodes also respond to these ions. This study was designed to test the influence of K and Na on the measured [Mg]i in ferret ventricular muscle. To estimate the effect of these ions, two methods were used: calculation based on the Nicolsky-Eisenman equation and calibration of the electrodes in solutions containing various concentrations of K and Na. Selectivity coefficients were measured for K and Na by the fixed interference method. While the Nicolsky-Eisenman equation could describe the behavior of an electrode in a given calibrating solution, the effects of changes in either the concentration of K and/or Na could not be predicted by the equation. Comparison between calibrating solutions containing the mean values for K and Na and calibrating solutions containing the lowest measured values for K and Na showed that the mean [Mg]i in ferret ventricle would increase from 0.4 to 0.9 mmol/l. A critical appraisal of the literature values for [Mg]i in muscle tissue suggests that values over 2 mmol/l were either unphysiological or too high for methodological reasons.

Animals↗
PubMed1982

[Determination of dissociation exponent of CO2 used in Henderson-Hasselbalch equation by means of bicarbonate-selective microelectrode].

To measure intracellular ion activity of bicarbonate directly, a double-barreled bicarbonate-selective microelectrode was constructed with a liquid ion exchanger(LIX) containing tri-n-octylammonium, trifluoroacetyl-butyl benzene and octanol. A new dissociation exponent of CO2 (pK') was determined experimentally for a modified Henderson-Hasselbalch equation, in which HCO3 activity was used instead of HCO3 concentration. The temperature effects on pK' and solubility coefficient of CO2 were analyzed over the range of 10 to 40 degrees C. The average values of pK' at room temperature (22 degrees C) were 6.377 and 6.348 in water and frog serum, respectively, and the solubility coefficients of CO2 were 0.048 and 0.046 mM/L/mmHg. The values of pK' plotted on Arrhenius plot were shown linear with 1/T, indicating that the pK' thus obtained can be treated thermodynamically as a first-order kinetics. Under normal circumstances, the values for the intracellular pH predicted from the intracellular bicarbonate activities in the proximal tubule and sartorius muscle of bullfrogs were virtually identical with those obtained directly by the LIX-pH-microelectrodes.

Animals↗
PubMed1997

Exploring the human brain using single-unit microelectrode technique during awake stereotactic functional neurosurgery.

In neuroscience research, the use of true single-unit microelectrode technique has been confined largely to the animal neurophysiology laboratory due to the complexity of the equipment required and the fastidious, time-consuming nature of the methodology. We report here our successful clinical use of this technique in human patients with Parkinson's disease undergoing awake stereotactic movement disorder neurosurgery. The common targets in such operations are the postero-ventral portion of the globus pallidus interna in the basal ganglia (for dopa-induced dyskinesias particularly) and the ventro-intermediate nucleus of the thalamus (for tremor-predominant Parkinson's disease). Accurate and exquisite neurophysiological localisation of these small targets deep within the brain can be obtained with single-unit microelectrode technique prior to the insertion of a deep brain stimulator or definitive neurosurgical radiofrequency lesioning in the target area. This accuracy translates into better outcomes for patients and a reduced incidence of complications. The wealth of data gained from studying the abnormal behaviour of neurons within the basal ganglia and thalamus also provides us with fundamental insights into the pathophysiology behind Parkinson's disease.

Basal Ganglia↗
PubMed1986

Microelectrode maps, myeloarchitecture, and cortical connections of three somatotopically organized representations of the body surface in the parietal cortex of squirrels.

Microelectrode mapping methods and anatomical procedures were combined in the same animals to reveal the cortical connections of three architectonically distinct representations of the body surface in the somatosensory cortex of grey squirrels. In individual experiments, microelectrode multiunit recordings were used to determine the somatotopic organization of regions of the cortex and to identify sites for injections of the anatomical tracer, wheat germ agglutinin conjugated to horseradish peroxidase. After the brains were perfused, the cortex was separated from the brainstem, flattened, and cut parallel to the flattened surface to facilitate comparisons of areal connection patterns, physiological data, and architectonic subdivisions. Recordings in the primary (S-I) and secondary (S-II) somatosensory fields confirmed earlier descriptions of the somatotopic organization of these fields (Sur et al.: J. Comp. Neurol. 179:425-450, '78; Nelson et al.: J. Comp. Neurol. 184:473-490, '79). In addition, recordings in the cortex caudal to S-I and ventral to S-II revealed a third representation of the body surface in parietal cortex, the parietal ventral area (PV). Neurons in PV were responsive to light tactile stimulation of skin and hairs. Multiple unit receptive fields of neurons in PV were larger than those for neurons in S-I but similar in size to those for neurons in S-II. PV represented the contralateral body surface in a somatotopic manner that can be roughly characterized as an inverted "homunculus" with the limbs directed medially, the trunk located ventrally, and the face congruent with the representations of the upper lip and nose in S-I. Neurons in some electrode penetrations in PV were also responsive to auditory clicks. Microlesions placed at physiologically determined borders allowed all three somatic representations to be related to myeloarchitectonically defined fields. S-I was architectonically distinct as a densely myelinated region. Within S-I, a lightly myelinated oval of the cortex between the representation of the hand and face, the "unresponsive zone" (Sur et al.: J. Comp. Neurol. 179:425-450, '78), was an easily recognized landmark. S-II and PV corresponded to less densely myelinated fields. Other subdivisions such as motor cortex, primary auditory cortex, and visual areas 17 and 18 were distinguished. Connections were revealed by placing injections within S-I, S-II, or PV.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1968

Microelectrode studies of dog's gastric mucosa.

In anesthetized dogs, the potentials in the mucous coat and gastic cells were measured with microelectrodes. In the secreting stomach, with isotonic saline in contact with the mucosal surface, the orientation of the initial change in potential difference (PD) was often the same as that of the liquid junction potential between gastric juice and saline (the microelectrode became negative to a reference electrode in the saline) but the magnitude of the change was never more than 11 mv. On the basis of this finding an explanation is offered for the observation that in the secreting stomach replacing isotonic saline with isotonic HCl as the bathing fluid on the mucosal surface, results in a change in the serosal to mucosal PD of only 19 mv, which is 40% less than the liquid junction potential between gastric juice and saline. In the surface epithelial cells of both resting and secreting stomach, multiple levels of potentials were found. For the secreting stomach, the resistance between the interstitial fluid of the pit region and the fluid on the mucosal surface was 55 ohm cm(2), determined as the change in PD per unit of applied current across stomach. The implications of these findings are discussed with reference to the separate site theory of HCl formation.

Animals↗
PubMed1983

Comparison of tubal surgery with the CO2 laser and the unipolar microelectrode.

The uterine horns of 40 New Zealand White female rabbits were resected and anastomosed to compare microsurgical anastomosis of the horns excised with microscissors, with a laser, and with a microelectrode. The rabbits were divided into four groups. In the first group of ten rabbits, 3 cm of tissue was resected by microscissors from each uterine horn; the cut ends were then anastomosed in one layer with 8-0 Vicryl sutures using the operating microscope. In the second group of ten rabbits, 3 cm of tissue was resected by laser from each uterine horn; the cut ends were then anastomosed in one layer with 8-0 Vicryl. In the third group of ten rabbits, 3 cm of tissue was resected by laser from each uterine horn; the cut ends were then anastomosed by "welding" the tissues with the laser. In the fourth group of ten rabbits, 3 cm of tissue was resected by a microelectrode; the cut ends were then anastomosed in one layer with 8-0 Vicryl sutures using loupe magnification. All the rabbits in the first and fourth groups became pregnant, only four became pregnant in the second group, and none became pregnant in the third group. It is concluded that the CO2 laser beam as used in this study has no place in tubal resection and reconstruction.

Animals↗
PubMed1997

Determination of cysteine by capillary zone electrophoresis with end-column amperometric detection at a gold/mercury amalgam microelectrode without deoxygenation.

Capillary zone electrophoresis was employed for the determination of cysteine using an end-column amperometric detection with a gold/mercury amalgam microelectrode, at a constant potential of 0.02-0.06 V vs. saturated calomel electrode. In this procedure deoxygenation is not necessary. The electrochemical characteristics at the microelectrode, the effect of the concentration of the buffer and the separation voltage across the capillary on the migration time and separation efficiency, and the dependence of the injection voltage and time on the detection signal, the separation efficiency and coulometric efficiency has been investigated. The calibration plot was found to be linear over four orders of magnitude and the limit of detection was 5.8 x 10(-8) mol/l (or 14.5 amol). The method was applied to the determination of cysteine in human plasma, blood and urine.

Buffers↗
PubMed2003

Evaluation of the impact of bioaugmentation and biostimulation by in situ hybridization and microelectrode.

Three rotating disk biofilm reactors were operated to evaluate whether bioaugmentation and biostimulation can be used to improve the start-up of microbial nitrification. The first reactor was bioaugmented during start-up period with an enrichment culture of nitrifying bacteria, the second reactor received a synthetic medium containing NH(4)(+) and NO(2)(-) to facilitate concomitant proliferation of ammonia- and nitrite-oxidizing bacteria, and the third reactor was used as a control. To evaluate the effectiveness of bioaugmentation and biostimulation approaches, time-dependent developments of nitrifying bacterial community and in situ nitrifying activity in biofilms were monitored by fluorescence in situ hybridization (FISH) technique and microelectrode measurements of NH(4)(+), NO(2)(-), NO(3)(-), and O(2). In situ hybridization results revealed that addition of the enrichment culture of nitrifying bacteria significantly facilitated development of dense nitrifying bacterial populations in the biofilm shortly after, which led to a rapid start-up and enhancement of in situ nitrification activity. The inoculated bacteria could proliferate and/or survive in the biofilm. In addition, the addition of nitrifying bacteria increased the abundance of nitrifying bacteria in the surface of the biofilm, resulting in the higher nitrification rate. On the other hand, the addition of 2.1mM NO(2)(-) did not stimulate the growth of nitrite-oxidizing bacteria and did inhibit the proliferation of ammonia-oxidizing bacteria instead. Thus, the start-up of NO(2)(-) oxidation was unchanged, and the start-up of NH(4)(+) oxidation was delayed. In all the three biofilm reactors, data sets of time series analyses on population dynamics of nitrifying bacteria determined by FISH, in situ nitrifying activities determined by microelectrode measurements, and the reactor performances revealed an approximate agreement between the appearance of nitrifying bacteria and the initiation of nitrification activity, suggesting that the combination of these techniques was a very powerful monitoring tool to evaluate the effectiveness of bioaugmentation and biostimulation strategies.

Biofilms↗
PubMed2002

An electrochemical redox couple activitated by microelectrodes for confined chemical patterning of surfaces.

Microelectrodes, printed as an array on the surface of a silicon chip, generate chemically active species in a solution of electrolyte held between the electrode array and a glass plate. The active species induce chemical change in molecules coupled to the surface of the glass plate, which is separated from the electrode array by a gap of several micrometers. This paper explores the nature and pattern of the induced chemical change. The patterning is discussed with respect to the electrolyte composition and the magnitude and duration of current applied to the microelectrodes. We show that under suitable conditions the active species is confined to micrometer-sized features and diffusion does not obscure the surface pattern produced.

Journal Article↗
PubMed2003

Application of diamond microelectrodes for end-column electrochemical detection in capillary electrophoresis.

Highly boron-doped diamond microelectrodes were employed in an end-column electrochemical detector for capillary electrophoresis (CE). The diamond microline electrodes were fabricated from conducting diamond thin films (exposed surface area, 300 x 50 microm), and their analytical performance as CE detectors was evaluated in a laboratory-made CE installation. The CE-ED system exhibited high separation efficiency for the detection of several catecholamines, including dopamine (DA), norepinephrine (NE), and epinephrine (E), with excellent analytical performance, for example, 155,000 theoretical plates for DA. The diamond-based electrochemical detection system also displayed low detection limits (approximately 20 nM for E at S/N = 3) and a highly reproducible current response with 10 repetitive injections of mixed analytes containing DA, NE, and E (each 50 microM), with relative standard deviations (RSD) of approximately 5%. The performance of the diamond detector in CE was also evaluated in the detection of chlorinated phenols (CP). When compared to the carbon fiber microelectrode, the diamond electrode exhibited lower detection limits in an end-column CE detection resulting from very low noise levels and highly reproducible analyses without electrode polishing due to analyte fouling, which makes it possible to perform easier and more stable CE analysis.

Journal Article↗
PubMed2003

Carbon nanotube fiber microelectrodes.

Carbon nanotube (CNT) fibers have been used to fabricate microelectrodes with an attractive electrochemical behavior. By combining the advantages of CNT materials and fiber microelectrodes, the new material expands the scope of CNT-based electrochemical devices. The CNT fiber offers a marked decrease in the overvoltage for the NADH, dopamine, and hydrogen peroxide and circumvents NADH surface fouling effects. Heat treatment is shown to be extremely useful for activating the CNT fiber surfaces for electron transfer. SEM imaging and cyclic-voltammetric data indicate that the heat treatment leads to the removal of nonconducting residues and exposure of a "fresh" CNT surface. The new electrode material thus presents new opportunities for a wide range of electrochemical and analytical applications.

Journal Article↗
PubMed2006

Building addressable libraries: The use of a mass spectrometry cleavable linker for monitoring reactions on a microelectrode array.

Time-of-flight secondary ion mass spectrometry (TOF SIMS) has been used in conjunction with a mass spectrometry cleavable linker to determine the percent conversion of reactions that were conducted site-selectively on an addressable microelectrode array. When combined with fluorescence techniques for analysis of the reactions, the TOF SIMS experiment provides a means for optimization of both reaction confinement and reaction efficiency on the microelectrode arrays.

Calibration↗
PubMed2000

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements

Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the charge relaxation frequency of the electrolyte. The velocity of latex tracer particles was measured as a function of applied signal frequency and potential, electrolyte conductivity, and position on the electrode surface. The data are discussed in terms of a linear model of ac electroosmosis: the interaction of the nonuniform ac field and the induced electrical double layer.

Journal Article↗
PubMed1998

Development, Characterization, and Application of a Cadmium-Selective Microelectrode for the Measurement of Cadmium Fluxes in Roots of Thlaspi Species and Wheat

A Cd2+-selective vibrating microelectrode was constructed using a neutral carrier-based Cd ionophore to investigate ion-transport processes along the roots of wheat (Triticum aestivum L.) and two species of Thlaspi, one a Zn/Cd hyperaccumulator and the other a related nonaccumulator. In simple Cd(NO3)2 solutions, the electrode exhibited a Nernstian response in solutions with Cd2+ activities as low as 50 nm. Addition of Ca2+ to the calibration solutions did not influence the slope of the calibration curve but reduced the detection limit to a solution activity of 1 µm Cd2+. Addition of high concentrations of K+ and Mg2+ to the calibration solution to mimic the ionic composition of the cytoplasm affected neither the slope nor the sensitivity of the electrode, demonstrating the pH-insensitive electrode's potential for intracellular investigations. The electrode was assayed for selectivity and was shown to be at least 1000 times more selective for Cd2+ than for any of those potentially interfering ions tested. Flux measurements along the roots of the two Thlaspi species showed no differences in the pattern or the magnitude of Cd2+ uptake within the time frame considered. The Cd2+-selective microelectrode will permit detailed investigations of heavy-metal ion transport in plant roots, especially in the area of phytoremediation.

Journal Article↗