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At least 109 records · Page 6Linked to original sources
PubMed1997

Assembling and evaluation of new dehydrogenase enzyme electrode probes obtained by electropolymerization of aminobenzine isomers and PQQ on gold, platinum and carbon electrodes.

Pt, Au and graphite electrodes have been coated by electropolymerization of 1,2-, 1,3-, 1,4-diaminobenzene (DAB) and 4-aminobiphenyl in the presence of PQQ using cyclic voltammetry. The activity of the modified electrodes for the oxidation of paracetamol, ascorbic and uric acid was reduced by approximately 90% as compared to the bare electrodes. Polymerization in the presence 4,5-dihydro-4,5-dioxo-1H-pyrrolo(2,3-f)quinoline-2,7,9-tricarboxilic+ ++ acid, pyrroloquinolinequinone (PQQ) led, after optimization, to electrodes capable of catalysing the electrooxidation of beta-nicotinamide adenine dinucleotide, reduced form (NADH), in the range 10(-4)-10(-2) mol/l with a detection limit of 5 x 10(-5) mol/l. Amperometric measurements of NADH have been carried out at +0.2 V and the efficiency of different electrodes based on different materials has been studied. By co-entrapment of dehydrogenase highly selective enzymes, electrodes for glucose, L-lactate and L-glutamate were obtained. Dehydrogenase substrates such as glucose, lactate and glutamate were measured in the range 5 x 10(-5)-1 x 10(-2) mol/l, with detection limits of 10(-5) and 5 x 10(-6) mol/l, respectively. Probe stability under non-dynamic conditions was evaluated over 2 months. All the probes showed a decrease of 10% over 1 month and a residual activity of 50% over 2 months.

Aminobiphenyl Compounds↗
PubMed2002

The Sonogel-Carbon electrode as a sol-gel graphite-based electrode.

In this work, a novel sol-gel-based procedure to obtain solid carbon composite electrodes is proposed. The procedure is based on the use of sonocatalysis to apply high-energy ultrasound directly to the precursors; this way, ultrasonic cavitation is achieved so that hydrolysis with acidic water is promoted in the absence of any additional solvent and the time needed to get a unique phase is reduced drastically. The mix of sonogel with spectroscopic grade graphite leads to a new type of sol-gel electrode: the Sonogel-Carbon electrode. The amount of water, necessary for hydrolysis to occur, has been studied, as well as the sol pH value and the electrochemical behavior of the Sonogel-Carbon electrode in Britton-Robinson buffer. Mechanical renewal of the electrodes surfaces and background signal stability for at least 42 days have been also tested. We have carried out some tests to check the ability of the synthesized material to give electrochemical response when redox species are present in the background electrolyte. Mechanical and electrochemical studies indicate that the Sonogel-Carbon electrode shows good properties for use as an electrochemical sensor.

Journal Article↗
PubMed1983

Continuous registration of membrane input resistances of small plant cells using a double-pulse current clamp technique for single-electrode impalements : comparison with the conventional two-electrode method.

To measure the cell input resistance in Elodea leaf cells, a new single-microelectrode method was explored by comparing the results with conventional two-microelectrode experiments. The new method takes advantage of the difference in the frequency response curves between electrode and cell impedances. By application of electrical stimuli, which contain specific frequency bands, the different impedances can be analyzed separately. To get a distinct separation in the frequency response of cell and electrode, respectively, the electrode capacitance has to be compensated during the impalement. Different time constants of the cell membrane can be accounted for by adjustment of the stimulus length. It is shown that both the single- and the double-electrode method yield the same results, even if the cell input resistances change considerably during the course of the experiment. This demonstrates the usefulness of the new single-electrode method for continuous measurements of cell membrane resistances, especially in cells so small that the double-electrode method is no longer applicable.

Journal Article↗
PubMed1985

Urethral sphincter electromyography with vaginal surface electrodes: a comparison with sphincter electromyography recorded via periurethral coaxial, anal sphincter needle and perianal surface electrodes.

Urethral sphincter electromyography recording via vaginal surface electrodes was compared to simultaneous sphincter electromyographic registrations obtained with a periurethral coaxial needle electrode and perianal surface or needle electrodes in 10 neurologically intact women. Qualitative similarity of the vaginal surface and periurethral needle electrode recordings was found. Based on this and our previous studies, we conclude that electromyographic recording with vaginal surface electrodes offers a simple and reliable technique to evaluate the striated urethral sphincter during routine urodynamic studies in women.

Adult↗
PubMed1998

Effect of surface modifiers on the electrode reactions and conformation of cytochrome c3 adsorbed on a silver electrode.

Surface-enhanced resonance Raman scattering and electroreflectance voltammetry were used to investigate the effect of electrode surface modification on the structure and redox properties of cytochrome c3 immobilized on Ag surfaces. It is shown that the redox reactions of cytochrome c3 are more reversible at an 11-mercaptoundecanoic acid modified Ag electrode as compared to a bare metal surface. The heme of cytochrome c3 is in a mixed low and high spin state when adsorbed at the bare electrode, whereas only the low spin form is present on the 11-mercaptoundecanoic acid modified electrode, suggesting that the native conformation is maintained in the latter case. The reduction potential is close to that of the most positive macroscopic potential as determined by electroreflectance spectroscopy. In contrast, the reduction potential as determined by SERRS undergoes a large positive shift in the presence of 4,4'-bipyridine, the magnitude of which is dependent upon the concentration of 4,4'-bipyridine. These results indicate that the effect of the cytochrome c3 interaction with the 4,4'-bipyridine-modified surface is significantly different as compared to its interaction with the 11-mercaptoundecaodoic acid modified surface. Moreover, the results emphasize that electrode modifiers can have dramatically different effects on the redox properties of different proteins. It is well known that 4,4'-bipyridine acts as a redox promoter in the case of cytochrome c, whereas no electrochemical or electroreflectance response was observed in the case of cytochrome c3.

Adsorption↗
PubMed1992

Detection of motor unit action potentials with surface electrodes: influence of electrode size and spacing.

A model of the motor unit action potential was developed to investigate the amplitude and frequency spectrum contributions of motor units, located at various depths within muscle, to the surface detected electromyographic (EMG) signal. A dipole representation of the transmembrane current in a three-dimensional muscle volume was used to estimate detected individual muscle fiber action potentials. The effects of anisotropic muscle conductance, innervation zone location, propagation velocity, fiber length, electrode area, and electrode configuration were included in the fiber action potential model. A motor unit action potential was assumed to be the sum of the individual muscle fiber action potentials. A computational procedure, based on the notion of isopotential layers, was developed which substantially reduced the calculation time required to estimate motor unit action potentials. The simulations indicated that: 1) only those motor units with muscle fibers located within 10-12 mm of the electrodes would contribute significant signal energy to the surface EMG, 2) variation in surface area of electrodes has little effect on the detection depth of motor unit action potentials, 3) increased interelectrode spacing moderately increases detection depth, and 4) the frequency content of action potentials decreases steeply with increased electrode-motor unit territory distance.

Action Potentials↗
PubMed2004

Thick-film electrodes for measurement of superoxide and hydrogen peroxide based on direct protein-electrode contacts.

Cytochrome c was immobilized on screen-printed thick-film gold electrodes by a self-assembly approach using mixed monolayers of mercaptoundecanoic acid and mercaptoundecanol. Cyclic voltammetry revealed quasi-reversible electrochemical behavior of the covalently fixed protein with a formal potential of +10 mV vs. Ag/AgCl. Polarized at +150 mV vs. Ag/AgCl the electrode was found to be sensitive to superoxide radicals in the range 300-1200 nmol L(-1). Compared with metal needle electrodes sensitivity and reproducibility could be improved and combined with the easiness of preparation. This allows the fabrication of disposable sensors for nanomolar superoxide concentrations. By changing the electrode potential the sensor can be switched from response to superoxide radicals to hydrogen peroxide-another reactive oxygen species. H(2)O(2) sensitivity can be provided in the range 10-1000 micromol L(-1) which makes the electrode suitable for oxidative stress studies.

Animals↗
PubMed2006

Experimental hepatic radiofrequency ablation using wet electrodes: electrode-to-vessel distance is a significant predictor for delayed portal vein thrombosis.

The aim of this study was to examine possible explanatory variables associated with acute and delayed portal vein thrombosis after hepatic radiofrequency (RF) ablation using wet electrodes. Coagulations were created within 1.5 cm of the right portal vein (RPV) branch in 12 pigs with (n = 6) or without (n = 6) Pringle manoeuvre. Sham operations with Pringle manoeuvre were performed in four animals. Rotational portal venography was performed prior to ablation, 10 min after ablation and 4 days after ablation. Vessel diameters and vessel patency was determined from the portal venograms. Distance between the ablation electrode and RPV was measured from 3-dimensional reconstructions of the portal venograms. The portal veins were examined by microscopy. Delayed portal vein thrombosis was found in two of six animals in the Pringle group and three of six animals in the control group 4 days after ablation (P = 1.0, Fisher's exact test). All five occurrences of delayed portal vein thrombosis were found in the six animals with a distance between the ablation electrode and RPV of 5 mm or less (P = 0.030), indicating that the electrode-to-vessel distance may be an independent explanatory factor for delayed portal vein thrombosis after RF ablation with wet electrodes.

Animals↗
PubMed1994

Pacing thresholds of temporary epicardial electrodes: variation with electrode type, time, and epicardial position.

We compared the variation in pacing thresholds of two widely used temporary pacing electrodes at different epicardial sites in 67 patients after coronary artery operations performed with either cardioplegia or ventricular fibrillation. In 33 patients, a bare, braided pacing wire (DW) was placed on the right ventricle and a Medtronic localized epicardial electrode (MED), on each ventricle. In the other 34 patients, the DW wire was placed on the right atrium and a MED electrode, on each atrium. Pacing thresholds were measured at the time of placement; at 1 hour, 6 hours, and 12 hours postoperatively; and daily for 4 days. The pacing thresholds (mean +/- standard error of the mean) at implantation were as follows: DW wire = 0.93 +/- 0.08 V and MED electrode = 0.63 +/- 0.1 V in the ventricles and DW = 1.28 +/- 0.18 V and MED = 0.65 +/- 0.09 V in the atria. On the fourth postoperative day, the pacing thresholds were DW = 2.08 +/- 0.21 V and MED = 1.19 +/- 0.22 V in the ventricles and DW = 2.33 +/- 0.29 V and MED = 1.04 +/- 0.09 V in the atria. The pacing thresholds of both types of wire increased significantly over time, but this deterioration was more pronounced with the braided wire both on the ventricle and on the atrium. The pacing threshold patterns were not affected by chamber side or mode of myocardial preservation. The braided ventricular wire failed to capture after 24 hours in 9 of 30 patients, whereas the localized epicardial electrode captured in all instances (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗
PubMed1982

A new type of enzyme electrode: the ascorbic acid eliminator electrode.

A new type of enzyme electrode has been developed for in vivo electrochemical measurements which allows discrimination between ascorbic acid and catecholamines and their metabolites. The electrode employs the enzyme ascorbic acid oxidase held between the voltammetric electrode and solution by a dialysis membrane or immobilized on the outer surface of serous membrane from rat small intestine. The electrode gives linear calibration curves for all catecholamines and metabolites independent of any ascorbic acid concentrations significant in physiological measurements. The electrode has been tested in brain slice measurements and shown to respond to releases of catecholamines initiated by potassium ion stimulation.

Animals↗
PubMed1992

Mesial temporal subdural electrode as a substitute for depth electrode.

As a substitute for depth electrodes, mesial temporal subdural electrodes were devised. This electrode has a slender trapezoid shape and is easily introduced to the inner uppermost portion of the parahippocampal gyrus. Our results have shown that mesial temporal electrodes can detect not only interictal spikes but also subclinical and clinical seizure discharges from the mesiolimbic structures, and they have excellent capability for lateralization of the mesial temporal epileptic focus. If mesial temporal subdural strips are used in combination with lateral temporal subdural grids, comprehensive understanding of the focus distribution throughout the temporal lobes will be possible without using depth electrodes.

Adolescent↗
PubMed2006

The physiologically modulated electrode potentials at the depth electrode-brain interface in humans.

To study the modulated electrical potential specifically related to the electrode-brain interface (EBI) in deep brain stimulation (DBS) under physiological condition, we quantitatively identified the physiologically modulated electrode potentials by decomposing the local field potentials (LFPs) recorded from 11 patients (18 electrodes in four different brain regions) who underwent DBS, and correlated them with simultaneously recorded physiological signals of blood pressure (BP) and respiration. Results showed that electrode potentials were modulated by BP and respiration and could be detected as a specific component of the compound LFP signals with a mean (+/-S.D.) amplitude of 6.9+/-1.7 microV. The detection rate and amplitude of the modulated electrode potentials were independent from brain regions and neurological disorders. The current approach can be used to study the changes in properties of the EBI under physiological condition and to investigate the effects of the EBI on the 'crossing' current of either the neural signals to be recorded or the electrical pulses for neurostimulation.

Blood Pressure↗
PubMed1976

A simple procedure for positioning precordial ECG and VCG electrodes using an electrode locator.

Methodological differences in the placement of precordial ECG electrodes are a major problem in multicenter clinical trials and epidemiological studies. Trend analysis and realization of the full potential of computer programs for serial comparison demands reduction of technical sources of variation in the electrocardiogram (ECG) and vectorcardiogram (VCG) and particularly errors in locating ECG electrodes. The ECG electrodes locator described here reduces a major precordial uncertainty in the identification of the midclavicular and the anterior axillary lines. It simplifies positioning and provides a numeric record of the key precordial electrode positions, facilitating control of electrode placement errors in serial recordings.

Adult↗
PubMed1991

Peroxidase model electrodes: heme peptide modified electrodes as reagentless sensors for hydrogen peroxide.

A peroxidase model electrode was devised for reagentless sensing of hydrogen peroxide (H2O2). A small model molecule, which mimics the vicinity of the reaction center of a redox enzyme, can communicate electrochemically with an electrode. Heme nonapeptide (MW congruent to 1600) having peroxidase activity was adopted as a peroxidase model compound and was covalently immobilized on a tin oxide (SnO2) electrode as a roughly monomolecular layer. The modified electrode thus obtained responded to H2O2 at concentrations down to 10(-6) M without electron mediator or promoter, at a mild potential of +150 or +300 mV vs Ag/AgCl. In a batch system, the response reached a steady state in a few seconds. Measurements were possible also in a flow system with an assay time of 0.5-1.0 min/sample. The steady-state response of the electrode was kinetically analyzed.

Biosensing Techniques↗
PubMed2001

Measurement of the direct-current (Faradic) resistance of the electrode-electrolyte interface for commonly used electrode materials.

The direct-current (Faradic) resistance is important because it is the highest impedance that an electrode-electrolyte interface can attain. In this study, the Faradic resistance (Rf) of identical pairs of 0.5 cm2 electrodes of bare and chlorided silver, tin and chlorided tin, nickel-silver, copper, and carbon was measured in contact with 0.9% saline at room temperature. It was found that for positive and negative current flow, the data fit the expression Rf=Rf0 e(-alpha i) (with a high coefficient of determination), where Rf0 is the zero-current Faradic resistance and alpha is a constant that describes the manner in which Rf decreases with increasing current (i). It was found that chlorided silver exhibited the lowest Rf0; removing the chloride deposit increased Rf0 by more than sixfold. Likewise, chloriding tin reduced Rf0 by a factor of about 2. Electrolytically cleaning an electrode reduced Rf0. The highest value for Rf0 was for carbon. This paper concludes with a summary of the data for Rf0 scaled to 1 cm2 electrode area for the electrode materials measured in the present study and data from the published literature.

Biomedical Engineering↗
PubMed1993

[Comparison of the gold wire electrode with cotton wick electrode for electroretinography in small laboratory animals].

Using the gold wire and cotton wick electrodes, the electroretinograms of mice and rats were measured, and then they were compared. The results obtained were as follows: 1) There were no remarkable differences in the latencies and amplitudes of a- and b-waves, amplitudes and numbers of waves of oscillatories between two different electrodes. 2) It was easy to make and maintain the gold wire electrode as compared with the cotton wick electrode. From these results, it appears that the gold wire electrode is useful for measuring the electroretinogram of small laboratory animals.

Animals↗
PubMed1981

Chronic threshold of stimulating electrodes: comparison of activated vitreous carbon with conventional platinum-iridium electrodes in animal tests.

Electrodes made of vitreous carbon are inert, corrosion-resistant, inactive to electrocatalytic reactions and are especially biocompatible. Upon activation, they attain a capacitance of 20 to 40 mF and become "non-polarizable". Therefore, they should be particularly suitable as stimulating and sensing electrodes for cardiac pacemakers. The connective tissue layer that develops around the electrode because of the foreign-body reaction is less than 100 micron thick. The threshold rise, through lower than that of conventional Pt-Ir or ELGILOY electrodes, cannot be attributed exclusively to the connective tissue layer that is formed. Under favourable conditions, the threshold in animal experiments remains below 525 mV. Blood-spaces adjoining the electrodes are found at higher chronic threshold values.

Animals↗