Current Response (current + response)

Distribution by Scientific Domains


Selected Abstracts


Regular Arrays of Microdisk Electrodes: Numerical Simulation as an Optimizing Tool to Maximize the Current Response and Minimize the Electrode Area Used

ELECTROANALYSIS, Issue 23 2006
Francois
Abstract Microdisk electrode arrays constitute an interesting tool for electroanalysis and electrocatalysis due to their increased sensitivity and excellent limits of detection. We first demonstrate that a 2-dimensional simulation based on the diffusion domain approximation can be used to simulate the response of such electrochemical systems and therefore improve their design and fabrication process. Second, we report data showing the peak current response for arrays at three typically employed voltage scan rate as a function of the number of disks per unit area and their radii. [source]


Saturation and self-inhibition of rat hippocampal GABAA receptors at high GABA concentrations

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2002
Katarzyna Mercik
Abstract Current responses to ultrafast ,-aminobutyric acid (GABA) applications were recorded from excised patches in rat hippocampal neurons to study the gating properties of GABAA receptors at GABA concentrations close to saturating ones and higher. The amplitude of currents saturated at approximately 1 mm, while the onset rate of responses reached saturation at 4,6 mm GABA. At high GABA concentrations (> 10 mm), the amplitude of current responses was reduced in a dose-dependent manner with a half-blocking GABA concentration of approximately 50 mm. The peak reduction at high GABA doses was accompanied by a tendency to increase the steady-state to peak ratio. At concentrations higher than 30 mm, this effect took the form of a rebound current, i.e. during the prolonged GABA applications, the current firstly declined due to desensitization onset and then, instead of decreasing towards a steady-state value, clearly increased. Both the self-inhibition of GABAA receptors by high GABA doses and rebound were clearly voltage dependent, being larger at positive holding potentials. The fast desensitization component accelerated with depolarization at all saturating [GABA] tested. The rebound phenomenon indicates that the self-block of GABAA receptors is state dependent, and suggests that the sojourn in the desensitized conformation provides a ,rescue' from the block. We propose that high GABA concentrations inhibit the receptors by direct occlusion of the channel pore having no effect on the receptor gating. [source]


Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S-Functionalized Self-Assembled Layers in Aqueous Solution

ELECTROANALYSIS, Issue 13 2009
Teresa, uczak
Abstract Gold nanoparticles (Au-NPs), cystamine (CA) and 3,3,-dithiodipropionic acid (DTDPA) modified gold bare electrodes were applied in voltammetric sensors for simultaneous detection of norepinephrine (NEP), ascorbic (AA) and uric (UA) acids. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1,,M to 600,,M M with the detection limit ,0.091,,M for the electrodes modified at 2D template and in the range of 0.1,,M to 700,,M M with the detection limit ,0.087,,M for the electrodes modified at 3D template The results have shown that using modified electrodes it is possible to perform electrochemical analysis of norepinephrine without interference of ascorbic and uric acids, whose presence is the major limitation in norepinephrine determination at a bare gold electrode. The modified SAMs electrodes show good selectivity, sensitivity, reproducibility and high stability. [source]


Voltammetric Antioxidant Analysis in Mineral Oil Samples Immobilized into Boron-Doped Diamond Micropore Array Electrodes

ELECTROANALYSIS, Issue 12 2009
Xiaohang Zhang
Abstract Mineral oil microdroplets containing the model antioxidant N,N -didodecyl- N,,N, -diethyl-phenylene-diamine (DDPD) are immobilized into a 100100 pore-array (ca. 10,,m individual pore diameter, 100,,m pitch) in a boron-doped diamond electrode surface. The robust diamond surface allows pore filling, cleaning, and reuse without damage to the electrode surface. The electrode is immersed into aqueous electrolyte media, and voltammetric responses for the oxidation of DDPD are obtained. In order to further improve the current responses, 20,wt% of carbon nanofibers are co-deposited with the oil into the pore array. Voltammetric signals are consistent with the oxidation of DDPD and the associated transfer of perchlorate anions (in aqueous 0.1,M NaClO4) or the transfer of protons (in aqueous 0.1,M HClO4). From the magnitude of the current response, the DDPD content in the mineral oil can be determined down to less than 1,wt% levels. Perhaps surprisingly, the reversible (or midpoint) potential for the DDPD oxidation in mineral oil (when immersed in 0.1 NaClO4) is shown to be concentration-dependent and to shift to more positive potential values for more dilute DDPD in mineral oil solutions. An extraction mechanism and the formation of a separate organic product phase are proposed to explain this behavior. [source]


Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self-Assembled Alkanethiol Monolayer on Gold Electrode

ELECTROANALYSIS, Issue 2 2009
Dan Zheng
Abstract A stable ordered mesoporous carbon (OMC) film electrode was successfully constructed by adsorbing OMC onto a self-assembled monolayer (SAM) of C18H37SH chemisorbed on the Au electrode. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrochemical methods were used to characterize the properties of the OMC film electrode. The adsorbed OMC can restore the heterogeneous electron transfer almost totally blocked by the alkanethiol monolayer. Nyquist plots show a sharply decrease of the charge transfer resistance (Rct) of the Fe(CN) couple at the OMC film electrode. Furthermore, the OMC film electrode is found to possess a significantly reduced interfacial capacitance and largely enhanced current response of hydrogen peroxide. This novel approach to the fabrication of stable OMC film electrode with excellent electrochemical properties is believed to be very attractive for electrochemical studies and electroanalytical applications. [source]


Construction of L -Lysine Sensor by Layer-by-Layer Adsorption of L -Lysine 6-Dehydrogenase and Ferrocene-Labeled High Molecular Weight Coenzyme Derivative on Gold Electrode

ELECTROANALYSIS, Issue 24 2008
Haitao Zheng
Abstract A ferrocene-labeled high molecular weight coenzyme derivative (PEI-Fc-NAD) and a thermostable NAD-dependent L -lysine 6-dehydrogenase (LysDH) from thermophile Geobacillus stearothermophilus were used to fabricate a reagentless L -lysine sensor. Both LysDH and PEI-Fc-NAD were immobilized on the surface of a gold electrode by consecutive layer-by-layer adsorption (LBL) technique. By the simple LBL method, the reagentless L -lysine sensor, with co-immobilization of the mediator, coenzyme, and enzyme was obtained, which exhibited current response to L -lysine without the addition of native coenzyme to the analysis system. The amperometric response of the sensor was dependent on the applied potential, bilayer number of PEI-Fc-NAD/LysDH, and substrate concentration. A linear current response, proportional to L -lysine concentration in the range of 1,120,mM was observed. The response of the sensor to L -lysine was decreased by 30% from the original activity after one month storage. [source]


Paste Electrode Based on Short Single-Walled Carbon Nanotubes and Room Temperature Ionic Liquid: Preparation, Characterization and Application in DNA Detection

ELECTROANALYSIS, Issue 12 2008
Xuzhi Zhang
Abstract A paste electrode (SWNT&RTIL PE) has been prepared using carboxylic group-functionalized short single-walled carbon nanotubes (SWNTs) mixed with 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6, one kind of room temperature ionic liquid, RTIL). Its electrochemical behavior was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in comparison with the paste electrode using mineral oil as a binder. Results highlighted the advantages of the paste electrode: not only higher conductivity, but also lower potential separation (,Ep), higher peak current (ip) and better reversibility towards dopamine (DA), methylene blue (MB) and K3[Fe(CN)6]. The SWNT&RTIL PE could be used to detect the number of guanine bases and adenine bases contents in per mol oligonucleotides according to the current response in the range of 0.05,2.0,nM. Based on the current response of guanine bases, oligonucleotides could be detected sensitively in the B,R buffer solution with a detection limit of 9.9,pM. The heterogeneous electron transfer rate constant (ks) of guanine bases contents in the oligonucleotides was investigated and its value was 0.90,s,1. In essence the SWNT&RTIL PE showed high sensitivity, reliability, stability and reproducibility for the detection of DNA. [source]


Regular Arrays of Microdisk Electrodes: Numerical Simulation as an Optimizing Tool to Maximize the Current Response and Minimize the Electrode Area Used

ELECTROANALYSIS, Issue 23 2006
Francois
Abstract Microdisk electrode arrays constitute an interesting tool for electroanalysis and electrocatalysis due to their increased sensitivity and excellent limits of detection. We first demonstrate that a 2-dimensional simulation based on the diffusion domain approximation can be used to simulate the response of such electrochemical systems and therefore improve their design and fabrication process. Second, we report data showing the peak current response for arrays at three typically employed voltage scan rate as a function of the number of disks per unit area and their radii. [source]


Preparation, Characterization and Analytical Applications of a New and Novel Electrically Conducting Polymer

ELECTROANALYSIS, Issue 15 2006
F. D'Eramo
Abstract In this study, a glassy carbon electrode (GC) was modified with an electropolymerized film of 1-naphthylamine (1-NAP) with a subsequent overoxidation treatment in 0.2,M sodium hydroxide solution. This polymer p-1-NAPox film coated GC electrode was used for the selective determination of dopamine (DA) in the presence of a triple concentration of ascorbic acid (AA). These studies were performed using cyclic voltammetry and square-wave voltammetry at physiological pH. p-1-NAPox shows an attractive permselectivity, a marked enhancement of the current response and antifouling properties when compared to a bare GC electrode activated in basic media. With a preconcentration time of 3,minutes at open circuit, linear calibration plots were obtained for DA in buffer solution (pH,7.4) over the concentration range from 110,6,110,4 M with a detection limit of 1.5910,7 M. [source]


Scanning Electrochemical Microscopy as an In Vitro Technique for Measuring Convective Flow Rates Across Dentine and the Efficacy of Surface Blocking Treatments

ELECTROANALYSIS, Issue 3 2005
Julie
Abstract Scanning electrochemical microscopy (SECM) is shown to be a powerful technique for both the measurement of local solution velocities through human dentine slices, in vitro, and for assessing quantitatively the effect of surface treatments on the flow process. SECM employs a small ultramicroelectrode (micron dimensions) as an imaging probe to provide information on the topography and transport characteristics of dentine, with high spatial resolution. In these studies the dentine sample is a membrane in a two compartment cell, which contains solutions of identical composition, including a redox active mediator (Fe(CN). In the absence of an applied pressure, the transport-limited current response at the probe electrode is due to diffusion of Fe(CN) to the UME, which depends on the probe to sample separation. Under an applied hydrostatic pressure, hydrodynamic flow across the sample enhances mass transport to the UME. With this methodology it was possible to accurately measure effective fluid velocities, by recording tip currents with and without pressure, and assess the efficacy of potential flow retarding agents for the treatment of dentinal hypersensitivity. For native dentine, the solution velocity was found to vary dramatically with location on the sample. The application of a glycerol monooleate - base paste treatment to the surface of dentine was found to lower local flow velocities significantly. This electroanalytical methodology is simple to implement and is generally applicable to assessing the efficacy and mode of action of a wide variety of potential fluid flow retarding agents. [source]


Amperometric Detection of Catecholamine Neurotransmitters Using Electrocatalytic Substrate Recycling at a Laccase Electrode

ELECTROANALYSIS, Issue 2 2005
Yvonne Ferry
Abstract An enzyme electrode based on the coimmobilization of an osmium redox polymer and laccase on glassy carbon electrodes has been applied to ultra sensitive amperometric detection of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine, resulting in nanomolar detection limits, as low as 4,nM for dopamine. The sensitivity of the electrode is due to signal amplification via oxidation of the catecholamine by the immobilized laccase, which is regenerated by concomitant reduction of oxygen to water, coupled to the electrocatalytic re-reduction of the oxidized catecholamine by the osmium redox complex: electrocatalytic substrate recycling. In addition because the sensor can be operated in reductive mode at ,0.2,V (vs. Ag/AgCl), noise and interferences are diminished. Combined with its high sensitivity this enzyme electrode also exhibited excellent selectivity allowing the detection of catecholamines in the presence of ascorbic acid. However, differentiation between the current responses achieved for the three catecholamines is not possible. The effective mode of constant recycling, resulting in amplification of the current response, of the laccase enzyme electrode sensor combined with the inherent advantages of using electrochemical techniques holds great promise for the future of catecholamine detection and monitoring. [source]


A Tubulin-Based Quantitative Assay for Taxol (Paclitaxel) with Enzyme Channeling Sensing

ELECTROANALYSIS, Issue 8 2004
Shin-ichiro Suye
Abstract We report the development and characterization of a biosensor for sensitive and rapid determination of the anticancer agent Taxol (paclitaxel). The sensor is based on the interaction of Taxol with its receptor protein tubulin in conjunction with the separation-free immunosensor technique of enzyme channeling. The sensor system consisted of a three electrode electrochemical cell containing a graphite carbon electrode modified with glucose oxidase and tubulin as working electrode poised at +40,mV (vs. Ag/AgCl). Addition of Taxol, horseradish peroxidase labeled Taxol, glucose and potassium iodide to the cell generated a cathodic current response that was proportional to the concentration of Taxol in the range of 10 to 1,000,pM. [source]


Enzyme-catalyzed amperometric oxidation of neurotransmitters in chip-capillary electrophoresis

ELECTROPHORESIS, Issue 12 2004
Maria A. Schwarz
Abstract The determination of biogenic monoamines by enzyme-catalyzed oxidation after electrophoretical separation on a microfluidic chip decreases their detection limits significantly. An amperometric system with a chemically amplified response for neurotransmitters and their metabolites is presented. The principle is the rapid cyclic oxidation of the analyte on the amperometric detector in the presence of the redoxactive enzyme glucose oxidase in the capillary electrophoresis buffer. With this approach, detection limits in the range of 10,7,10,8M could be reached. Because of the good linearity between the current response and the concentration of catecholamines and their metabolites at concentrations up to 300 ,M, this method is attractive for the analytical detection at low concentration levels such as in biological fluids. [source]


Mixed p-z approach for analytical analysis of an induction motor fed from space-vector PWM voltage source inverter

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 6 2002
J. Klima
This paper proposes an analytical method for calculating both the steady-state and transient performance of an induction motor fed from the three-phase voltage source inverter. As a modulation technique of the inverter we consider space vector modulation. The proposed method makes use of the Laplace and modified Z-transformation of the space vectors (mixed p-z approach) to predict current response of induction motor. From the Laplace transform of the stator voltage vector we can also derive Fourier analysis to predict the voltage harmonic spectrum. Experimental tests have been carried out confirming the validity of the analytical results. [source]


Hard Macrocellular Silica Si(HIPE) Foams Templating Micro/Macroporous Carbonaceous Monoliths: Applications as Lithium Ion Battery Negative Electrodes and Electrochemical Capacitors

ADVANCED FUNCTIONAL MATERIALS, Issue 19 2009
Nicolas Brun
Abstract By using Si(HIPEs) as hard, exotemplating matrices, interconnected macro-/microporous carbon monolith-type materials with a surface area of around 600,m2 g,1 are synthesized and shaped. The carbonaceous foams exhibit a conductivity of 20,S cm,1, addressed with excellent mechanical properties (Young's modulus of 0.2,GPa and toughness of 13,J g,1, when the carbon core is optimized). The above-mentioned specificities, combined with the fact that the external shape and size can be easily designed on demand, are of primary importance for applications. The functionality of these carbonaceous monoliths is tested as both an electrochemical capacitor and a lithium ion negative electrode. The electrochemical capacitors' voltage,current profiles exhibit a non-ideal rectangular response, confirming the double-layer behavior of the carbon studied, while the charge-discharge current profile of the electric double-layer capacitor is directly proportional to the scan where the current response during charge and discharge exhibits high reversibility. When acting as a lithium ion negative electrode, after initial irreversibility, a good cyclability is obtained, associated with a stable capacity of 200,mA h g,1 during the first 50 cycles at a reasonable current density (C/10). [source]


Electrophysiological characterization of electrolyte and nutrient transport across the small intestine in horses

JOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 3 2009
A. Cehak
Summary The aim of this study was to characterize the transport mechanisms of electrolytes and nutrients across the jejunum of nine healthy horses electrophysiologically. The stripped mucosa was mounted in Ussing chambers and tissue conductances (Gt) and short circuit currents (Isc) were continuously monitored. After blocking the sodium and potassium channels with amiloride, tetraethylammonium chloride (TEA) and barium, chloride secretion was stimulated by carbachol and forskolin. Subsequently, chloride channels were inhibited by 4,4,-diisothiocyanato-stilbene-2,2,-disulfonic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, CFTRinh -172, N -(2-naphtalenyl)-(3.5-dibromo-2.4-dihydroxyphenyl)methylene glycine hydrazide (GlyH-101) and glibenclamide and their dose,response effect was investigated. The response to glucose, l -alanine and glycyl- l -glutamine was determined at two different mucosal pH values (pH 7.4 and 5.4 respectively). Mean basal Isc was ,0.47 0.31 ,Eq/cm2h and mean Gt was 22.17 1.78 mS/cm2. Amiloride and TEA did not alter the baseline Isc. Barium, carbachol and forskolin significantly increased Isc. Irrespective of the dose, none of the chloride inhibitors changed Isc. All nutrients induced a significant increase in Isc with the increase being significantly higher at pH 7.4 than at pH 5.4. In conclusion, there is evidence that chloride secretion in horses may be different from respective transport mechanisms in other species. The glucose absorption is suggestive of a sodium-dependent glucose cotransporter 1. However, a decrease in luminal pH did not stimulate current response to peptides as shown for other mammals. [source]


Molecular rectification in metal,bridge molecule,metal junctions

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2010
Yaqing Liu
Abstract Molecular bridged nanocontacts allow direct electrical addressing of electroactive molecules, which is of interest for the development of molecular based electronic devices. In the present paper, the electroactive molecule 6-ferrocenyl-1-hexanethiol (Fc-HT) was integrated into metal,bridge,metal (MBM) junctions assembled in a scanning tunneling microscope (STM) setup. A diode-like behavior was observed from the current/bias (It/Vb) signal through Au (substrate)/Fc-HT/Au (tip) junction, which presented an asymmetric current response due to the resonant tunneling between metal electrode and ferrocenylthiol molecules. With gate electrode modulation, the enhancement of the tunneling current can be controlled, which allows to tune the direction of the current rectification. Our investigations demonstrated that ferrocenylthiol bridged MBM nanostructure has potential applications in the future design of higher-order heterojunctions components in combination with electrochemical logic gates. [source]


Nanofibrous polyaniline thin film prepared by plasma-induced polymerization technique for detection of NO2 gas

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 9 2010
Ashutosh Tiwari
Abstract A nanofibrous polyaniline (PANI) thin film was fabricated using plasma-induced polymerization method and explored its application in the fabrication of NO2 gas sensor. The effects of substrate position, pressure, and the number of plasma pulses on the PANI film growth rate were monitored and an optimum condition for the PANI thin film preparation was established. The resulting PANI film was characterized with UV,visible spectrophotometer, FTIR, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The PANI thin film possessed nanofibers with a diameter ranging from 15 to 20 nm. The NO2 gas sensing behavior was studied by measuring the change in electrical conductivity of PANI film with respect to NO2 gas concentration and exposure time. The optimized sensor exhibited a sensitivity factor of 206 with a response time of 23 sec. The NO2 gas sensor using nanofibrous PANI thin film as sensing probe showed a linear current response to the NO2 gas concentration in the range of 10,100 ppm. Copyright 2009 John Wiley & Sons, Ltd. [source]


Response properties of isolated mouse olfactory receptor cells

THE JOURNAL OF PHYSIOLOGY, Issue 1 2001
Johannes Reisert
1Response properties of isolated mouse olfactory receptor cells were investigated using the suction pipette technique. Cells were exposed to the odour cineole or to solutions of modified ionic content by rapidly changing the solution superfusing the cilia. All experiments were performed at 37C. 2Mouse olfactory receptor cells displayed a steep dependence of action potential frequency on stimulus concentration, a 3-fold increase in stimulus concentration often saturating the firing frequency at 200-300 Hz. The receptor current increased more gradually with increasing cineole concentration and did not saturate within the 100-fold range of cineole concentrations applied. 3When stimulated for 30 s with a low odour concentration, cells responded with sporadic spike firing. Higher concentrations led to the generation of a large receptor current at the onset of stimulation which returned to baseline levels within a few seconds, accompanied during its rising phase by a short burst of action potentials. Thereafter an oscillating response pattern was observed during the remainder of the stimulus, consisting of repetitive increases in receptor current of around 1 s duration accompanied by short bursts of action potentials. 4Olfactory adaptation was studied by comparing the responses to two closely spaced odour stimuli. The response to the second odour stimulus recovered to 80% of its original magnitude when the cell was superfused with Ringer solution during the 5 s interval between odour exposures. In contrast, exposure to a choline-substituted low Na+ solution between odour stimuli had two effects. First, the receptor current response to the first odour stimulus did not terminate as quickly as in the presence of Na+, suggesting the presence of a Na+ -Ca2+ exchanger. Second, the response to the second stimulus only recovered to 55% of its original magnitude, demonstrating the involvement of Na+ -Ca2+ exchange in the recovery of sensitivity in mouse olfactory receptor cells following stimulation. [source]


Simultaneous analysis of physiological and electrical output changes in an operating microbial fuel cell with Shewanella oneidensis,

BIOTECHNOLOGY & BIOENGINEERING, Issue 3 2009
Justin C. Biffinger
Abstract Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high-throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR-1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR-1, with both air-exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR-1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR-1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points. Biotechnol. Bioeng. 2009;103: 524,531. Published 2009 Wiley Periodicals, Inc. [source]


Positive allosteric modulation of ,7 neuronal nicotinic acetylcholine receptors: lack of cytotoxicity in PC12 cells and rat primary cortical neurons

BRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2009
Min Hu
Background and purpose:, ,7-Nicotinic acetylcholine receptors (,7 nAChRs) play an important role in cognitive function. Positive allosteric modulators (PAMs) amplify effects of ,7 nAChR agonist and could provide an approach for treatment of cognitive deficits in neuropsychiatric diseases. PAMs can either predominantly affect the apparent peak current response (type I) or increase both the apparent peak current response and duration of channel opening, due to prolonged desensitization (type II). The delay of receptor desensitization by type II PAMs raises the possibility of Ca2+ -induced toxicity through prolonged activation of ,7 nAChRs. The present study addresses whether type I and II PAMs exhibit different cytotoxicity profiles. Experimental approach:, The present studies evaluated cytotoxic effects of type I PAM [N-(4-chlorophenyl)]-,-[(4-chloro-phenyl)-aminomethylene]-3-methyl-5-isoxazoleacet-amide (CCMI) and type II PAM 1-[5-chloro-2,4-dimethoxy-phenyl]-3-[5-methyl-isoxazol-3-yl]-urea (PNU-120596), or 4-[5-(4chloro-phenyl)-2-methyl-3-propionyl-pyrrol-1-yl]-benzenesulphonamide (A-867744). The studies used cultures of PC12 cells and primary cultures of rat cortical neuronal cells. Key results:, Our results showed that neither type I nor type II PAMs had any detrimental effect on cell integrity or cell viability. In particular, type II PAMs did not affect neuron number and neurite outgrowth under conditions when ,7 nAChR activity was measured by Ca2+ influx and extracellular signal-regulated kinases 1 and 2 phosphorylation, following exposure to ,7 nAChR agonists. Conclusions and implications:, This study demonstrated that both type I and type II ,7 nAChR selective PAMs, although exhibiting differential electrophysiological profiles, did not exert cytotoxic effects in cells endogenously expressing ,7 nAChRs. [source]


Heterogeneous Electron Transfer and Oxygen Reduction Reaction at Nanostructured Iron(II) Phthalocyanine and Its MWCNTs Nanocomposites

ELECTROANALYSIS, Issue 9 2010
Solomon
Abstract Electron transfer and oxygen reduction dynamics at nanostructured iron(II) phthalocyanine/multi-walled carbon nanotubes composite supported on an edge plane pyrolytic graphite electrode (EPPGE-MWCNT-nanoFePc) platform have been reported. All the electrodes showed the category 3 diffusional behaviour according to the Davies,Compton theoretical framework. Both MWCNTs and MWCNT-nanoFePc showed huge current responses compared to the other electrodes, suggesting the redox processes of trapped redox species within the porous layers of MWCNTs. Electron transfer process is much easier at the EPPGE-MWCNT and EPPGE-MWCNT-nanoFePc compared to the other electrodes. The best response for oxygen reduction reaction was at the EPPGE-MWCNT-nanoFePc, yielding a 4-electron process. [source]


Voltammetric Antioxidant Analysis in Mineral Oil Samples Immobilized into Boron-Doped Diamond Micropore Array Electrodes

ELECTROANALYSIS, Issue 12 2009
Xiaohang Zhang
Abstract Mineral oil microdroplets containing the model antioxidant N,N -didodecyl- N,,N, -diethyl-phenylene-diamine (DDPD) are immobilized into a 100100 pore-array (ca. 10,,m individual pore diameter, 100,,m pitch) in a boron-doped diamond electrode surface. The robust diamond surface allows pore filling, cleaning, and reuse without damage to the electrode surface. The electrode is immersed into aqueous electrolyte media, and voltammetric responses for the oxidation of DDPD are obtained. In order to further improve the current responses, 20,wt% of carbon nanofibers are co-deposited with the oil into the pore array. Voltammetric signals are consistent with the oxidation of DDPD and the associated transfer of perchlorate anions (in aqueous 0.1,M NaClO4) or the transfer of protons (in aqueous 0.1,M HClO4). From the magnitude of the current response, the DDPD content in the mineral oil can be determined down to less than 1,wt% levels. Perhaps surprisingly, the reversible (or midpoint) potential for the DDPD oxidation in mineral oil (when immersed in 0.1 NaClO4) is shown to be concentration-dependent and to shift to more positive potential values for more dilute DDPD in mineral oil solutions. An extraction mechanism and the formation of a separate organic product phase are proposed to explain this behavior. [source]


Microwave-Assisted Electroanalysis: A Review

ELECTROANALYSIS, Issue 2 2009

Abstract Microwave-assisted electrochemistry is critically discussed with a focus on the fundamental aspects of the processes involved and its applications in electroanalysis. The concept of direct and nondirect heated electrodes is discussed, and simulation work is evaluated. Microwave-assisted electrochemistry predominantly results in higher current responses (up to 2 magnitudes higher) due to increased temperature and mass transport to the active electrodes. Temperature gradients at microwave-affected electrodes may exceed 105 K/cm, with temperature hotspots found in the thin diffusion layers set up at ultramicroelectrodes. Research into microwave-assisted electroanalysis can lead to enhanced capillary electrophoresis detection, improved stripping voltammetry and development of new high temperature methods. [source]


FIA Determination of Paracetamol in Pharmaceutical Drugs by Using Gold Electrodes Modified with a 3-Mercaptopropionic Acid Monolayer

ELECTROANALYSIS, Issue 9 2006
Valber
Abstract A flow injection analysis (FIA) method for the determination of paracetamol in pharmaceutical drugs using a gold electrode modified with a self-assembled monolayer (SAM) of 3-mercaptopropionic acid is described. At optimized experimental conditions the dynamic concentration range was 0.15 to 15.0,mg L,1 with a detection limit of 0.2,,g mL,1 (S/N=3). The repeatability of current responses for injections of 10,,mol L,1 paracetamol was evaluated to be 3.2% (n=30) and the analytical frequency was 180,h,1. The lifetime of the modified electrode was found to be 15 days. The results obtained by using the proposed amperometric method for paracetamol determination in four different drug samples compared well with those found by spectrophotometry. [source]


Voltammetric Monitoring and Speciation of Copper Ions in Italian "Grappa" with Platinum Microelectrodes

ELECTROANALYSIS, Issue 7 2006
Antonietta Baldo
Abstract A linear sweep voltammetric (LSV) investigation and the anodic stripping voltammetric (ASV) detection of copper ions in ethanol-water mixtures and grappa samples are reported. The measurements are carried out by using platinum microdisk electrodes. Ethanol-water mixtures with ethanol content in the range 40,100,vol%, commercially available and raw grappa samples having ethanol content in the above range are examined. From LSV measurements of copper (II) ions added to the samples, the formation of intermediate copper (I) soluble species, which are stabilized mainly by the naturally occurring organic compounds present in the real samples, is observed. The analysis of LSV and ASV current responses against added Cu2+ ions provides linear trends over the concentration range 510,5,510,3,M and 510,7,510,5,M, respectively. The sensitivity depends on the ethanol content in the mixture and, as expected, it is the higher the lower the viscosity of the medium. In particular, it varies from 1.54 to 3.53,nA mM,1 and from 0.114 to 0.263,nA ,M,1 for LSV and ASV measurements, respectively, upon changing the ethanol content from 40 to 100,vol%. In the same range of ethanol content, detection limits obtained by ASV vary from 0.27 to 0.15,,M, respectively. Labile or total copper contents in the grappa samples are determined by ASV measurements performed in the untreated matrices or in the samples acidified with 0.1,M HClO4, respectively. Finally, acidification of the samples with different amounts of HClO4 allows also some speciation investigations to be performed. [source]


Amperometric Detection of Catecholamine Neurotransmitters Using Electrocatalytic Substrate Recycling at a Laccase Electrode

ELECTROANALYSIS, Issue 2 2005
Yvonne Ferry
Abstract An enzyme electrode based on the coimmobilization of an osmium redox polymer and laccase on glassy carbon electrodes has been applied to ultra sensitive amperometric detection of the catecholamine neurotransmitters dopamine, epinephrine and norepinephrine, resulting in nanomolar detection limits, as low as 4,nM for dopamine. The sensitivity of the electrode is due to signal amplification via oxidation of the catecholamine by the immobilized laccase, which is regenerated by concomitant reduction of oxygen to water, coupled to the electrocatalytic re-reduction of the oxidized catecholamine by the osmium redox complex: electrocatalytic substrate recycling. In addition because the sensor can be operated in reductive mode at ,0.2,V (vs. Ag/AgCl), noise and interferences are diminished. Combined with its high sensitivity this enzyme electrode also exhibited excellent selectivity allowing the detection of catecholamines in the presence of ascorbic acid. However, differentiation between the current responses achieved for the three catecholamines is not possible. The effective mode of constant recycling, resulting in amplification of the current response, of the laccase enzyme electrode sensor combined with the inherent advantages of using electrochemical techniques holds great promise for the future of catecholamine detection and monitoring. [source]


Electroanalysis at Diamond-Like and Doped-Diamond Electrodes

ELECTROANALYSIS, Issue 17 2003
Richard
Abstract Diamond as a high performance material occupies a special place due to its in many ways extreme properties, e.g., hardness, chemical inertness, thermal conductivity, optical properties, and electric characteristics. Work mainly over the last decade has shown that diamond also occupies a special place as an electrode material with interesting applications in electroanalysis. When made sufficiently electrically conducting for example by boron-doping, ,thin film' and ,free,standing' diamond electrodes exhibit remarkable chemical resistance to etching, a wide potential window, low background current responses, mechanical stability towards ultrasound induced interfacial cavitation, a low ,stickiness' in adsorption processes, and a high degree of ,tunability' of the surface properties. This review summarizes some of the recent work aimed at applying conductive (boron-doped) diamond electrodes to improve procedures in electroanalysis. [source]


Presynaptic muscarinic acetylcholine receptors suppress GABAergic synaptic transmission in the intermediate grey layer of mouse superior colliculus

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2004
Fengxia Li
Abstract The intermediate grey layer (the stratum griseum intermediale; SGI) of the superior colliculus (SC) receives cholinergic inputs from the parabrachial region of the brainstem. It has been shown that cholinergic inputs activate nicotinic acetylcholine (nACh) receptors on projection neurons in the SGI. Therefore, it has been suggested that they facilitate the initiation of orienting behaviours. In this study, we investigated the effect of muscarinic acetylcholine (mACh) receptor activation on GABAergic synaptic transmission to SGI neurons using the whole-cell patch-clamp recording technique in slice preparations from mice. The GABAA receptor-mediated inhibitory postsynaptic currents (IPSCs) evoked in SGI neurons by focal electrical stimulation were suppressed by bath application of 10 m muscarine chloride. During muscarine application, both the paired-pulse facilitation index and the coefficient of variation of IPSCs increased; however, the current responses induced by a transient pressure application of 1 mm GABA were not affected by muscarine. Muscarine reduced frequencies of miniature IPSCs (mIPSCs) while the amplitudes of mIPSCs remained unchanged. These results suggestd that mAChR-mediated inhibition of IPSCs was of presynaptic origin. The suppressant effect of muscarine was antagonized by an M1 receptor antagonist, pirenzepine dihydrochloride (1 m), and a relatively specific M3 receptor antagonist, 4-DAMP methiodide (50 nm). By contrast, an M2 receptor antagonist, methoctramine tetrahydrochloride (10 m), was ineffective. These results suggest that the cholinergic inputs suppress GABAergic synaptic transmission to the SGI neurons at the presynaptic site via activation of M1 and, possibly, M3 receptors. This may be an additional mechanism by which cholinergic inputs can facilitate tectofugal command generation. [source]


Bidirectional modulation of visual plasticity by cholinergic receptor subtypes in the frog optic tectum

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2003
Chuan-Jiang Yu
Abstract Cholinergic input to the optic tectum is necessary for visual map maintenance. To understand why, we examined the effects of activation of the different cholinergic receptor subtypes in tectal brain slices and determined whether the retinotectal map was affected by manipulations of their activity in vivo. Both ,-bungarotoxin sensitive and insensitive nicotinic receptor agonists increased spontaneous postsynaptic currents (sPSCs) in a subpopulation of patch-clamped tectal cells; application of subtype selective receptor antagonists reduced nicotine-induced increases in sPSCs. Activation of ,-bungarotoxin insensitive nicotinic receptors also induced substantial inward current in some cells. Muscarinic receptor mediated outward current responses were blocked by the M2-like muscarinic receptor antagonists himbacine or AF-DX 384 and mimicked by application of the M2-like agonist oxotremorine. A less frequently observed muscarinic response involving a change in sPSC frequency appeared to be mediated by M1-like muscarinic receptors. In separate experiments, pharmacological manipulation of cholinergic receptor subtype activation led to changes in the activity-dependent visual map created in the tectum by retinal ganglion cell terminals. Chronic exposure of the tectum to either ,-bungarotoxin insensitive, ,-bungarotoxin sensitive or M1-like receptor antagonists resulted in map disruption. However, treatment with the M2-like receptor antagonist, AF-DX 384, compressed the map. We conclude that nicotinic or M1-like muscarinic receptors control input to tectal cells while ,-bungarotoxin insensitive nicotinic receptors and M2-like muscarinic receptors change tectal cell responses to that input. Blockade of the different cholinergic receptor subtypes can have opposing effects on map topography that are consistent with expected effects on tectal cell activity levels. [source]