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At least 1,135 records · Page 63Linked to original sources
PubMed2002

Response times of carbon fiber microelectrodes to dynamic changes in catecholamine concentration.

The electrode response time and the measured concentrations during dynamic catecholamine changes were compared using constant potential amperometry and fast-scan cyclic voltammetry. The amperometric response to a rectangular pulse of catecholamine is more rectangular than the cyclic voltammetric response; however, the response times are very similar when, during cyclic voltammetry, the temporal lag due to adsorption and desorption of catecholamine to the electrode is removed by deconvolution. Deconvolution of cyclic voltammetry data was applied to stimulated dopamine release in vivo, allowing for modeling of release and uptake kinetics and to measure catecholamine release from single cells, resulting in better resolution of peaks from single vesicles. In vitro postcalibrations were performed to calculate concentrations of catecholamine measured with cyclic voltammetry and amperometry. The addition of 600 microM ascorbic acid to the postcalibration buffer, allowing a catalytic reaction to regenerate dopamine, resulted in similar calculated concentrations for stimulated release of dopamine using amperometry and cyclic voltammetry. Using deconvoluted cyclic voltammetry to remove the response time lag and adding ascorbic acid to the calibration buffer, the shape and concentration of dynamic catecholamine changes are very similar when measured with constant potential amperometry and cyclic voltammetry.

Animals↗
PubMed2003

Detection of attomole quantities [correction of quantitites] of DNA targets on gold microelectrodes by electrocatalytic nucleobase oxidation.

The electrochemical detection of nucleic acid targets at low concentrations has a number of applications in diagnostics and pharmaceutical research. Self-assembled monolayers of alkanethiol-derivatized oligonucleotides on gold electrodes provide a useful platform for such detectors, and the electrocatalytic oxidation of nucleobases included in the DNA targets is a particularly sensitive method of electrochemical detection. A strategy has been developed for combining these two aspects by substituting either 7,8-dihydro-8-oxoguanine (8G) or 5-aminouridine (5U) into DNA targets. Upon hybridization of targets containing these modified nucleobases, electrocatalytic signals at probe-modified gold electrodes are observed in the presence of Os(bpy)(3)(2+), which oxidizes both 8G and 5U upon oxidation to the Os(III) state. Self-assembled monolayers were prepared on both macro (1.6 mm) and micro (25 microm) gold electrodes using published procedures involving C6-terminated alkanethiol oligonucleotides and mercaptohexanol as the diluent. The extent of electrode modification by the modified probe was assessed using radiolabeling and a standard chronocoulometry method; both approaches gave loading levels within expected ranges ((1-6) x 10(12) molecules/cm(2)). Hybridization of the modified targets where the non-native nucleobase was incorporated by solid-phase synthesis produced electrocatalytic signals from strands that were independently detected using radiolabeling and chronocoulometry. This result was used as a basis to develop an on-electrode amplification scheme where Taq polymerase was used to extend the immobilized DNA probes from solution-phase polymeric templates using modified nucleotriphosphates. This reaction produced an electrode that was modified with extended DNA containing the appropriate modified nucleotide. Radiolabeled nucleotide triphosphates were used to confirm the desired on-electrode DNA synthesis. When these electrodes were cycled in the presence of Os(bpy)(3)(2+), electrocatalytic signals were observed when as little as 40 amol (400 fM) of the desired target was present in the hybridization solution.

Catalysis↗
PubMed2006

Electropolymerization on microelectrodes: functionalization technique for selective protein and DNA conjugation.

A critical shortcoming of current surface functionalization schemes is their inability to selectively coat patterned substrates at micrometer and nanometer scales. This limitation prevents localized deposition of macromolecules at high densities, thereby restricting the versatility of the surface. A new approach for functionalizing lithographically patterned substrates that eliminates the need for alignment and, thus, is scalable to any dimension is reported. We show, for the first time, that electropolymerization of derivatized phenols can functionalize patterned surfaces with amine, aldehyde, and carboxylic acid groups and demonstrate that these derivatized groups can covalently bind molecular targets, including proteins and DNA. With this approach, electrically conducting and semiconducting materials in any lithographically realizable geometry can be selectively functionalized, allowing for the sequential deposition of a myriad of chemical or biochemical species of interest at high density to a surface with minimal cross-contamination.

Benzaldehydes↗
PubMed2006

Microwave induced jet boiling investigated via voltammetry at ring-disk microelectrodes.

High intensity microwave radiation is (self-)focused at metal electrodes immersed in aqueous electrolyte solutions to generate highly localized superheating and convection effects. It is shown that, for an electrode pointing downward, low intensity microwave radiation causes density driven convective flow (upward), which at the onset of boiling abruptly switches to a fast jet of liquid moving away from the electrode surface (downward). This "jet-boiling" phenomenon allows extremely high rates of mass transport and mixing to be realized at the electrode surface. Cyclic voltammograms obtained at electrodes placed into a microwave field show very strong mass transport enhancement effects. Cyclic voltammograms recorded at a Pt/Pt ring-disk electrode system (r(1) = 25 microm, r(2) = 32 microm, r(3) = 32.4 microm) in the presence of microwave radiation are employed to further explore mass transport effects under microwave conditions. Mass transport coefficients, collection efficiencies, and temperatures are determined as a function of microwave intensity.

Chemistry, Physical↗
PubMed2004

Giant lipid vesicles impaled with glass microelectrodes: GigaOhm seal by membrane spreading.

Giant unilamellar lipid vesicles could be perfect systems to study ion channels in the environment of lipid membranes with defined chemical and physical properties. Prerequisite for electrical measurements is an intravesicular electrical contact. We describe the impalement of giant lipid vesicles by glass micropipet electrodes with a tight seal. To avoid displacement or burst during impalement, the vesicles are immobilized in relaxed conditions by microscopic picket fences of polyimide. The outer surface of the pipets is selectively coated with silanes or polylysine. Structurally, the impalement is verified by ejecting a fluorescent solution out of the pipet. For electrical characterization, current pulses are applied to the pipet and voltage transients are recorded. The data are evaluated in terms of the capacitance and effective resistance of the membrane. Directly after impalement, we observe a seal resistance up to 1.2 GOmega that continuously decays within a period of up to 20 min until it suddenly disappears without burst of the vesicle. During impalement, a spreading of the vesicle membrane along the outer surface of the pipets is observed using a fluorescent membrane-bound dye. We assign the tight pipet-vesicle contact to spreading of the lipid bilayer by a rolling mechanism and the loss of resistance to micro- and macropores that are induced by the resulting membrane tension. Limitation of spreading is attempted with barriers on the pipet.

Electric Impedance↗