Tubular Microring Electrode Sensor

A tubular ultra-microelectrode (UME) has two unique characteristics. First, the relatively small surface area of the gold ring at the tip of the electrode enables it to detect very low current. Secondly, the hollow interior of the electrode permits introduction of a very minute volume of analyte sample in the range of nano to pico-liters to the tip of the electrode for electrochemical analysis in an immiscible media. The high throughput capability of the tubular electrode is another attractive feature. The tubular microring gold electrode was used as a biosensor in conjunction with horse radish peroxidase to detect hydrogen peroxide in a 1-mL solution. Hydrogen peroxide was accurately detected from a range of 1-300 µM with a correlation coefficient of 0.9974. Electrochemical analysis was also carried out using the tubular microring electrode in a nano-liter aqueous droplet in nitrobenzene. Serving as a biosensor, in conjunction with horse radish peroxidase, hydrogen peroxide was accurately detected from a range of 3-300 µM with a correlation coefficient of 0.9987. Anodic stripping voltammetry (ASV) is a very sensitive method for the analysis of trace concentrations of electroactive species in solution. Traditionally mercury droplet electrodes are used to conduct the analysis; however due to the toxicity of mercury other material have, in the past, been investigated. Bismuth film electrodes have been found to offer high-quality stripping performance that compares favorably with that of mercury electrodes. A gold microring electrode plated with bismuth was used to reproducibly detect lead (Pb(II)) ions in solution at 30-300 ppb with a correlation coefficient of 0.9941. The gold microring electrode was also plated with bismuth-bromide, to increase the cathodic potential range, to reproducibly detect cadmium (Cd(II)) ions in solution from 100-500ppb with a correlation coefficient of 0.9924. Carbon is one of the preferred materials to use as support of many electrocatalysts for electrochemical studies. Carbon is a very inert material and has a desirable surface for electrical conductivity. Carbon films were formed on fused-silica capillary tubes by the carbonization of polyaniline polymer and also by the pyrolytic vapor deposition of benzene. The carbon film obtained by the pyrolytic vapor deposition of benzene was found to be electrically conductive. This carbon film on fused-silica capillary tubes was used to manufacture a tubular carbon microring electrode. Cyclic voltammograms of ferricyanide at the carbon microring electrode yielded sigmoidal (steady state) curves; as expected from a microelectrode.

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