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The flexibility of DNA is of central importance in biology, medicine, materials science, and mechanical engineering. In this study, we report an unprecedented electrochemical approach for investigating the flexibility of a short (typically 20-base), surface end-tethered single-stranded synthetic DNA oligonucleotide and of its postformed DNA duplex, taking as an example the homopolymer (dT)20 sequence in the regime of very high ionic strength ( approximately 1 M).

The electrochemical oxidation of dihydronicotinamide adenine dinucleotide (NADH) was studied in buffered aqueous media (pH 7.0) by single and multiple sweep voltammetry and pulse (normal, differential, and derivative) techniques at rotating disk electrodes, and by single sweep voltammetry at stationary disk electrodes; two different kinds of glassy carbon and one type of pyrolytic graphite were used to prepare the electrodes. The

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The avidin−biotin technology may be used successfully to build stable and spatially ordered assemblies of monomolecular enzyme layers on surfaces as illustrated with the example of glucose oxidase and glassy carbon electrodes. With ferrocene methanol as the cosubstrate, cyclic voltammetry allows a detailed analysis of the catalytic responses, thus providing a demonstration of the spatial order of the multilayer structure and an estimate of the average distance between monomolecular layers. The respective advantages of the avidin−biotin and antigen−antibody technologies are discussed.

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A method for fabricating submicrometer-sized gold electrodes of conical or spherical geometry is described. By generating an electric arc between an etched gold microwire and a tungsten counter electrode, the very end of the gold microwire can be melted and given an overall spherical or conical shape a few hundred nanometers in size. The whole wire is subsequently insulated via the cathodic deposition of electrophoretic paint. By applying a high-voltage pulse to the microwire, the film covering its very end can then be selectively removed, thus exposing a submicrometer-sized electrode surface of predefined geometry. The selective exposure of the preformed end of the microwire is demonstrated by cyclic voltammetry, scanning electron microscopy, and metal electrodeposition experiments. The electrophoretic paint coating provides a low-capacitance, robust insulating film allowing exploration of a very wide potential window in aqueous solution. The submicrometer-sized electrodes can easily be turned into probes suitable for combined scanning electrochemical-atomic force microscopy by bending and flattening the gold microwire so that the tip is borne by a flexible enough arm. The good agreement between theoretical and experimental scanning electrochemical microscopy approach curves thus obtained confirms that only the very end of the tip, of predefined geometry, is exposed to the solution.

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