Electroanalysis of dopamine and NADH at conductive diamond electrodes

Highly boron-doped diamond thin-film electrodes were examined for various p ossible applications in electroanalysis. Electrochemical oxidation of dopam ine and NADH was investigated using cyclic voltammetry and chronoamperometr y. Comparison experiments were performed using glassy carbon electrodes. An odically treated diamond electrodes made it possible to determine dopamine selectively with high sensitivity in the presence of a large excess of asco rbic acid in acidic media. A detection limit of 50 nM was obtained using ch ronoamperometry. The treated electrodes were found to be stable for several months. Electrochemical oxidation of NADH was carried out at as-deposited diamond electrodes, with which very stable and reproducible cyclic voltammo grams for NADH oxidation were obtained, unlike glassy carbon, at which a si gnificant positive shift (similar to 200 mV) in the peak potential was obse rved within 1 h. The amperometric detection limit was found to be similar t o 10 nM. Interference of ascorbic acid was minimal using untreated electrod es when the concentration of ascorbic acid was comparable to the NADH conce ntration. Diamond microelectrodes small enough to consist of only one or tw o high quality microcrystals were fabricated in order to compare the electr ochemical behavior with that of polycrystalline thin film electrodes, which contain large numbers of grain boundaries, at which non-diamond (sp(2)) ca rbon can exist. This work demonstrates the potential of diamond electrodes for electroanalytical applications. (C) 1999 Elsevier Science S.A. All righ ts reserved.