A similar to 13 mum diameter x 8 mum deep cavity with integrated electrodes was used for redox cycling in ultrasmall volumes ( similar to 1 nl) to selectively detect species that undergo reversible electron transfer reactions at electrodes in the presence of species that do not. Better sensitivities were obtained when the gold recessed microdisk (RMD), located at the bottom of the cavity, served as generator electrode and the gold tubular nanoband (TNB), located 4 mum away from the RMD and circling the cavity's wall, served its collector electrode, than for the reverse assignment. A gold electrode at the rim was the pseudoreference/auxiliary electrode. The signal at the collector electrode gave better detection limits than the amplified signal at the generator electrode for solutions of hexaamineruthenium(III) chloride and of dopamine, because charging current and faradaic current from interferents (e.g. oxygen and ascorbic acid) that undergo irreversible reactions were eliminated. The present work contrasts with other electrochemical detection methods for dopamine that require fast scan electronics or anionic coatings. It also contrasts with previously reported dopamine measurements that used redox cycling with larger working electrodes, external reference and auxiliary electrodes, and larger volumes. The detection limit for dopamine in the microcavity was 2 muM. By changing generator-collector spacings, the required performance at physiological concentrations should be possible. (C) 2003 Elsevier Ltd. All rights reserved.