Gold (Au) nanoparticles immobilized on an amine-terminated self-assembled monolayer (SAM) on a polycrystalline Au electrode were successfully used for the selective determination of dopamine (DA) in the presence of ascorbate (AA). Well-separated voltammetric peaks were observed for DA and AA at the nano-Au electrode (Au nanoparticle-immobilized electrode). The oxidation potential of AA is shifted to less positive potential due to the high catalytic activity of Au nanoparticle. The reversibility of the electrode reaction of DA is significantly improved at the nano-Au electrode, which results in a large increase in the square-wave voltammetric peak current with a detection limit of 0.13 muM. The coexistence of a large excess of AA does not interfere with the voltammetric sensing of DA. The nano-Au electrode shows excellent sensitivity, good selectivity and antifouling properties. (C) 2003 Elsevier Science B.V. All rights reserved.