Gold clusters have been electrodeposited on a boron-doped diamond (131313) electrode by scanning the potential from 0.7 V to 0.0 V (vs. 3 M KCl-Ag/AgCl reference) in a solution of 0.5 mM KAuCl4 and 1.0 M KCl. The cluster-modified diamond (An/BDD) electrode has been used to investigate the oxidative properties of dopamine (DA) and ascorbate (AA). The modified diamond electrode shows a higher activity for DA oxidation than AA; the oxidation potential of DA shifted to a less-positive potential (0.11 V) than that of AA, which oxidized at 0.26 V, and DA possesses a much higher peak current than that of AA. The reversibility of the electrode reaction with DA is significantly improved at the Au/BDD electrode, which results in a large increase in the square-wave voltammetric peak current, with a detection limit of 0.1 mu M in the presence of a large excess of AA. The Au/BDD electrode shows excellent sensitivity and good selectivity for DA detection. A self-assembled monolayer (SAM) of mercaptoacetic acid on the Au clusters was used to provide an antifouling effect as the negative CO2-groups repulse negative ascorbate and attract positive dopamine in pH7.4 buffer. After pre-absorption, the SAM/Au/BDD electrode could detect 1.0 nM DA in a linear range from 10 nM to 10 mu M in the presence of 10(-4) M AA.