The inherent redox activity of dopamine enables its direct electrochemical in vivo analysis ( Venton , B. J.; Wightman, M. R. Anal. Chem. 2003, 75, 414A). However, dopamine analysis is complicated by the interference from other electrochemically active endogenous compounds present in the brain, including dopamine precursors and metabolites and other neurotransmitters (NT). Here we report an electrochemical RNA aptamer-based biosensor for analysis of dopamine in the presence of other NT. The biosensor exploits a specific binding of dopamine by the RNA aptamer, immobilized at a cysteamine-modified Au electrode, and further electrochemical oxidation of dopamine. Specific recognition of dopamine by the aptamer allowed a selective amperometric detection of dopamine within the physiologically relevant 100 nM to 5 μM range in the presence of competitive concentrations of catechol, epinephrine, norepinephrine, 3,4-dihydroxy-phenylalanine (L-DOPA), 3,4-dihydroxyphenylacetic acid (DOPAC), methyldopamine, and tyramine, which gave negligible signals under conditions of experiments (electroanalysis at 0.185 V vs Ag/AgCl). The interference from ascorbic and uric acids was eliminated by application of a Nafion-coated membrane. The aptasensor response time was <1 s, and the sensitivity of analysis was 62 nA μM(-1) cm(-2). The proposed design of the aptasensor, based on electrostatic interactions between the positively charged cysteamine-modified electrode and the negatively charged aptamer, may be used as a general strategy not to restrict the conformational freedom and binding properties of surface-bound aptamers and, thus, be applicable for the development of other aptasensors.