Application of aptamers as the sensing layers in biosensors offers several advantages for the detection of various analytes. Herein, an electrochemical label - free biosensor for dopamine (DA) was developed with the use of 57- mer DNA aptamer. The proposed aptasensor operates via specific interaction between dopamine and aptamer sequence tethered to the gold disk electrode via thiol group. DA concentration was determined without use of any external redox indicator and the dopamine oxidation current serves as the analytical signal. Electrodes modified with DNA aptamer show selectivity toward dopamine within micromolar range with the lower detection limit of 26.8 mu mol.L-1. The developed assay exhibits minor response in the presence of various interferents and its utility was tested in sample of diluted serum. Furthermore, the performance of proposed sensor was improved with LOD of 3.36 mu mol.L-1 and the range of linear response from 5 to 75 mu mol.L-1 by utilization of DNA aptamer/AuNP/reduced graphene oxide - modified glassy carbon electrode. (C) 2015 The Electrochemical Society. All rights reserved.