A highly selective and sensitive electrochemical method, based on a poly(thionine)-modified glassy carbon electrode (PTH-GCE), was developed for the determination of dopamine (DA). The modified electrode was characterized by electrochemical techniques and an atomic force microscope (AFM). The modified GCE exhibited catalytic behavior towards the oxidation of DA in 0.1 M pH 7.0 phosphate buffer solution (PBS). In differential pulse voltammetry (DPV) measurements, the oxidation peak potential of ascorbic acid (AA), uric acid (UA) and serotonin (5-HT) overlapped with that of DA at the bare GCE. However, the oxidation peak of 5-HT was separated from that of DA at the PTH-GCE while the oxidation of AA and UA were suppressed at the same time. The peak potential separation of ca. 0.2 V was large enough for selective determination of DA from the interference of 5-HT. A linear range of 5.0-35.0 mu M and a detection limit (S/N = 3) of 0.2 mu M were obtained for DA detection in PBS (pH 7.0). This approach provides a simple and easy method to detect DA selectively from the interferences of AA, UA and 5-HT. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3576131] All rights reserved.