In this work, we synthesized water-dispersible cadmium sulfide quantum dots (CdS QDs) capped with 3-mercaptopropionic acid (MPA) in four sizes, namely 1,8,2.7, 3.2 and 3.7 nm using the hydrothermal method. The obtained CdS QDs were characterized using UV-vis spectra, fluorescence spectra, X-ray powder diffraction, and transmission electron microscopy. The electrochemiluminescence (ECL) of CdS QDs was investigated in. aqueous solution. With increasing the particle size of CdS QDs, not only ECL peak potentials but also ECL onset potentials were shifted positively accompanying the continuous increasing ECL intensity. Under the optimized conditions, the electrochemiluminescence of CdS QDs was used for dopamine (DA) detection linearly ranging from 8 pM to 20 nM with the detection limit of 3.6 pM (S/N = 3). Furthermore, the applicability of the proposed sensor was also applied to detect DA in human urine and serum. (C) 2016 Elsevier B.V. All rights reserved.