A novel modified glassy carbon electrode (GCE) based on a new synthesized compound 1,4-phenylene-N,N'-bis (O,O-diphenylphoramidate) (PDPP), L-cysteine capped CdS quantum dots (CdS-QDs) and multi-walled carbon nanotubes (MWCNTs) was prepared. After studying the redox properties of the modified electrode by cyclic voltammetry, it was used as an electrochemical sensor for oxidation of captopril (CAP). Combination of CdS-QDs and MWCNTs with PDPP considerably improved the current response of the GCE towards electrocatalytic oxidation of CAP. Under hydrodynamic conditions (stirred solutions) at a fixed potential, oxidation current was proportional to the CAP concentration and calibration plot was linear over the concentration range of 0.05-90 mu M and detection limit was found to be 15 nM. The results of applying the proposed amperometric sensor for the determination of CAP in spiked urine and tablet were also encouraging. (C) 2014 Elsevier B.V. All rights reserved.