A promising electrochemical sensor was developed through electrodepositing copper nanoparticles (CuNPs) on overoxidized poly(3-amino-5-mercapto-1,2,4-triazole) (p-TA(OX)) film modified glassy carbon electrode (GCE). The composite electrode exhibits excellent selectivity and sensitivity towards ascorbic acid (AA), dopamine (DA), uric acid (UA) and tryptophan (Trp). Amino and thiol groups exposed to the p-TA(OX) layer are helpful for the electrodeposition of CuNPs. The combination of CuNPs and p-TA(OX) endows the sensor with large surface area, good biological compatibility, electrical conductivity and stability, and flexible and controllable electrodeposition process. The calibration curves for AA, DA, UA and Trp were obtained in the range of 240.0-750.0 mu M, 0.6-21.6 mu M, 4.0-103.0 mu M and 4.0-144.0 mu M with detection limits (S/N = 3) of 5.0 mu M, 0.03 mu M, 0.16 mu M and 0.16 mu M, respectively. In addition, the analytical performance of this sensor has been evaluated for simultaneous detection of AA, DA, UA and Trp in the urine and serum samples. (C) 2015 Published by Elsevier B.V.