In this work, the N doping together with Pd-Cu@Cu2O hybridization for graphene oxide was achieved by a combined process of hydrothermal treatment and chemical reduction, based on which a novel Pd-Cu@Cu2O cubes decorated N-doped reduced graphene oxide (Pd-Cu@Cu2O/N-RGO) hybrid was obtained. The synthesized Pd-Cu@Cu2O/N-RGO was detailedly characterized by various technologies. The results show that the low Pd loading Cu@Cu2O cubes with the sizes of 300-500 nm are well dispersed on N-RGO sheets, thereby avoiding the serious aggregation and maintaining a large electro-active surface area of the attained hybrid. Benefiting from the synergistic effect of the properties of Pd-Cu@Cu2O particles and N-RGO sheets, the Pd-Cu@Cu2O/N-RGO modified electrode exhibits remarkable electrocatalytic performance on the oxidation of tryptophan with the enhanced oxidation response and the lowered oxidation overpotential. Under the optimal conditions for the electrochemical detection of tryptophan, the constructed sensor displays a wide linear range (0.01-40.0 mM) and a low detection limit (1.9 nM), outperforming most of the reported hybrid-based sensors. The proposed sensor also features good selectivity, stability and reproducibility, which has been successfully applied for the detection of tryptophan in the urine and milk samples with satisfactory recoveries. All these results suggest that the Pd-Cu@Cu2O/N-RGO hybrid could be a promising and convenient material for the fabrication of high-performance electrochemical sensors. (c) 2017 Elsevier Ltd. All rights reserved.