A neotype electrochemical sensor based on a three-dimensional nanoporous gold (3D-NPG) electrode decorated with ultra-thin platinum nanoparticles (Pt NPs) was fabricated for high-performance electrocatalysis and sensitive determination of hydrogen peroxide (H2O2) released from pheochromocytoma (PC12) cells. The monodisperse Pt–Au bimetallic nanoporous (Pt–Au–BNP) electrode prepared by cyclic voltammetry electrodepositing monolayer Pt NPs on the surface of the 3D-NPG electrode was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy-dispersive spectroscopy (EDS). Amperometric response for H2O2 measurement was chosen at an applied potential of − 0.4 V. Upon optimal conditions, the wide linear range for the amperometric determination of H2O2 was from 0.05 μM to 7.37 mM, with a limit of detection (S/N = 3) of 1.5 × 10−8 mol/L and a high sensitivity of 1.125 μA μM−1 cm−2, certifying the large electrocatalytic action of the Pt–Au–BNP electrode. The proposed sensor has been successfully applied to the dynamic determination of H2O2 released from PC12 cells (from which the H2O2 generated by each cell was about 52.5 amol) with negligible interference. Thus, the proposed new electrochemical sensor displays potential applications for the dynamic, real-time monitoring of key small molecules secreted by living cells, further deepening the understanding of cell behavior stimulated by foreign materials. Graphical Abstract.