A ultrasensitive electrochemical biosensor was successfully constructed for the detection of Cd (II) based on nitrogen-doped reduced graphene oxide-persimmon tannin (PT-N-RGO) and gold nanoparticles (Au NPs) modified screen printing electrode (SPE). The structure and morphology of the prepared PT-N-RGO nanocomposite were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (TEM). And each step in the sensor preparation was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Au NPs as a material of modified electrode not only increased the effective surface area of the electrode, but also promoted the electron transfer during the redox reaction. The high specific surface area of PT-N-RGO composites further increased the electron transfer rate, thus improving the conductivity of the electrode and providing more binding sites for the subsequent capture of Cd (II). Under the optimized experimental conditions, the sensor exhibited good linearity in the range of 3.0~30 µg/L Cd (II) with a minimum detection limit of 0.46 µg/L. The sensor showed good selectivity, stability and reproducibility for the determination of Cd (II). The sensor was applied to the analysis of real water samples and the results were verified by inductively coupled plasma mass spectrometry (ICP-MS), and satisfactory results were obtained, providing a new idea for the effective determination of trace heavy metals in the environment.
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