▎ 摘　　要

A novel NH4+ voltammetric electrochemical biosensor was constructed by immobilizing glutamate dehydrogenase (GLDH)/Fe3O4/graphene (GR)/chitosan (CS) nanobiocomposite onto a glassy carbon electrode (GCE). On the GLDH/Fe3O4/GR/CS/GCE, GLDH catalyzed the reversible reaction, i.e., the reductive amination of alpha-ketoglutaric acid and the oxidative deamination of L-glutamate. The electrons produced in the enzymatic reactions were transferred to the surface of the electrode via the [Fe(CN)(6)](3-/4-) couple, which helped for the amplification of the electrochemical signal. The electrochemical detection of NH4+ was based on the fact that the enhanced response current was proportional to the NH4+ concentration. Owing to the combination of the advantages of the synergistic effects of Fe3O4 nanospheres, GR and CS, a promising platform for NH4+ sensing was provided. Under optimum conditions, the introduced biosensor had a linear range of 0.4-2.0 mu M for NH4+ with the detection and quantification limits of 0.08 and 0.27 mu M, respectively. Moreover, the biosensor exhibited good sensitivity and excellent reproducibility. It could retain 91.8% of its original response after two weeks of storage at 4 degrees C, suggesting satisfactory stability. Additionally, the proposed biosensor was successfully applied to detect NH4+ levels in PM2.5 samples, indicating its feasibility for application in NH4+ monitoring in the environmental fields.