Rice straw-derived carbon based nanozyme sensor: Application of identifying human urine xanthine content and study of active sites

Development of biomass-based nanozyme sensors is an important measure to improve the catalytic performance of nanozymes and achieve efficient resource utilization. In this study, rice straw is used as raw material and modified by MgCl2 to synthesize biomass carbon dots nanozyme (Mg,Cl-rsCDs) with peroxidase activity. The oxygenous groups inherent in rice straw play a positive role in improving the catalytic activity. Compared with natural enzymes, Mg,Cl-rsCDs have the advantages of stronger stability, wider applicable temperature range and better catalytic kinetic behavior. The active sites and enzyme-like catalytic mechanism of Mg,Cl-rsCDs are studied by density functional theory and free radical recognition techniques. We consider that the modification of MgCl2 changes the electroneutrality of the original carbon skeleton and promotes the synergistic effect of functional groups to generate active sites. Relying on the peroxidase activity of Mg,Cl-rsCDs, a biomass nanozyme-natural enzyme cascade catalytic system is constructed and used to detect the content of xanthine in human urine. The system has excellent linear range (0.2–80 μM), low detection limit (0.08 μM) and satisfactory reproducibility (RSD = 2.3–4.8%). This work provides a new strategy for production of biomass nanozymes and deep utilization of straw, which is of great significance for biosensing and resource engineering.