▎ 摘　　要

Fe3O4-brominated graphene (Fe3O4-GBR) nanocomposites were synthesized via an in situ method using the precursors FeSO4 center dot 7H(2)O and GBR in different (1:1, 1:2, 2:1, 1:5, 1:10, 1:20, and 5:1) weight ratios at pH 11.5. The Fe3O4-GBR (1:5) nanocomposite in combination with H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB) showed swift and superior intrinsic peroxidase mimetic enzyme activity compared with the other Fe3O4-GBR composites, GBR and Fe3O4, as observed by colorimetry. It was characterized using high-resolution scanning electron microscopy (HRSEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD), and thermogravimetric analysis (TGA). Its catalytic activity was optimized by varying different parameters, and the optimum conditions for peroxidase mimetic activity were observed using 100 mu L Fe3O4-GBR (1 mg/mL), 50 mu L TMB (1 mg/mL), and 200 mu L H2O2(1 mM) in 400 mu L of acetate buffer of pH 2.3 at 30 degrees C temperature. Kinetic analysis has revealed the Michaelis-Menten kinetic behavior of peroxidase activity with Michaelis-Menten constants (K-m) and maximum initial velocities (V-max) of 0.082 mM and 14.1 nMs(-1) respectively, for H2O2 and 0.086 mM and 5.1 nMs(-1), respectively for TMB. The limit of detection and linear range were found to be 49.6 mu M and 100-880 mu M, respectively, for H2O2 and 41.9 mu M and 47.6-952.3 mu M, respectively, for cholesterol. On this basis, a simple, swift, sensitive, selective, and reproducible colorimetric assay to detect cholesterol levels in blood serum samples using Fe3O4-GBR nanocomposite has been developed. Thus, Fe3O4-GBR composite as compared to Fe3O4 and GBR has shown better peroxidase mimicking activity for biosensing.