In this report, graphene oxide–Fe3O4 magnetic nanocomposites were demonstrated to possess intrinsic peroxidase-like activity and enhanced affinity toward H2O2. The nanocomposites retain their magnetic properties and can be effectively separated by a magnet. Significantly, they were proved to be novel peroxidase mimetics which could quickly catalyze oxidation of the peroxidase substrate 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue-colored solution. Kinetic analysis indicates that the catalytic behavior is in accord with typical Michaelis–Menten kinetics and follows a ping-pong mechanism. On the basis of the high activity, the reaction provides a simple, sensitive and selective method for colorimetric detection of glucose in diabetic urine.
