Fabrication of Ag–Cu2O/Reduced Graphene Oxide Nanocomposites as Surface-Enhanced Raman Scattering Substrates for in Situ Monitoring of Peroxidase-Like Catalytic Reaction and Biosensing

Highly sensitive biosensors are essential in medical diagnostics, especially for monitoring the state of an individual’s disease. An ideal way to achieve this objective is to analyze human sweat secretions by noninvasive monitoring. Due to low concentrations of target analytes in human secretions, fabrication of ultrasensitive detection devices is a great challenge. In this work, Ag–Cu2O/reduced graphene oxide (rGO) nanocomposites were prepared by a facile two-step in situ reduction procedure at room temperature. Ag–Cu2O/rGO nanocomposites possess intrinsic peroxidase-like activity and rapidly catalyze oxidation of the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H2O2. On the basis of the excellent SERS properties and high peroxidase-like activity of the Ag–Cu2O/rGO nanocomposites, the catalytic oxidation of TMB can be monitored by SERS. This approach can detect H2O2 and glucose with high sensitivity and distinguish between diabetic and normal individuals using glucose levels in fingerprints. Our work provides direction for designing other SERS substrates with high catalytic activity and the potential for application in biosensing, forensic investigation, and medical diagnostics.