Reusable ring-like Fe3O4/Au nanozymes with enhanced peroxidase-like activities for colorimetric-SERS dual-mode sensing of biomolecules in human blood

Peroxidase-like nanozymes have led to important progress in biosensing, but most of nanozyme sensing systems are currently established by a single-signal output mode, which is susceptible to environmental and operational factors. Thus construction of a dual-signal output nanozyme sensing system is essential for obtaining reliable and robust performance. In this study, a novel peroxidase mimicking nanozyme was developed by decorating magnetic ring-like Fe3O4 with gold nanoparticles (R-Fe3O4/Au) for the colorimetric and surface-enhanced Raman scattering (SERS) dual-mode detection of biomolecules in human serum. The R-Fe3O4/Au nanozymes served as mimetic peroxidase which can catalyze the oxidation of colorless 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide, and concomitantly as SERS substrates for detecting the Raman signals of oxidized products, providing an effective approach to investigate the reaction kinetics of enzymes. Based on the redox reactions, the nanozymes achieved colorimetric-SERS dual-mode sensing of glutathione (GSH) and cholesterol with detection limits as low as 0.10 μM and 0.08 μM, respectively. Furthermore, the nanozymes enabled rapid detection of GSH and cholesterol in serum without any complicated sample pretreatment. The R-Fe3O4/Au catalyst still displayed excellent peroxidase activity even after repeated use for 5 times. The proposed colorimetric-SERS dual-mode sensors exhibited good accuracy and reproducibility, which provides a new avenue for exploiting multifunctional sensors and has a great application prospect in biosensing.