Mn3O4–Au nanozymes as peroxidase mimic and the surface-enhanced Raman scattering nanosensor for the detection of hydrogen peroxide

The artificial enzyme-mimicking system using nanomaterials has attracted significant research interest in chemical and biological sensing for industrial and environmental applications. Mn3O4 nanostructure serves as an effective catalyst in oxidation and reduction reactions that mimic natural peroxidase enzymes. In this study, we synthesized Mn3O4–Au spindle nanocomposites (Mn3O4–Au SNCs) stabilized by L-cysteine using a simple hydrothermal reduction. The enzyme-mimicking peroxidase activity of these Mn3O4–Au SNCs with hydrogen peroxide (H2O2) was investigated in the presence of a chromogenic substrate, 3,3′,5,5′-tetramethylbenzidine that catalyzed reduction of H2O2 in water and milk giving rise to a blue color inferring the nanozyme activity of Mn3O4–Au SNCs. The exceptional enzyme-like catalytic activity of Mn3O4–Au SNC probes later proved to be excellent surface-enhanced Raman scattering (SERS) sensor nanoprobes for sensitive H2O2 detection over a wide concentration range from 0.005 to 10 μM. The developed Mn3O4–Au SERS sensor exhibited a lower detection limit (LoD) of 2 nM in water and 0.6 μM in spiked milk indicating sensitivity for H2O2 detection with excellent selectivity, reproducibility, and long-term stability. The developed Mn3O4–Au nanoprobes demonstrated unique combination of properties with visual and SERS methods for sensitively detecting H2O2 in food, overcoming limitations of existing H2O2 sensors. The developed SERS method using nanozymes potentially be extended to detecting a variety of other redox chemicals or explosives in industries, environments, and biomedical fields.