Au-Ag@MnO2 NPs with label-free SERS activity and plasmon-enhanced electroreduction activity for dual-mode sensing of uric acid

Dual-mode detection nanotags with non-interference sensing signals had great potential to overcome the limitations of individual sensors, such as narrow monitoring range and inaccurate detection results. Herein, Au-Ag@MnO2 nanoparticles (NPs) with inherent surface-enhanced Raman spectroscopy (SERS) activity and plasmon-enhanced electroreduction (ER) signals were first reported. 2-mercaptobenzoimidazole-5-carboxylic acid (MBIA) mainly modulated the growth of Ag component and also endowed Au-Ag NPs with intrinsic SERS signals, thereby eliminating the need for additional modifications with SERS reporters. The deposition of MnO2 shell on Au-Ag NPs weakened the SERS signals but displayed two ER peaks at 0.5 V and 0.1 V, owing to the ER process of Mn4+ and Ag+, respectively. The peak at 0.5 V was amplified 1.23 times under light exciting, owing to the proposed plasmon-enhanced ER principle. H2O2 triggered the conversion of MnO2 to Mn2+ and exposed the Au-Ag NPs, resulting in “turn on” SERS signals and “turn off” ratiometric electrochemical responses. SERS-active and electroactive Au-Ag@MnO2 NPs achieved dual-mode detection of uric acid with urate oxidase (UOX) as catalysts. Rationally designed plasmonic metal-semiconductor heterogeneous nanocomposites may generate multiple-mode optical and electrochemical signals for accurate and quantitative detection applications.