Plasmonic AgNPs reinforced flexible hydrogel Surface-Enhanced Raman scattering (SERS) sensor for in-situ detection of curved samples

In-situ detection of analytes on curved surfaces is a persistent and great challenge in the application of SERS technique. A hydrogel-based flexible SERS substrate demonstrates a unique charm for providing close contact to the real-sample surface but limited by its weak enhancement capability in the quantitative analysis. Herein, we report a reinforced hydrogel by reduction of plasmonic silver nanoparticles (AgNPs) on a PNIPAM membrane with the aid of polyvinylpyrrolidone (PVP) surfactant. The modification of AgNPs on PNIPAM endows the AgNPs/PNIPAM composite hydrogel with good mechanical properties and reinforced swelling property. Moreover, the AgNPs/PNIPAM hydrogel-based SERS sensor exhibits an enhanced SERS sensitivity as well as improved signal uniformity (RSD <10 %), and the detection concentration for pesticide molecules can be down to 10-9 M. Due to the fingerprint feature of SERS, multicomponent detection of pesticide mixtures was readily realized. In addition, the flexible AgNPs/PNIPAM hydrogel was successfully applied to the curved apple surface for SERS detection. Notably, it is capable of achieving qualitative and quantitative analyses of different pesticides, which has lower analytical concentrations than European Union (EU) standards, indicating the potential applications in rapid in-situ pesticide analysis.