Improved SERS Performance on Ag-Coated Amorphous TiO2 Random Nanocavities by the Enhanced Light–Matter Coupling Effect

Flexible surface-enhanced Raman spectroscopy (SERS) substrates have garnered more and more attention due to their noninvasive sample collection ability. However, the improvement of SERS performance gradually reaches a bottleneck with numerous studies on exploration of active materials. In this study, we constructed an Ag@TiO2@cotton SERS substrate with randomly distributed TiO2 nanocavities, which can generate a strong coupling cavity mode, thus dramatically enhancing SERS activities. The prepared SERS substrates demonstrate high detection sensitivity, with a limit of 10–10 M for MB solution, an impressive enhancement factor (EF) of 2.7 × 108, excellent signal reproducibility, and remarkable stability. Furthermore, the proposed material allows the sensitive detection of MG with a limit of 1.0 × 10–10 M through a wiping fish collection method. These flexible Ag@TiO2@cotton substrates expand the range of available SERS substrates, and their easy fabrication method and long-term sensitivity hold promise for the trace analysis of harmful substances.