Nanoscale Synergetic Effects on Ag-Hyperbolic Metamaterial Substrate for Photoinduced Enhanced Raman Spectroscopy with Ultra-Sensitivity and Reusability

Multilayer hyperbolic metamaterials (HMM) based SERS substrates have received special consideration owing to the support of different propagating modes such as surface plasmonic polaritons (SPP) and bulk plasmon polaritons (BPP). However, due to its weak electric field enhancement, the SPP resonance has hardly originated in the periodic stack of metal and dielectric layers.The current study introduces an innovative 3D plasmonic structure comprising silver nanoparticles (AgNPs) and HMM (4 periods of Au/TiO₂) to enable highly sensitive and reliable photo-induced-enhanced Raman spectroscopy (PIERS). The use of this hybrid substrate results in an approximate 50-fold enhancement compared to standard surface-enhanced Raman spectroscopy, marking the most substantial PIERS enhancement achieved to date. Moreover, beyond the enhanced Raman signal, the hybrid substrate offers heightened detection sensitivity, possibly owing to its capability for activation with remarkably low UV irradiation and extended relaxation times (prolonged measurement durations). Our research indicates that the localized surface plasmon resonance (LSPR) of silver nanoparticles stimulates SPP, resulting in the creation of intense hot spot zones within the nanogap areas atop the HMM structure. Furthermore, the hybrid substrate showcases exceptional photocatalytic degradation of analytes, enabling its reuse for up to 15 cycles without any decline in PIERS activity. The suggested SERS structure demonstrates the capability for precise thiram quantitative detection, achieving sensitivity limits as low as 10^-7 M. This potential holds considerable promise in meeting fundamental requirements for environmental conservation and ensuring food safety.