Coupling Au-loaded magnetic frameworks to photonic crystal for the improvement of photothermal heating effect in SERS

The combination of plasmonic metals and photonic crystal (PC) structure is considered to have potential for further enhancement of the surface-enhanced Raman scattering (SERS) effect in comparison with conventional metal SERS substrates. Many studies have suggested that SERS signals probably suffer from an often-neglected effect of strong surface plasmon resonance (SPR)-induced photothermal heating during SERS detection. Herein, we have discovered that the photothermal heating problem arises in a traditional hybrid substrate that is prepared by doping plasmonic Au nanoparticles (NPs) into the voids of an opal PC (Au-PC). This happens mainly because excess Au agglomerates formed by non-uniformly distributed Au NPs can cause a strong SPR effect under laser illumination. To fully address this issue, we have employed an improved hybrid substrate that is fabricated by substituting Au NPs in Au-PC with an Au-loaded magnetic framework (AuMF). The AuMF can effectively prevent the aggregation of Au NPs and ensure sufficient hot spots for SERS. This novel substrate prepared by doping AuMFs into a PC (AuMF-PC) was free of strong photothermal heating and showed high SERS intensity and reproducibility of the SERS signal compared with Au-PC. For practical applications, we have demonstrated AuMF-PC as an appropriate candidate for the SERS assay of the trace thiol pesticide thiram, and it enables recycling and reuse to achieve low cost.