Facile synthesis of graphene-coupled silver nanostructure-based hybrid SERS for trace-level SERS detection of thiram

The increasing need for reliable and trace-level detection of hazardous agrochemicals stimulated the development of hybrid surface-enhanced Raman spectroscopy (SERS)-active substrates with improved sensitivity and selectivity. A single-step, facile growth process engineered for fabricating plasmonic silver nanostructures and its application for trace detection of thiram has been explored, and detailed experimental and finite-difference time-domain (FDTD) simulation has been investigated. The SERS measurement along with FDTD simulations identified the silver nanostructure with a particle size and inter-particle gap of ∼61 nm and ∼22 nm, respectively, as the optimal plasmonic structure demonstrating the highest plasmonic coupling, which further showed the limit of detection (LOD) of 10^-10 M for thiram with an enhancement factor (EF) of 4.25 × 10¹⁰. The coupling of graphene with optimal silver nanostructure exhibits a significant enhancement in the SERS signal compared with the bare silver nanostructure substrate, with about one order more increase in the EF due to the enhanced plasmonic coupling induced by the incorporation of graphene and understood from the FDTD analysis. Graphene, with its Fermi level possibly modulated and subsequently tuned to align with HOMO-LUMO levels of thiram could be responsible for improved plasmonic coupling and hence increased SERS performance.