Trace Detection of Deltamethrin via Au/Cu₂O/ZnO SERS Substrates with Multiple Heterojunctions

Organic pesticide residues accumulate in the human body through dietary consumption, presenting a significant health risk. Therefore, efficient and sensitive detection of these residues is crucial. Surface-enhanced Raman scattering (SERS), as a powerful non-destructive detection technology, has attracted more attention due to its exceptional sensitivity and versatility. This study presents a novel Au/Cu₂O/ZnO SERS substrate, synthesized through a multiple-cycle chemical adsorption plus reduction method, which exhibits exceptional sensitivity, stability, and repeatability. The substrate achieves a remarkable limit of detection (LOD) of 10^-13 M for Rhodamine 6G (R6G), with an impressive enhancement factor of approximately 3.8 × 10¹⁰. Notably, the substrate's efficacy was further demonstrated in the successful detection of deltamethrin with a LOD of 0.01 mg/L. The effects of ZnO, Cu₂O, and Au on the SERS performance of the substrate were clarified through a comprehensive analysis of the charge transfer mechanism. Experimental results demonstrate that the multiple heterojunctions within the ternary composite structure significantly facilitate the photo-induced charge transfer, thereby enhancing the SERS activity. This study demonstrates the potential of three-dimensional structures with multiple heterojunctions to significantly improve SERS performance and offers a novel strategy for designing noble metal/semiconductor SERS substrates characterized by dense hotspots and high charge transfer contributions.