Fabrication and the highly sensitive SERS performance of Ag-decorated ZnO flower-like microrods for methidathion detection

Abstract

Methidathion (MD), a highly hazardous pesticide, poses a severe threat to public health and the environment. This study presents a highly sensitive and reproducible surface-enhanced Raman scattering (SERS) substrate for the detection of trace amounts of MD. The substrate consists of silver nanoparticles (Ag NPs) embedded along the edges of hexagonal zinc oxide (ZnO) flower-like microrods (FLM), fabricated via a two-step process, namely, hydrothermal and chemical reduction methods. The structural, morphological, and optical characteristics of the prepared heterostructure were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), EDX mapping, and UV-vis spectroscopy. The ZnO/Ag hybrid heterostructure exhibited superior SERS performance compared to the pure Ag and ZnO substrates. The SERS activity was systematically optimized by varying the Ag content, with ZnO/Ag4 demonstrating the highest enhancement factor (EF) of 1.1 × 10⁷, a limit of detection (LOD) of 0.2 ppm and a wide linear range (0.2–20 ppm). The optimized substrate retained good activity after six months of preservation, confirming the stability of the SERS substrate. The improved SERS performance is attributed to the combined electromagnetic and chemical enhancement mechanisms, including a high density of plasmonic hotspots and efficient charge transfer at the ZnO/Ag interface. Density functional theory (DFT) simulation was employed to gain a deeper understanding of the electronic and vibrational modes contributing to the SERS enhancement. This work demonstrates the potential of the ZnO/Ag hybrid as a robust and effective SERS platform for the detection of hazardous chemicals in real-world agricultural samples.