Alkali hydrolysis and Lewis acids assisted enhancement based highly sensitive and quantitative detection of malathion in tea using SERS and multivariate analysis

This study establishes an incredibly simple method for trace detection of malathion (MLT) by using spherical Ag nanoparticles (Ag NPs) based on surface enhanced Raman scatting (SERS). MLT was rapidly hydrolyzed through β-elimination reaction under alkaline condition, then provided a favorable ionic environment for SERS detection by using Lewis acids (LAs), leading to a 305 times maximum additional enhancement, and a limit of detection (LOD) as low as 0.1 ppb was achieved. The different alkaline hydrolysis pathways of MLT and other dithiophosphate organophosphorus molecules was clarified, and the conversion of molecular binding states on nano-surface were determined. The method was successfully applied in various tea samples, a LOD as low as 0.05 ppm was obtained. Due to the complex variation of characteristic peaks intensity, multivariate analysis method was used for quantitative analysis and a high determination coefficient (R2 =0.9573) and good dynamic range of 0.1–5 ppm were obtained.