A novel SERS-based rapid and sensitive assay for methidathion detection in various fruits

This study establishes a sensitive and facile method for trace detection of methidathion (MTDT) by using spherical Ag nanoparticles ( Ag NPs) based on surface enhanced Raman scatting (SERS). During detection, MTDT was rapidly alkaline hydrolyzed through S(N)2 substitution reaction and generated a thiadiazolin derivative with a more stronger Raman activity. After removing hydroxide ions from the solution, a limit of detection (LOD) as low as 0.33 ppb was achieved, which is two orders of magnitude below as compared to the non-hydrolysis group. Base on a self-developed and fast (10 min) pre-treatment method, MTDT was successfully detected in six kinds of fruit. The detection limits were ranged from 5-15 ppb, which were much lower than the maximum residue limit (MRL) required by China, US and the EU. Moreover, multivariate analysis (MVA) method was used for quantitative analysis in apple spiked samples, compared with univariate analysis (UVA), a higher determination coefficient (R-2 = 0.9331) and a better dynamic range (10 ppb-5 ppm) were obtained. The major aim of this work is to provide an operational, fast and sensitive method to specifically detect the MTDT pesticide in real agricultural samples.