Application of surface-enhanced Raman scattering in rapid detection of dithiocarbamate pesticide residues in foods

Abstract

Dithiocarbamates (DTCs) are a group of fungicides with various toxicities, and are widely used in agriculture. Currently, most of the official DTC detection methods cannot identify residues of individual DTCs, such as dimethyldithiocarbamates (DMDCs), ethylene-bis-dithiocarbamates (EBDCs) and propylene-bis-dithiocarbamates (PBDCs), on crops. Surface-enhanced Raman scattering (SERS) provides fingerprint recognition from the scattering spectra of molecular vibrations, and it has excellent potential as a primary qualitative screening tool. In this study, glancing angle deposition (GLAD) was used to fabricate SERS substrates with Ag@Au alloyed nanorods to provide cost-effective and rapid detection, and an optimal procedure for extracting DTC residues on the surface of crops was proposed. This study verified that under ordinary Raman spectroscopy conditions (excitation light, 785 nm; power, 20 mW; and integration, 3 min), extraction with tepid water and the addition of 0.1% sodium chloride can enable the detection of thiram (a DMDC), propineb (a PBDC) and mancozeb (an EBDC) on crops at trace concentrations of 0.05, 0.1 and 0.2 ppm, respectively, even on crops containing high levels of endogenous sulfides, such as cauliflower and white radish. Using the developed SERS-active substrate, qualitative and semi-quantitative results can be obtained by employing the specific characteristic peaks of the Raman scattering patterns to distinguish three types of DTCs. The method proposed in this study offers the advantages of simple operation, few consumables, high safety, and no interference from the matrix. Hence, this study provides an auxiliary approach for DTC detection.