Multicolor visual screening of total dithiocarbamate pesticides in foods based on sulfydryl-mediated growth of gold nanobipyramids.

Dithiocarbamates (DTCs) pesticides were extensively used as fungicides in a variety of crops during their growth, storage and shipment. The DTCs residue in foods will seriously harm human health. In this study, a novel multicolor colorimetric sensor was developed for visual screening of total DTCs (total of ziram, thiram and zineb) based on sulfhydryl-mediated growth of gold nanobipyramids (AuNBPs). We demonstrated that DTCs can absorb on AuNBPs seed's surface via the formation of Au-S bonds and thus impede the 8-hydroxyquinoline (8-HQ)-promoted AuNBPs growth, which generates DTCs concentration-corresponding color changes. The developed sensor has vivid color changes, short analysis time, higher sensitivity and excellent specificity. It can be used to detect as low as 50 nM of total DTCs by bare eye observation and 17-18 nM of total DTCs by UV-visible spectrometry. By using the multicolor sensor, we have successfully screened total DTCs in apple and black tea by bare eye observation, and detected total DTCs in apple and black tea by UV-visible spectrometry with a recovery of 90%-104% and a relative standard deviation (RSD, n = 5) < 5%. The results obtained with our method consisted well with those obtained with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS), verifying that our method had good accuracy and reliability. Especially, the visual detection limit of our method is much lower than the maximum residue limit of total DTCs in vegetable and fruits. All above features make our sensor a promising method for rapid on-site screening of total DTCs in vegetable and fruits by only bare eye observation.