Ultrasensitive quantitation of imidacloprid in vegetables by colloidal gold and time-resolved fluorescent nanobead traced lateral flow immunoassays.

• Colloidal gold and time-resolved fluorescent nanobead for immunoassay. • On-site quantitation of imidacloprid in vegetable by two lateral flow immunoassays. • Comparison of two tracers for assay sensitivity at optimizing conditions. • Lateral flow immunoassay is an alternative to enzyme-linked immunosorbent assay. Imidacloprid is a highly effective insecticide, but its potential hazards to the environment and ecosystems have limited its use in many regions. A fast and sensitive analytical method would aid monitoring imidacloprid residues. The monoclonal antibody 4D9, colloidal gold and time-resolved fluorescent nanobeads (CGN and TRFN, respectively) were applied to develop a lateral flow immunoassay (LFIA) for imidacloprid detection in the present work. Both the optimized TRFN-LFIA and CGN-LFIA had a similar limit of detection of approximately 0.02 ng/mL. Use of the portable optical scanner with the TRFN-LFIA or CGN-LFIA could quantitate concentrations of imidacloprid in vegetable as sensitively as the enzyme-linked immunosorbent assay (ELISA). The LFIAs quantitative results of imidacloprid in commercial Chinese leeks were verified by the liquid chromatography-mass spectrometry with a R 2 of 0.91. The LFIAs are portable and simple and thus could fully replace the ELISA for onsite quantitation of imidacloprid residues in vegetables. [ABSTRACT FROM AUTHOR]