Inner filter effect-based homogeneous immunoassay for rapid detection of imidacloprid residue in environmental and food samples

This paper reports a novel and sensitive homogeneous immunoassay for rapid detection of imidacloprid residue in environmental and food samples. The assay signal was originated from inner filter effect (IFE) between upconversion nanoparticles (UCNPs) and gold nanoparticles (AuNPs). UCNPs (energy donor) were coupled to the antibody against imidacloprid, and AuNPs (energy acceptor) were used to label the antigen of imidacloprid. The competitive immunoreaction occurred between imidacloprid and antigen-AuNPs binding to antibody-UCNPs. The assay system, sensitivity, selectivity , accuracy, and reliability were investigated. Under the optimal assay condition, the limit of detection for imidacloprid was 0.79   ng/mL and the concentration recovering 50% saturation of the signal (SC 50 ) was 18.7   ng/mL. The linear detection range (SC 10 to SC 90 ) was 1.39–335.81   ng/mL. Furthermore, the proposed method was successfully applied to determine imidacloprid in spiked water, Chinese cabbage, and honey samples, giving recoveries in the range of 78.1–97.9%. Through the blind sample tests, the IFE-based immunoassay demonstrated good correlation with ultra-performance liquid chromatography-tandem mass spectrometry (R 2 = 0.9866). Therefore, the new one-step immunoassay can be used as a promising tool for rapid detection of imidacloprid in field of environment and food safety.