Upconversion nanoparticles-based background-free selective fluorescence sensor developed for immunoassay of fipronil pesticide

In this study, high luminous efficiency, sensitive and specific fluorescent immunosensor was proposed for the detection of fipronil in spinach (cultivar: Spinacia oleracea L.), celery (cultivar: Apium graveolens L.) and pak-choi (cultivar: Brassica Chinensis L.) by employing the fluorescence resonance energy transfer (FRET). The background-free upconversion nanoparticles-antibodies (UCNPs-antibodies) and gold nanoparticles-antigens (AuNPs-antigens) were prepared, respectively. Fipronil competed with the fipronil whole antigens for the fipronil monoclonal antibodies active sites. The results indicated that the correlation between the concentration of fipronil and the fluorescence intensity had a high relevance (R 2  = 0.9987) in the range of 0.01-100.00 ppb. The average recovery was 95.95-137.07%. This method had great application potential in food safety monitoring and can provide a reference for the analysis of other small molecule pesticide residues.