Monoclonal antibody-based fluorescence polarisation immunoassay for nifursol in feed

Novel tracers were designed and then used to develop a rapid, specific and sensitive fluorescence polarisation immunoassay (FPIA) method to detect nifursol in feed. The 3-((2-(2-hydroxy-3,5-dinitrobenzoyl)hydrazono)methyl)benzoic acid was used for the production of immunogen and 3,5-dinitrosalicylic acid was used for synthesis of fluorescein-labelled tracer. Based on monoclonal antibody and tracer, an optimised FPIA method was established with IC50 of 5.0 ng mL-1, and low cross-reactivity with other nitrofurans (<0.05%). FPIA provides a suitable means for screening of a large number of samples. The limits of detection calculated from the analysis of 20 known negative feed samples (pig feed, chicken feed and fish feed) were 0.4-0.8 ng g-1 (mean + 3 SD). Recoveries of nifursol fortified ranged from 85.0 to 95.0%. The coefficients of variation were less than 10%.