A colorimetric paper-based sensor for toltrazuril and its metabolites in feed, chicken, and egg samples.

In this study, a sensitive monoclonal antibody (mAb) against toltrazuril (Tol) was developed based on a novel hapten. The 50% inhibitory concentrations (IC) of toltrazuril and its metabolites ranged from 2.19 ng/mL to 4.21 ng/mL. Based on this mAb, a colorimetric paper-based sensor was developed for the rapid screening of Tol and its metabolites in samples. The proposed assay has cutoff values of <20 μg/kg for Tol and 50 μg/kg for Tol sulfone when evaluated with the naked eye, and the results could be obtained in 15 min. Quantitative results were obtained with a strip scan reader, with limits of detection <2.60 μg/kg for Tol and its metabolites in real samples. The sensitivity of both qualitative and quantitative detection meets the European Union requirements. Therefore, this strip assay provides a useful tool for the on-site detection and rapid initial screening of Tol and its derivatives in feed, egg, and chicken samples.