Fluxapyroxad Haptens and Antibodies for Highly Sensitive Immunoanalysis of Food Samples

Fluxapyroxad is a new-generation carboxamide fungicide, with residues increasingly being found in food samples. Immunochemical assays have gained acceptance in food quality control as rapid, cost-effective, sensitive, and selective methods for large sample throughput and in situ applications. In the present study, immunoreagents to fluxapyroxad were obtained for the first time, and competitive immunoassays were developed for the sensitive and specific determination of fluxapyroxad residues in food samples. Two carboxyl-functionalized analogues of fluxapyroxad were prepared, and antibodies with IC₅₀ values in the low nanomolar range were generated from both haptens, though a dissimilar response was observed concerning specificity. A robust direct assay was set up, with a calibration curve exhibiting a limit of detection of 0.05 nM (0.02 μg/L). Limits of quantitation of 5 μg/L were obtained for peach, apple, and grape juices using samples diluted in water. The direct immunoassay was also successfully applied to the determination of fluxapyroxad in grapes from in-field treated grapevines.