Computer-Aided Rational Hapten Design of Mepiquat Chloride: High-Affinity Antibody and Sensitive Immunoassay for Food and Environmental Samples

Mepiquat chloride (MQ) residues threaten human health and ecological safety, requiring rapid and sensitive monitoring. In this study, five haptens were designed for poorly immunogenic MQ, and MQ-H4/MQ-H5 was identified as the optimal pair via computer-aided analysis and serum validation, generating MQ mAb-5H2 with high affinity and specificity. Based on this mAb, a gold nanoparticle-based lateral-flow immunochromatographic assay was developed for MQ on-site screening, with the calculated limits of detection of 0.034, 0.049, and 0.016 mg/kg in potato, wheat, and soil, respectively. The reliability and accuracy of the method were verified through spiked recovery experiments, showing recoveries from 95.2 to 105.7% and a coefficient of variation of 1.6-7.1%, consistent with the results of high-performance liquid chromatography-mass spectrometry, providing a practical and reliable tool for MQ monitoring and a hapten-driven strategy for high-performance antibody generation and sensitive immunoassays targeting other quaternary ammonium pesticides.