Virtual mutation and directional evolution of anti-amoxicillin ScFv antibody for immunoassay of penicillins in milk.

In this study, an anti-amoxicillin single chain variable fragment (ScFv) antibody was evolved by directional mutagenesis of a contact amino acid residue based on the analysis of virtual mutation. Comparison with its parental ScFv, the mutant showed highly improved affinity for 11 penicillins with up to 6-folds increased sensitivity. Then, its recognition mechanisms for the 11 drugs were studied by using molecular docking. Results showed that the mutant-penicillins intermolecular forces increased and the total binding energies decreased dramatically, which were responsible for the improvement of antibody sensitivity. The ScFv mutant was used to develop an indirect competitive enzyme linked immunosorbent assay for determination of the 11 drugs in milk. The limits of detection were in the range of 0.2-3.0 ng/mL, the crossreactivities were in the range of 31%-132%, and the recoveries from standards fortified blank milk were in the range of 65.7%-92.4%. This is the first study reporting the directional evolution of a ScFv antibody based on virtual mutation and the use of ScFv antibody for determination of penicillins in foods of animal origin.