Detection of salinomycin and lasalocid in chicken liver by icELISA based on functional bispecific single-chain antibody (scDb) and interpretation of molecular recognition mechanism

Salinomycin (SAL) and lasalocid (LAS) are widely used as ionophore antibiotics for coccidiosis control. However, their common use as feed additives has led to the occurrence of feed cross-contamination, which has toxic effects on non-target animals. There have been few reports on multiple-residue detection for SAL and LAS in recent years. In this study, two single-chain antibody fragments (scFvs) capable of specifically recognizing SAL and LAS were constructed. Using LAS-scFv and SAL-scFv as parent antibodies, a complete bispecific single-chain diabody (scDb) against both LAS and SAL was built using splicing by overlap extension polymerase chain reaction (SOE-PCR). In addition, the key amino acid sites and interaction energy of antibody variable regions for small-molecule recognition were preliminarily studied by homology modeling and molecular docking. Finally, IC50 values of 12.9 and 8.6 ng/mL, with a linear range of 6.9–24.0 and 4.7–16.0 ng/mL, were obtained for LAS-scFv and SAL-scFv, respectively. An indirect competitive enzyme-linked immunosorbent assay (icELISA) method was established using scDb to obtain an IC50 of 3.5 ng/mL for LAS and 4.1 ng/mL for SAL, which showed better sensitivity and specificity than those of the parent scFv antibodies. The recoveries of LAS and SAL in chicken liver were 89.2–92.7%(CV<4.7%) and 88.6–90.2% (CV<6.8%)), respectively.