Hydrophobic Moiety of Capsaicinoids Haptens Enhancing Antibody Performance in Immunoassay: Evidence from Computational Chemistry and Molecular Recognition

We previously found that the immune response to haptens is positively correlated with molecular hydrophobicity. The antibodies used in immunoassays for capsaicinoids (CPCs) in waste oil suffer from low affinity and loose recognition to structural analogues. To address this issue, four new haptens (hapten1–4), maximally exposing the hydrophobic alkane chain (noncommon moiety of CPCs), were designed and expected to produce antibodies with high affinity and accurate recognition to CPCs based upon our findings. The assumption was first evidenced by computational chemistry and animal immunization successively. Compared with four reported haptens (hapten5–8) that expose the hydrophilic vanillyl amide moiety (common structure of CPCs and other vanillin alkaloids), antisera from hapten1–4 showed an approximately 1000-fold increase in affinity and significantly improved recognition profiles for CPCs. The molecular recognition study showed that the high affinity of the antibody from new haptens mainly originated from hydrophobic forces. An indirect competitive enzyme-linked immunosorbent assay based on a monoclonal antibody from hapten1 was developed and exhibited limits of detection as low as 0.73–3.29 μg/kg for four CPCs in oils and with insignificant cross-reactivities for other eight vanillin alkaloids, which have been never achieved in previous reports.