An
antibody with broad specificity and principally depending on
hapten structure and size is a key reagent for developing a class-selective
immunoassay. In the present study, three new generic haptens
of antibacterial synergists (ASGs) were proposed using trimethoprim
as the starting molecule. These haptens contained carboxyl groups
on the meta position of trimethoxybenzene for
conjugating to protein, while, the common moiety of ASGs, i.e., diaminopyrimidine,
was intentionally and maximally exposed to the immune system in animals
in order to induce antibodies with broad specificity against ASGs.
Five monoclonal antibodies (mAbs) were finally obtained, and 5C4 from
the hapten with a short spacer arm, named Hapten A, showed not only
uniform broad specificity but also high affinity to all five ASGs.
We further determined the possible recognition mechanism of mAbs in
terms of conformational and electronic aspects. An indirect competitive
ELISA (icELISA)-based 5C4 was established and exhibited IC50 values of 0.067–0.139 μg L–1 with
cross-reactivity of 48.2%–418.7% for the five ASGs in buffer
under optimal conditions. The calculated limits of detection of the
icELISA for chicken and milk were 0.06–0.8 μg kg–1 and 0.05–0.6 μg L–1, respectively. The recoveries in spiked chicken and milk samples
were 75.2%–101.4% with a coefficient of variation less than
14.3%. In summary, we have developed, for the first time, a rapid
and reliable icELISA for ASGs with significantly improved sensitivity
and class selectivity.