Development and identification of monoclonal antibodies against ractopamine.

Ractopamine was reacted with two carrier proteins, human serum albumin and bovine thyroglobulin, as immunogen and coating antigen, respectively. Using a conventional immunization protocol, we generated a stable murine monoclonal antibody toward ractopamine, which had high affinities. The clone was found to be of IgG(2a) subclass with kappa light chain. An indirect competitive enzyme-linked immunosorbent assay for the determination of ractopamine has been optimized and characterized. The sensitivity, estimated as the IC(50) value, was 21.25 ng/mL, with a practical working range between 2.9 and 450 ng/mL. The limit of detection was 1.5 ng/mL. Moreover, other phenethanolamine beta-agonists showed low cross-reactivity with the monoclonal antibody. In addition, the indirect competitive enzyme-linked immunosorbent assay for the detection of ractopamine in animal feed was also developed using this antibody.