Development of immunoassays for the detection of sulfamethazine in swine urine

The use of sulfonamides, such as sulfamethazine (SM2), in pig production is recognized as a public health risk as it inevitably results in sulfamethazine residues in pork. This study is aimed at establishing rapid, simple, reliable methods, with both sensitivity and specificity, for detecting sulfamethazine residues. For this purpose, monoclonal antibodies against sulfamethazine were prepared and characterized. No cross-reaction of the monoclonal antibodies was identified with other sulfonamides or analytes. Based on the competitive immunoassay principle, an indirect competitive ELISA kit (SM2 kit) and a rapid detection strip for detecting sulfamethazine residues were developed using monoclonal antibodies and the colloidal gold technique. The indirect competitive ELISA kit and the strip assay could be performed within 2 h and 5-10 min, respectively. The results showed that the detection limits were 1 ng ml-1 for the indirect competitive ELISA kit and 8 ng ml-1 with the unaided eye and 1 ng ml-1 with the strip reader for the rapid strip assay. Comparing the HPLC method with the SM2-kit or the strip in pig urine spiked with standards of SM2, the difference was 4.6% for SM2-kit and 4.3% for the strip. The two methods are suitable for the rapid screening of sulfamethazine residues in swine urine. Experimental data revealed that the two methods, especially the strip, proved to be sensitive, specific, rapid and easy to use for the quantitative, semi-quantitative or qualitative detection of SM2 residues in swine urine.