Determination of sulfamethazine in milk by biosensor immunoassay

A biosensor based on surface plasmon resonance (SPR) measurement was develo ped for use in an immunoassay for detection of sulfamethazine (SMZ) in milk , The biospecific surface was a carboxymethyl dextran-modified gold-surface sensor chip to which SMZ was covalently bound. The assay was based on inhi bition of the binding of polyclonal antibodies to immobilized SMZ by SMZ in the sample. The SPR response changed inversely in relation to the antibiot ic concentration in the sample. Calibration curves were constructed for SMZ in buffer and in milk at a concentration which included the maximum residu e limit (0 to 200 mu g/kg). The analysis time per sample varied from 8 to 3 0 min. Different flow rates and antibodies were modified alternatively duri ng the study to assess their influence on the performance of the assay. The active antibody concentration was calculated at approximately 1880 and 180 nM for the antibody anti-SMZ 1 and the antibody anti-SMZ 2, respectively. No cross-reactivity of antibodies with other antibiotics was found. Under o ptimal conditions, the detection limits in milk for SMZ were 8 and 1.7 mu g /kg, respectively, for antibody 1 and antibody 2, at a flow rate of 20 mu L /min.