Comparison of biosensor, microbiological, immunochemical, and physical methods for detection of sulfamethazine residues in raw milk

A biosensor assay based on biospecific interaction analysis (BIA) was compared with already existing methods for detection of sulphamethazine (SMZ) residues in milk. Microbial inhibitor and receptor assays, an enzyme-linked immunosorbent assay (ELISA), high-pressure liquid chromatography (HPLC), and BIA were used to analyze milk samples from SMZ-treated cows. The results of the commercially available tests (Delvotest SP Special, BR-test Blue Star, Charm II test) were in agreement with the claimed sensitivity of the respective assays. The agreement between the quantitative methods (ELISA, HPLC, BIA) varied. The microbial inhibitor assays and BIA were also used to screen 330 tanker milk samples. All samples were negative in the inhibitor tests, whereas the BIA indicated the occurrence of less than 0.9 micrograms of SMZ per kg of milk in 5 samples and 1.5 +/- 0.6 micrograms/kg in one sample. HPLC indicated the presence of SMZ in the latter sample, although the concentration was below the detection limit of the method. The advantages offered by the BIA: no sample preparation, high sensitivity, and rapid, fully automated analysis in real time make the technology an interesting alternative to existing screening methods within future food-quality control systems