Development of a one step strip test for the detection of (dihydro)streptomycin residues in raw milk

The one step strip test described is a competitive immunoassay in which the detector reagent consists of colloidal gold particles coated with affinity purified monoclonal anti-(dihydro)streptomycin antibodies. the capture reagent in the assay is a streptomycin-bovine serum albumin conjugate which is immobilised on the lateral flow membrane of the test device. In the test procedure, three drops of raw milk are brought into the sample well of the test device and allowed to migrate over the membrane. The more analyte present in the sample, the more effectively it will compete with the streptomycin immobilised on the membrane for binding to the limited amount of antibodies of the detector reagent. A sufficient amount of (dihydro)streptomycin in the sample will thus prevent the binding of the detector reagent to the streptomycin immobilised on the membrane, resulting in disappearance of the test line in the read out zone. Using raw milk samples, spiked with either streptomycin or dihydrostreptomycin, complete disappearance of the test line was obtained with 160 ng ml(-1) and 190 ng ml(-1), respectively. This demonstrates that the test is applicable for screening raw milk samples for the presence of (dihydro)streptomycin residues at MRL level (EU: 0.2 mg (dihydro)streptomycin kg(-1) milk). The major advantages of the one step strip test are that results can be obtained within 10 min and that all reagents are included in the test device.