Fast biosensor immunoassays for the detection of cows milk in the milk of ewes and goats

Two monoclonal antibodies (MAb) raised against bovine (kappa)-casein were developed and applied in an automated optical biosensor (Biacore 3000) to create easy and fast direct and inhibition biosensor immunoassays (BIA) for the detection of cowsʹ milk in the milk of ewes and goats. With both assay formats, low limits of detection (<0·1%) and fast run times (around 5 min) were obtained. For sample preparation, milk was diluted in buffer (direct assay) or in an antibody-containing buffer (inhibition assay) only. For quantitative analysis, calibrants of cowsʹ milk in ewesʹ or goatsʹ milk were used. Advantages of the direct BIA are: the single reagent format (biosensor chip immobilized antibodies only); the use of small amounts of antibodies (2 (mu)g for >350 tests); and the wide measurement range (0·1 to 10% cowsʹ milk). Despite these advantages, the inhibition BIA (using (kappa)-casein immobilized on the chip) was preferred because of the possible application of nonpurified Mab, the higher responses, the higher sensitivity at relevant low percentages of cowsʹ milk and its robustness (>800 cycles per chip).