Development of a biosensor immunoassay for the quantification of (alpha)S1-casein in milk

An immunoassay to quantify (alpha)S1-casein ((alpha)S1-CN) in milk using an optical biosensor, based on surface plasmon resonance (SPR) measurement, has been developed. The assay consists of a two-step sandwich strategy, with two anti-(alpha)S1-CN antibodies directed against each extremity of the molecule. This strategy permits only intact (alpha)S1-CN to be quantified and not its degradation products. The calibration curve was obtained using a reference milk powder with a known (alpha)S1-CN concentration. nalysis Atime per sample was less than ten minutes. The antibody-coated surface could be used for more than 150 determinations. Detection limit was established at 0·87 (mu)g/ml and the intra- and inter-assay variation coefficients were 2·86 and 5·31%, respectively. The method was applied to raw milk to quantify intact (alpha)S1-CN, with no pre-treatment of the sample. An initial analysis of 48 milk samples permitted (alpha)S1-CN concentrations ranging from 8·8 to 12·06 mg/ml to be obtained.