Quartz crystal microbalance immunosensor for the quantification of immunoglobulin G in bovine milk

The development of precise and sensitive methods for milk analysis remains a challenging task in the milk quality control field. A piezoelectric immunosensor was developed for the real-time quantification of immunoglobulin G (IgG) in bovine milk and colostrum. The sensing surface was designed with rabbit antibovine IgG as the detecting molecule, coupled onto a carboxymethyl dextran-coated gold crystal. Total binding and non-specific binding were measured using a quartz crystal microbalance with dissipation (QCM-D). Conditions of analysis, including ligand immobilization, dilution ratio of milk, salinity, and pH of the dilution buffer were optimized by Doehlert experimental design in order to enhance the detection specificity. The performances of the optimized immunosensor were evaluated. The standard curve was established from QCM-D responses and was linear until an IgG concentration of 2500 ng/mL, with a detection limit of 46 ng/mL. The total assay time is 5 min per sample, including the regeneration step. The intra- and inter-assay variation coefficients were equal to or below 4.7 and 6.1%, respectively. The sensing surface was stable for 100 analyses. This technique was successfully applied to the detection of colostrum addition in milk, with a minimum threshold of 0.1%. This new IgG quantification method is particularly interesting as a cost-effective and time-saving alternative for the dairy analytical laboratories when compared with the existing quantification methods.