Determination of lactoferrin in bovine milk, colostrum and infant formulas by optical biosensor analysis

An automated, rapid, sensitive and label-free biosensor-based immunoassay for lactoferrin in bovine milk utilising surface plasmon resonance (SPR) optical detection is described. Lactoferrin content is estimated from its specific interaction with an anti-bovine lactoferrin antibody immobilised on the sensor surface in a direct- binding assay format. Samples are prepared for analysis by direct dilution into buffer. Analysis conditions, including ligand immobilisation, flow-rate, contact time and regeneration have been defined and non-specific binding considerations evaluated. Performance parameters include a working range of 0-1000 ng mL−1, a method-detection limit of 19.9 μg mL−1 in undiluted milk, overall instrument response RSDR of 3.50%, a mean inter-assay RSDR of 10.8% for milk and surface stability over ca 500 samples. The technique was applied to the measurement of lactoferrin content of consumer milks, colostrum and infant formulas, and temporal change during early bovine lactation.