The determination of folic acid in milk and paediatric formulae by optical biosensor assay utilising folate binding protein

Bovine milk-derived folate binding protein was evaluated during the development of a ligand binding assay for the quantitation of folic acid. An inhibition assay format using an optical biosensor platform was automated, and was compared directly with an established assay utilising a monoclonal antibody. Alternative chemistries for immobilising folic acid to the sensor surface were considered and the optimised technique was applied to the estimation of folic acid content in milk and milk-based paediatric formulae. Samples were prepared for analysis by direct dilution into buffer and heat treatment. Analysis conditions were defined and non-specific binding considerations were evaluated. Single laboratory validation performance parameters are reported and the relative affinities for the major endogenous reduced folate in milk support the attributes of the optical biosensor assay utilising folate binding protein as compared with the antibody. The future potential for application of the described assay to total folate quantitation is discussed.