Partial denaturation of silica-adsorbed bovine serum albumin determined by time-resolved evanescent wave-induced fluorescence spectroscopy

Time-resolved evanescent wave-induced fluorescence spectroscopy (TREWIFS) has been used in the study the molecular conformation of bovine serum albumin (BSA) adsorbed at the silica/aqueous interface. Using TREWIFS, the adsorption behavior of 1-anilinonaphthalene-8-sulfonic acid (ANS) complexed with BSA has been investigated as a function of penetration depth of the evanescent wave. Restriction of the fluorescent probe's motion as a function of distance from the interface was also studied by time-resolved evanescent wave-induced fluorescence depolarization measurements. The results are consistent with a model of a partial protein denaturation: at the surface, an adsorbed BSA molecule unfolds, thus optimizing protein-silica interactions and the number of points of attachment to the surface. Further away normal to the surface, the protein molecule maintains its coiled structure.