Lateral diffusion of bovine serum albumin adsorbed at the solid-liquid interface

The lateral mobility of eosin isothiocyanate-labeled bovine serum albumin irreversibly adsorbed to poly(methylmethacrylate) (PMMA) and poly(dimethylsiloxane) (PDMS) surfaces from aqueous solution was measured by a combination of total internal reflection fluorescence and fluorescence recovery after pattern photobleaching techniques. Lateral mobility over distances of several micrometers was probed by photobleaching and monitoring fluorescence with the fringe pattern formed by two intersecting coherent laser beams in total internal reflection. The period of the fringes determined the characteristic length for transport on the surface and was varied by changing the angle of intersection. The dependence of the fluorescence recovery time on the period of the fringes indicates that lateral migration of the adsorbed protein on PMMA is by surface diffusion with D = (1.2 ± 0.3) × 10−9cm2/s, while the extent of fluorescence recovery reveals the coexistence of a mobile population and a population that is apparently immobile over 20 min. For comparison, D = (2.6 ± 0.1) × 10−9cm2/s on PDMS.