Ellipsometry studies of fibronectin adsorption

Abstract

The adsorption of fibronectin on a series of different surfaces was investigated with in situ ellipsometry. For silica and methylated silica, the adsorbed amount (Γ), the adsorbed layer thickness ( δ el) and the mean adsorbed layer refractive index ( n f) were obtained by a procedure involving studies of the bare substrate at two different ambient refractive indices, as well as four-zone averaging. It was found that the adsorbed amount of fibronectin was the same (1.9 ± 0.1 mg m −2) on both silica and methylated silica surfaces. However, the adsorbed layers formed on methylated silica were more extended and had a lower average protein concentration than those formed on silica. Furthermore, on both silica and methylated silica, an increasing adsorbed amount is achieved both by a denser packing of the fibronectin molecules and by a growth of the adsorbed layer normal to the surface. Furthermore, the adsorption of fibronectin on lipid surfaces was investigated. It was found that the adsorption of fibronectin on phosphatidic acid was quite significant (2.2 ± 0.2 mg m −2), while that on phosphatidylcholine, phosphatidylinositol and phosphatidylserine was much smaller (all 0.1 ± 0.05 mg m −2). These results are correlated to findings on the adsorption of fibrinogen on these surfaces, as well as on the opsonization of lipid-stabilized colloidal particles.