Molecular and supramolecular structure of adsorbed fibrinogen and adsorption isotherms of fibrinogen at quartz surfaces.

The adsorption of fibrinogen to quartz surfaces was measured by ellipsometry, ELISA, and electron microscopy. The initial adsorption at low concentrations was diffusion rate limited as determined by the ELISA and by counting the number of adsorbed molecules at electron micrographs. From ellipsometry, ELISA, and electron microscopy measurements it was found that the surface concentration of adsorbed fibrinogen increased continuously over four decades in bulk concentration of fibrinogen. At a hydrophilic quartz surface a plateau level of the adsorption isotherm was found at a surface concentration of 0.1 pmol/cm2 where the adsorbed molecules had a mean intermolecular distance of 10 +/- 5 nm between neighbors. At higher surface concentrations the molecules were densely packed and formed a layer where single molecules could not be identified. Adsorbed fibrinogen showed different structure at hydrophobic and hydrophilic quartz surfaces. At a hydrophilic surface, the fibrinogen molecules appeared as a 46 nm nodose rod consisting of 6-7 nodes with a diameter of 4 nm. At a hydrophobic surface, the molecule appeared as a binodular or trinodular rod with a node diameter of 5-9 nm, connected with a thin filament to form a 40-nm rod. Adsorption from higher concentrations of fibrinogen in solution resulted in adsorbed spheric structures with a diameter of 18-24 nm at the hydrophobic surface and in end-to-end polymers at the hydrophilic quartz membrane.