Insights on structural variations of protein adsorption layers on hydrophobic fluorohydrocarbon polymers gained by spectroscopic ellipsometry (part I)

Adsorption layers of two human plasma proteins (albumin-HSA, fibrinogen-FGN ) on hydrophobic fluorohydro-carbon polymer (CHF) films were characterized in situ and ex situ by spectroscopic ellipsometry. The adsorbed layers were formed in phosphate buffered saline solutions of varied protein concentrat ions. Different optical five layer models were compared with respect to the evaluation of protein layers based on ellipsometric data. The Maxwell-Garn ett effective medium approximation was concluded to be advantageous in prov iding a more realistic description of the layer structure as compared to th e assumption of optical homogeneous layers. The applied models coincided wi th respect to the determination of the adsorbed amount of protein. Both the equilibrium surface concentration and the adsorption dynamics of HSA and F GN were found to depend on the solution protein concentration. The maximum adsorbed protein concentrations of the two proteins differed by ratios (HSA /FGN) of 1/4.5 in mass units and 1/0.83 in molar units (HSA: 1.0 mg m(-2) = 15 nmol m(-2); FGN: 4.5 mg m(-2) = 12.5 nmol m(-2)). No reversibility of t he adsorption of the two globulins on the polymer surface was observed upon dilution of the protein solutions with pure buffer. Coverage of the polyme r surface with respect to the adsorbed molecules was achieved by different amounts of HSA or FGN depending on the transport conditions in the adsorpti on process. The observed variations of the surface area occupied by a given protein were apparently related to re-orientations and/or intramolecular c hanges of the adsorbed molecules. Structural parameters of the protein laye rs gained by the evaluation of the ellipsometric data support this conclusi on. (C) 1999 Elsevier Science B.V. All rights reserved.