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

Abstract

Adsorption layers of two human plasma proteins (albumin-HSA, fibrinogen-FGN) on hydrophobic fluorohydrocarbon 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 concentrations. Different optical five layer models were compared with respect to the evaluation of protein layers based on ellipsometric data. The Maxwell-Garnett effective medium approximation was concluded to be advantageous in providing a more realistic description of the layer structure as compared to the assumption of optical homogeneous layers. The applied models coincided with respect to the determination of the adsorbed amount of protein. Both the equilibrium surface concentration and the adsorption dynamics of HSA and FGN 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 the adsorption of the two globulins on the polymer surface was observed upon dilution of the protein solutions with pure buffer. Coverage of the polymer surface with respect to the adsorbed molecules was achieved by different amounts of HSA or FGN depending on the transport conditions in the adsorption process. The observed variations of the surface area occupied by a given protein were apparently related to re-orientations and/or intramolecular changes of the adsorbed molecules. Structural parameters of the protein layers gained by the evaluation of the ellipsometric data support this conclusion. Copyright (C) 1999 Elsevier Science B.V.