Aggregation of HSA, IgG, and Fibrinogen on Methylated Silicon Surfaces

Ellipsometry was used to quantify adsorption and tapping mode atomic force microscopy to study surface aggregation of human serum albumin (HSA), immunoglobulin G (IgG), and fibrinogen (Fib) adsorbed from aqueous solutions onto methylated silicon surfaces. After exposure to air the protein monolayers were spontaneously restructured, exposing disorganized areas with heterogeneity depending on the degree of surface methylation. The aggregation patterns also depended on some properties of the adsorbed protein (such as the number of contact points with the surface), but seemed to be almost independent of the adsorption time. The results indicate that aggregates were formed due to lateral reorganization on the adsorbed layer at the air-liquid interface during the drying process. The interpretation is that the heterogeneous structures result from a thermodynamically driven interaction between the hydrophobic surface and the similarly hydrophobic air. The main conclusion that can be extracted from this work is that fibrinogen (hydrophobic and large protein) interacts more irreversibly with the silicon surfaces than IgG, and much more so than HSA, which is less hydrophobic and smaller than fibrinogen. Copyright 1998 Academic Press.

In vitro plasma protein adsorption and kallikrein formation on 3-mercaptopropionic acid, L-cysteine and glutathione immobilized onto gold

3-Mercaptopropionic acid (MPA), L-cysteine (L-cys), and glutathione (GSH) monolayers were immobilized onto gold and used in in vitro protein tests. The surfaces were characterized with ellipsometry, static contact angle measurements, atomic force microscopy, and Fourier transform infrared reflection absorption spectroscopy (FT-IRAS). After incubations in human plasma and antibody solutions, the surface antisera binding patterns were determined with ellipsometry. Using serum instead of plasma, complement activation was studied in the same fashion. Activated coagulation Factor XII and kallikrein formation on the surfaces and in the plasma were studied using a kallikrein-specific colorimetric assay. 3-Mercaptopropionic acid indicated contact activation of coagulation but L-cysteine did not. Glutathione displayed low deposition of plasma proteins, large deposition of proteins from serum, and did not promote kallikrein formation. None of the surfaces could be attributed complement activating properties, as determined by antibody deposition. The present study demonstrates that surface biology in complex model systems can be conveniently studied in vitro through systematic and well defined surface modifications.