AVS 51st International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoM

Paper BI-MoM3
Protein-Surface Interactions Studied with Internal Reflection Ellipsometry

Monday, November 15, 2004, 9:00 am, Room 210D

Session: In-Situ Spectroscopy of Biomolecules at Interface
Presenter: H. Arwin, Linköping University, Sweden
Authors: H. Arwin, Linköping University, Sweden
M. Poksinski, Linköping University, Sweden
Correspondent: Click to Email
Spectroscopic ellipsometry (SE) used in internal reflection mode exhibits very large sensitivity for in situ protein adsorption on thin metal layers if used at surface plasmon (SP) resonance conditions@footnote 1@. Compared to external SE, the protein layer induced changes in the ellipsometric parameter @DELTA@ are several orders of magnitude larger. Using this high sensitivity it becomes possible to extract more details than only protein surface mass density (or film thickness) from SE data. In situ determination of the microstructure of adsorbed protein layers, e. g. in terms of mass distribution perpendicular to a surface, is within reach. Another implication is an increased sensitivity in biosensor applications. The enhanced sensitivity is here verified experimentally with adsorption studies of human serum albumin on gold and the possibility to model protein layer microstructure from SE data is demonstrated. Access to such detailed information is of relevance to understand conformation, surface interaction, dynamics and function of proteins at interfaces. The increased sensitivity is discussed in a thin film approximation of the complex reflectance ratio. It is found that the @DELTA@-sensitivity is inversely proportional to the difference between the damping @GAMMA@ of an SP if the metal is semi-infinite and the change in damping due to that the metal film is thin. The SE sensitivity is thus in principle unlimited as the metal-film induced change in damping can be selected with the film thickness and made to match @GAMMA@. However, the sensitivity becomes finite due to non-idealities of the sample, beam divergence, finite bandwidth of the light, etc. @FootnoteText@ 1. H Arwin, M Poksinski and K Johansen, Total internal reflection ellipsometry: principles and applications, Appl Opt, in press; M Poksinski and H Arwin, Protein monolayers monitored by internal reflection ellipsometry, Thin Solid Films 455-456 (2004) 716-721.