AVS 53rd International Symposium
    Biomaterial Interfaces Friday Sessions
       Session BI-FrM

Paper BI-FrM6
Temperature Stability of Protein Monolayers Studied by Ellipsometry in the Infrared, Visible and Ultraviolet Spectral Regions

Friday, November 17, 2006, 9:40 am, Room 2014

Session: Biomolecular Surface Characterization II
Presenter: H. Arwin, Linköping University, Sweden
Authors: H. Arwin, Linköping University, Sweden
D.W. Thompson, University of Nebraska, Lincoln
J.A. Woollam, University of Nebraska, Lincoln
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Future devices based on bionanotechnology may contain protein layers and temperature stability will be an issue. One way to monitor temperature induced structural changes in protein molecules adsorbed in monolayers on solid substrates is to analyze the complex-valued refractive index N=n+ik as determined by spectroscopic ellipsometry. In the infrared spectral (IR) region ellipsometry provides a quantification of the amide band parameters of the adsorbed protein molecules and in the visible (VIS) and ultraviolet (UV) regions the layer thickness (surface mass density) can be determined as well as the electronic contributions to N. Earlier studies on protein multilayers (human serum albumin and its antibody) show that heating above 100 °C causes structural changes observed as changes of the amide bands. Heating to 200 °C causes layer degradation seen as irreversible changes in n and k and also a substantial decrease in surface mass density. The objective is here to present methodology and results from pilot studies of effects of heating monolayers of proteins adsorbed on gold substrates. The surface mass density and N=n+ik are determined with spectroscopic ellipsometry (UV-VIS-IR) equipped with a heat stage (20 - 300 °C). A model refractive index function is applied to the optical properties of the protein layer and changes in the model parameters are monitored at elevated temperatures with special emphasis on the amide I band around 1640 cm@super -1@, the amide II band around 1520 cm@super -1@ and the amide A band in the 2800 - 3300 cm@super -1@ region.