AVS 53rd International Symposium
    Biomaterial Interfaces Tuesday Sessions
       Session BI-TuP

Paper BI-TuP4
Investigating Model Peptides on Surfaces using XPS, SIMS and NEXAFS

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Biomaterial Interfaces Poster Session
Presenter: J.S. Apte, University of Washington
Authors: J.S. Apte, University of Washington
L.J. Gamble, University of Washington
D.G. Castner, University of Washington
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The purpose of this investigation is to study protein-surface interactions at a fundamental level using model peptides to examine individual adsorption phenomena that comprise the collective interactions of larger proteins with surfaces. The model peptides used were made up of leucine (L) and lysine (K) amino acids arranged in specific sequences to reliably create @alpha@-helix or @beta@-sheet secondary structures. These peptides were adsorbed onto self-assembled monolayer (SAM) surfaces that have well-defined, extensively studied characteristics. The terminal functional groups of the SAMs used in these studies are a methyl group, a carboxylic acid group, an alcohol group and an amine group. Studies were also done on a plasma-deposited fluoropolymer for comparison. Initial adsorption isotherm studies with the 14-mer LK @alpha@-helix peptide showed that the adsorption behavior varied greatly on the different SAM surfaces. Percent nitrogen measured with XPS was used to determine the amount of adsorbed peptide. It was found on methyl- and COOH-terminated SAMs that adsorption from PBS formed patches of peptide with bare spots. There was no adsorption on OH-terminated SAMs and uniform adsorption on fluoropolymer. It was also found that the concentration required to achieve a partial peptide layer with some bare spots on methyl SAMs was 100-fold higher that required for COOH SAMs. Adsorption was investigated for three different buffer salt concentrations to observe the influence of ionic strength on adsorption. On methyl SAMs, it was found that no peptide adsorption was detectable from deionized water, even at peptide concentrations of 1 mg/mL. In contrast a nitrogen concentration of about 5 atomic percent was detected when adsorbed from PBS. Angle-dependent XPS and NEXAFS studies were used to probe the organization of the adsorbed peptides.