AVS 50th International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI-MoA

Paper BI-MoA3
Factors that Determine the Protein Resistance of Oligoether Self-assembled Monolayers - Internal Hydrophilicity, Terminal Hydrophilicity and Lateral Packing Density

Monday, November 3, 2003, 2:40 pm, Room 307

Session: Non-fouling Surfaces and Biolubrication
Presenter: M. Grunze, University of Heidelberg, Germany
Authors: S. Herrwerth, University of Heidelberg, Germany
W. Eck, University of Heidelberg, Germany
M. Grunze, University of Heidelberg, Germany
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Protein resistance of oligoether self-assembled monolayers (SAMs) on gold and silver surfaces has been investigated systematically in order to elucidate structural factors that determine whether a SAM will be able to resist protein adsorption. Oligo(ethylene glycol) (OEG), oligo(propylene glycol) and oligo(trimethylene glycol) terminated alkanethiols with different chain length and alkyl termination were synthesized as monolayer constituents. The packing density and chemical composition of the SAMs were examined by XPS spectroscopy; the terminal hydrophilicity was characterized by contact angle measurements. IRRAS spectroscopy gave information about the chain conformation of specific monolayers; the amount of adsorbed protein compared to alkanethiol monolayers was determined by ellipsometry. We found several factors that can suppress the protein resistance of oligoether monolayers. Monolayers with a hydrophobic interior such as those containing oligo(propylene glycol) show no protein resistance. The lateral compression of oligo(ethylene glycol) monolayers on silver generates more highly ordered monolayers and may cause decreased protein resistance, but does not necessarily lead to an all-trans chain conformation of the OEG moieties. Water contact angles higher than 70° on gold or 65° on silver reduce full protein resistance. We conclude that both internal and terminal hydrophilicity favor the protein resistance of an oligoether monolayer. It is suggested that the penetration of water molecules in the interior of the SAM is a necessary prerequisite for protein resistance. We discuss and summarize the various factors and the balance of forces which are critical for the functionality of "inert" organic films.