AVS 49th International Symposium
    Biomaterials Wednesday Sessions
       Session BI+AS-WeM

Paper BI+AS-WeM6
Interaction of Water with Protein Resistant Self-Assembled Monolayers: Neutron Reflectivity Measurements of Water Density in the Interphase Region

Wednesday, November 6, 2002, 10:00 am, Room C-201

Session: Ambient Surface Science Techniques
Presenter: D. Schwendel, University of Heidelberg, Germany
Authors: D. Schwendel, University of Heidelberg, Germany
T. Hayashi, University of Heidelberg, Germany
A.J. Pertsin, University of Heidelberg, Germany
R. Dahint, University of Heidelberg, Germany
R. Steitz, Hahn-Meitner-Institut, Germany
F. Schreiber, University of Oxford, UK
M. Grunze, University of Heidelberg, Germany
Correspondent: Click to Email
The interfacial behavior of surfaces, colloids, and molecules with water plays a substantial role in surface science and other areas. It is, in particular, responsible for colloid stability, micelle formation, biomembrane fusion, and the resistance of materials against proteins from biological media. These materials are of crucial importance in biotechnology and biomedical applications. One type of such bicompatible surfaces is represented by self-assembled monolayers (SAMs) on Au and Ag composed of undecanethiolates terminated oligo(ethylene glycols), (-O-CH2-CH2-)n (hereafter EGn). Neutron reflectivity measurements on protein resistant methoxy tri(ethylene glycol) (EG3-OMe) and hydroxy terminated hexa(ethylene glycol) (EG6-OH) undecanethiolate self-assembled monolayers (SAMs) in contact with deuterated water reveal the presence of an extended (~5 nm thick) water interphase with a noticeably reduced density (85-90 % of bulk water density). This result is in qualitative agreement with Grand canonical Monte Carlo simulations of water next to the SAM surface. For comparison, neutron reflectivity experiments have also been performed on non-functionalized hydrophobic octadecanethiolate and hydrophilic hydroxy terminated undecylthiolate SAMs. Additionally, neutron reflectivity measurements on protein resistant SAMs formed from hydroxy and methoxy terminated tri(ethylene glycol) (EG3-OH and EG3-OMe) against high concentrated protein solutions of BSA show that the free dissolved protein does not contact the surface but that it is repelled over a distance of few nm. The profiles strongly suggest a BSA depleted water layer at the SAM/bulk interface of 4 to 6 nm while BSA adsorption is observed for non-resistant propoxy terminated tri(ethylene glycol) (EG3-OPr).