AVS 47th International Symposium
    Biomaterial Interfaces Monday Sessions
       Session BI+SS-MoM

Paper BI+SS-MoM6
The Interaction of Phospholipid Vesicles with Binary Alkanethiol/Hydroxythiol Monolayers

Monday, October 2, 2000, 10:00 am, Room 202

Session: Biological Surface Science
Presenter: V. Silin, National Institute of Standards and Technology
Authors: V. Silin, National Institute of Standards and Technology
H. Wieder, Max Planck Institute for Polymer Research, Germany
J. Woodward, National Institute of Standards and Technology
A. Plant, National Institute of Standards and Technology
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Surfaces modified by self-assembly have applications in sensors, diagnostics, chemical processing, and biomaterials, where they may incorporate features such as molecular recognition and enzymatic activity. Understanding the forces that direct self-assembly of biologically important molecules in predictable arrangements will aid the development of such applications. The focus of this study is a mimic of biological membranes formed by the interaction between two self-assembled systems: phospholipid amphiphiles that associate into bilayer vesicles in water, and monolayers of alkanethiols on metal surfaces. We have studied the interaction of small (60nm) POPC vesicles with binary thiol monolayers of known surface free energy. The surfaces were prepared on gold by self-assembly from binary solutions of the thiols CH3-(CH2)10-X (X = CH3; OH) in THF. The surface plasmon resonance (SPR) technique was utilized to follow the vesicle fusion kinetics and to characterize the resulting assemblies. A dramatic influence of the surface layer composition on the formation of POPC films was observed. The formation of an additonal POPC monolayer was detected only on the completely hydrophobic (100% CH3) surface. The largest thickness of POPC layer was detected at a CH3/ OH ratio of 50% (in the assembly solution). For the completely hydrophilic surface (100 % OH) the POPC layer thickness was found to be close to the thickness of a phospholipid bilayer. Thus, the increase of hydrophilic component on the surface leads to the formation of an unordered POPC film that seems to contain a mix of fused and unfused vesicles. Most likely the formation of an ordered bilayer of POPC molecules has been observed for the completely hydrophilic surface. The SPR data were supported by AFM, capacitance and contact angle measurements.