Packing
Density Changes of Supported Lipid Bilayers
Observed by Fluorescence Microscopy and Quartz Crystal Microbalance-Dissipation
- Publication date
- Publisher
Abstract
Various properties of supported lipid
bilayers such as diffusion
and lipid partitioning are well characterized. However, little attention
has been paid to their molecular packing density. In this work, the
adsorption of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) vesicles
on glass and silicon dioxide was investigated using fluorescence microscopy,
quartz crystal microbalance-dissipation (QCM-D), and atomic force
microscopy. Fluorescence recovery after photobleaching data showed
that the adsorption of large unilamellar vesicles (LUVs) on glass
yielded supported bilayers with full mobility under alkaline (pH 8.3)
and acidic (pH 3–4) conditions. These fluid bilayers exhibited
quite different diffusion constants; those at alkaline pH were ∼10
times larger than those at acidic pH. The reason for this pH dependence
was clarified by investigation of the rupture of giant unilamellar
vesicles (GUVs) on glass. Fluorescence data revealed that the area
of planar bilayer patches increased at alkaline pH. Thus, we conclude
that the rapid diffusion in alkaline solution arises from the decreased
molecular density. QCM-D data showed that dissipation increased in
a stepwise manner during vesicle fusion on silicon dioxide at alkaline
pH. We attribute this behavior to the decrease in packing density
of planar bilayers