Nanoscale departures: excess lipid leaving the surface during supported lipid bilayer formation

The behavior of small liposomes on surfaces of inorganic oxides remains enigmatic. Under appropriate conditions it results in the formation of supported lipid bilayers (SLBs). During this process, some lipids leave the surface (desorb). We were able to visualize this by a combination of time-resolved fluorescence microscopy and fluorescence recovery after photobleaching studies. Our observations also allowed us to analyze the kinetics of bilayer patch growth during the late stages of SLB formation. We found that it entails a balance between desorption of excess lipids and further adsorption of liposomes from solution. These studies were performed with liposomes containing zwitterionic phospholipids (dioleoylphosphatidylcholine alone or a mixture of dioleoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and cholesterol) on TiO2 in the presence of Ca(2+) but in the absence of other salts.