Evolution of supported planar lipid bilayers on step-controlled sapphire surfaces.

Self-organized step/terrace structures on a sapphire surface were used to investigate interface properties between a solid surface and a supported planar lipid bilayer (SPB). We prepared random-stepped, single-stepped and multistepped sapphire surfaces. Some multistepped surfaces covered with crossing steps exhibit phase-separation into hydrophilic and hydrophobic domains. We studied evolution of self-spreading lipid bilayers that are subject to the atomic structures and chemical states on the surfaces. The growth direction of SPBs in the self-spreading method is regulated by the atomic steps. While the SPBs were apparently uniform after a 1 h self-spreading, a density gradient of the lipid molecules was observed even after 24 h spreading. We found that various patterns of the SPBs that depend on the density of the lipid molecules are self-assembled on the phase-separated surfaces. Although the SPB is supported on the sapphire surface via an about 1 nm water layer, the self-spreading direction and the morphology of the SPBs are affected by the atomic steps, whose height is much smaller than that of the water layer.