Lipid Bilayer Membrane with Atomic Step Structure: Supported Bilayer on a Step-and-Terrace TiO2(100) Surface

The formation of a supported planar lipid bilayer (SPLB) and its morphology on step-and-terrace rutile TiO2(100) surfaces were investigated by fluorescence microscopy and atomic force microscopy. The TiO2(100) surfaces consisting of atomic steps and flat terraces were formed on a rutile TiO2 single-crystal wafer by a wet treatment and annealing under a flow of oxygen. An intact vesicular layer formed on the TiO2(100) surface when the surface was incubated in a sonicated vesicle suspension under the condition that a full-coverage SPLB forms on SiO2, as reported in previous studies. However, a full-coverage, continuous, fluid SPLB was obtained on the step-and-terrace TiO2(100) depending on the lipid concentration, incubation time, and vesicle size. The SPLB on the TiO2(100) also has step-and-terrace morphology following the substrate structure precisely even though the SPLB is in the fluid phase and an similar to 1-nm-thick water layer exists between the SPLB and the substrate. This membrane distortion on the atomic scale affects the phase-separation structure of a binary bilayer of micrometer order. The interaction energy calculated including DLVO and non-DLVO factors shows that a lipid membrane on the TiO2(100) gains 20 times more energy than on SiO2. This specifically strong attraction on TiO2 makes the fluid SPLB precisely follow the substrate structure of angstrom order.