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

Abstract

The formation of a supported planar lipid bilayer (SPLB) and its morphology on step-and-terrace rutile TiO 2(100) surfaces were investigated by fluorescence microscopy and atomic force microscopy. The TiO 2(100) surfaces consisting of atomic steps and flat terraces were formed on a rutile TiO 2 single-crystal wafer by a wet treatment and annealing under a flow of oxygen. An intact vesicular layer formed on the TiO 2(100) surface when the surface was incubated in a sonicated vesicle suspension under the condition that a full-coverage SPLB forms on SiO 2, as reported in previous studies. However, a full-coverage, continuous, fluid SPLB was obtained on the step-and-terrace TiO 2(100) depending on the lipid concentration, incubation time, and vesicle size. The SPLB on the TiO 2(100) also has step-and-terrace morphology following the substrate structure precisely even though the SPLB is in the fluid phase and an approximately 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 TiO 2(100) gains 20 times more energy than on SiO 2. This specifically strong attraction on TiO 2 makes the fluid SPLB precisely follow the substrate structure of angstrom order.

Interfacing Zwitterionic Liposomes with Inorganic Nanomaterials: Surface Forces, Membrane Integrity, and Applications

“…23,24 On the other hand, with a high liposome concentration and a long incubation time, Tero et al claimed that PC liposomes can form similar bilayers on TiO2 (100) as that on SiO2 based on van der Waals interaction, and the attraction potential is 20-fold larger on TiO2. 25 Others reported that low pH, or incorporation of anionic lipids plus Ca 2+ is needed to form SLBs on TiO2. [26][27][28] The above studies mainly employed bulk planar TiO2 surfaces, and the overall impression is that it is more difficult to form PC SLBs on TiO2.…”

A Stable Lipid/TiO2 Interface with Headgroup-Inversed Phosphocholine and a Comparison with SiO2

“…25 A number of previous studies investigated the interaction between liposomes and TiO2 surfaces, where both liposome fusion and simple adsorption were reported depending on the lipid composition. [26][27][28][29][30][31][32][33][34][35] It needs to be noted that fusion takes place with negatively charged phosphatidylserine (PS) lipids in the presence of Ca 2+ , while liposomes composed solely of zwitterionic phospholipids only undergo adsorption in physiological conditions. Some work reported planar zwitterionic bilayers on TiO2 under acidic conditions.…”

Formation and fluidity measurement of supported lipid bilayer on polyvinyl chloride membrane

“…In case of an adhesive vesicular layer, the photobleached region remains and no recovery proceeds because the vesicles were immobile and isolated from each other. 18,26,27 The bright spots in Figs. 4 and 5 were adsorbed vesicles, but we could not judge whether they adsorb on the SLB or on the substrate from the fluorescence images.…”

“…A thermally oxidized SiO 2 /Si substrate was also used as a control, because it is a standard sample in our previous studies, [18][19][20][21] where the preparation of vesicle suspensions and SLBs are described in more detail.…”

“…Figure 5 shows the typical example of the FRAP performed in the same condition as Fig.4 for the fluid and continuous DOPC-SLB on a thermally oxidized SiO 2 /Si substrate. 18,19 The lipid molecules diffuse in a lipid bilayer, thus the fluorescence intensity of the photobleached region temporally in a continuous SLB. In case of an adhesive vesicular layer, the photobleached region remains and no recovery proceeds because the vesicles were immobile and isolated from each other.…”