Domain Localization by Graphene Oxide in Supported Lipid Bilayers

The gel-phase domains in a binary supported lipid bilayer (SLB) comprising dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) were localized on graphene oxide (GO) deposited on a SiO(2)/Si substrate. We investigated the distribution of the gel-phase domains and the liquid crystalline (L(α)) phase regions in DOPC+DPPC-SLB on thermally oxidized SiO(2)/Si substrates with GO flakes to understand the mechanism of the domain localization on GO. Fluorescence microscopy and atomic force microscopy revealed that the gel-phase domains preferably distributed on GO flakes, whereas the fraction of the L(α)-phase increased on the bare SiO(2) surface which was not covered with the GO flakes. The gel-phase domain was condensed on GO more effectively at the lower cooling rate. We propose that nucleation of the gel-phase domain preferentially occurred on GO, whose surface has amphiphilic property, during the gel-phase domain formation. The domains of the liquid ordered (L(o)) phase were also condensed on GO in a ternary bilayer containing cholesterol that was phase-separated to the L(o) phase and the liquid disordered phase. Rigid domains segregates on GO during their formation process, leaving fluid components to the surrounding region of GO.