Local concentration of gel phase domains in supported lipid bilayers under light irradiation in binary mixture of phospholipids doped with dyes for photoinduced activation.

Recently, lipid bilayers supported on solid substrates are considered to offer potential as biological devices utilizing biological membranes and membrane proteins. In particular, artificially patterned supported bilayers hold great promise for the development of biological devices. In this study, we show control of the formation and location of phase-separated domain structures by light irradiation for gel phase and liquid-crystalline phase separation structures in a DMPC-DOPC binary lipid bilayer tagged with dye molecules on SiO2/Si substrates. Upon light irradiation, the gel phase domain structures disappeared from the phase-separated bilayers. This disappearance indicates that the light irradiation causes a local increase in the temperature of the lipid bilayer. In this disappearance phenomenon, the photoinduced activation of dye lipids, e.g. fluorescent lipids, is considered to play an important role, since the same phenomenon does not occur in lipid bilayers that have a low concentration of dye lipids. Thus, the local increase in temperature is propagated by light absorption of the dye lipid and subsequent photoinduced activation of nonradiative molecular vibrations. Subsequent interruption of the photoinduced activation for molecular motion allowed the gel phase domain structures to precipitate and grow again. Moreover, the domain area fraction remaining after the photoinduced activation was higher than that before the photoinduced activation. This result indicates that the local increase in temperature propagated by dye-excitation enhances formation of the gel phase domains. By utilizing this phenomenon, we could preferentially induce formation of domain structures within the light-irradiated regions. This technique could be the basis for a new patterning technique based on domain structures. Moreover, these domain structure patterns can be eliminated by increasing the temperature, allowing rewritable patterning.