Control of Lipid Bilayer Phases of Cell-Sized Liposomes by Surface-Engineered Plasmonic Nanoparticles.

Liquid-ordered (Lo) phase domains, a cholesterol-rich area on lipid bilayers, have attracted significant attention recently due to their relevance to lipid rafts, the formation/collapse of which is associated with various kinds of information exchange through the plasma membrane. Here, we demonstrate that the formation/collapse of Lo phase domains in cell-sized lipo-somes, i.e., giant unilamellar vesicles (GUVs), can be controlled with bioactive plasmonic nanoparticles and light. The na-noparticles were prepared by the surface modification of gold nanorods (AuNRs) using a cationized mutant of high-density lipoprotein (HDL), which is a natural cholesterol transporter. Upon the addition of surface-engineered AuNRs to GUVs with the mixed domains of Lo and liquid-disorder (Ld) phases, the Lo domains collapsed and solid ordered (So) phase domains were formed. The reverse phase transition was achieved photothermally, with the AuNRs loaded with cholesterol. During these transitions, the AuNRs appeared to be selectively localized on the less fluidic domain (Lo or So) in the phase-mixed GUVs. These results indicate that the phase transitions occur through the membrane binding of the AuNRs followed by spontaneous/photothermal transfer of cholesterol between the AuNRs and GUVs. Our strategy to develop bioactive AuNRs potentially enables spatiotemporal control of the formation/collapse of lipid rafts in living cell.