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In biological membranes, lipids and proteins interact with each other to regulate their functions with complex structure. Manipulation techniques of molecular dynamics are desired to elucidate the regulation mechanism mediated by the interaction of membrane molecules. Optical trapping has been applied to study the biological molecular dynamics since it allows manipulation of biomolecules labeled with single μm-sized particle at the laser focal spot in solution. Due to the complex structure of biological membrane and weak optical trapping forces, it is difficult to investigate the effects of optical trapping on molecules in the biological membrane. In this study, a simple biological membrane model, the substrate-supported lipid bilayer (SLB), was used instead of the complex biological membrane. We investigated the diffusion properties of SLB in an optical trap to clarify the optical trapping dynamics of cell surface molecules. To evaluate the diffusion of lipid molecules, a fluorescent molecule, Texas Red conjugated lipid molecule (TR-PE), was mixed in SLB. The lateral diffusion of TR-PE in an optical trap was estimated by fluorescence correlation spectroscopy (FCS). The diffusion of TR-PE in SLB was slowed down with increasing laser power, suggesting that optical forces act slightly on the molecules in the lipid bilayer. Optical trapping has the potential to assemble molecules in biological membranes due to the difference in diffusion rate of molecules between inside and outside of the focal spot.
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