Extension and measurements on multicomponent phospholipid vesicles by use of dual-beam optical tweezers

A micrometer-sized giant vesicle is studied by extending from the inside by using dual-beam optical tweezers in order to measure mechanical properties such as bending rigidity and surface tension of the membrane. As a micrometer-sized vesicle is extended, its shape gradually changes from a sphere to a lemon-shape, and discretely the lemon-shape deforms into a shape of a tube beside a sphere or a lemon part. The surface tension and the bending rigidity of the lipid membrane are obtained from the measured force-extension curve. In the one-phase vesicle, it is found that the surface tension is increasing as the charged component increasing, but the bending rigidity remains almost constant. In the phase-separated vesicle, the characteristic deformation different from one in the one-phase vesicle has been observed.