Optics and Photonics Society of Iran

Membranes are critical to the life of a cell because the structure and function of cell are dependent on membranes. Vesicle is a spherical bilayer phospholipid structure, which is known as a model for membrane of living cells. According to Fluid Mosaic Model, membranes can be considered as a two dimensional liquid in which lipids can freely diffuse on it. We are interested in studying lateral diffusion of lipids, for which there are a few reported methods to measure it. We propose a simple new method to study the lateral motion of lipid molecules based on temporal response of the lipids to an external force applied by optical tweezers. Optical tweezers are powerful tools to trap and manipulate at micro- and nano-scale using highly focused laser beam. In this research, first, a micro-spherical polystyrene bead was specifically attached to an artificial vesicle. Then a tether was formed from vesicle by applying a pulling force by optical tweezers. By applying an external force a sudden change was caused on the shape of the structure. This structure then relaxed to a final stable form. The diffusion coefficient of lipids can be experimentally investigate by studying the temporal relaxation of the deformed structure.