Fluorescence Recovery after Merging a Droplet to Measure the Two-dimensional Diffusion of a Phospholipid Monolayer

Abstract

We introduce a new method to measure the lateral diffusivity of a surfactant monolayer at the fluid-fluid interface, called fluorescence recovery after merging (FRAM). FRAM adopts the same principles as the fluorescence recovery after photobleaching (FRAP) technique, especially for measuring fluorescence recovery after bleaching a specific area, but FRAM uses a drop coalescence instead of photobleaching dye molecules to induce a chemical potential gradient of dye molecules. Our technique has several advantages over FRAP: it only requires a fluorescence microscope rather than a confocal microscope equipped with high power lasers; it is essentially free from the selection of fluorescence dyes; and it has far more freedom to define the measured diffusion area. Furthermore, FRAM potentially provides a route for studying the mixing or inter-diffusion of two different surfactants, when the monolayers at a surface of droplet and at a flat air/water interface are prepared with different species, independently.

Investigation of Fusion between Nanosized Lipid Vesicles and a Lipid Monolayer Toward Formation of Giant Lipid Vesicles with Various Kinds of Biomolecules

“…The amount of rhodamine on the giant lipid vesicles showed that the fusion of the LUVs to the lipid droplet was greater than that of the LUVs to the giant lipid vesicles ( Figure 3 a–c). The difference in fusion between the LUVs and the lipid droplet and between the LUVs and the giant lipid vesicle was attributable to the lipid diffusion of the lipid droplet and the giant lipid vesicle; the lipid diffusion of the lipid droplet was higher than that of the giant lipid vesicle [ 22 , 23 ].…”