Figure 1.

A fluorescent-based single particle assay to measure selective sophorolipid (SL) micelles interactions with liposomes tethered on passivated surfaces. (A) Cartoon representation of the single liposome assay to directly observe distinct and successive SL micelle docking event on liposomes. Biotinylated liposomes of different diameters are labeled with ATTO-655 and immobilized on a streptavidin-functionalized surface. The SL micelles labeled with a second chromophore (DiO-488) are added to the solution and allowed to interact with surface-tethered liposomes. Parallel imaging of the two different channels is acquired with a Total Internal Reflection Fluorescence (TIRF) microscope. The background corrected fluorescence intensity obtained from the red channel is used to quantify liposome spatial localization and observe directly the interaction of SL micelles in the blue channel. (B) Typical trajectories of SL micelle interaction on liposomes. Red color represents the successful docking of SL micelles on a liposome followed by chromophore photobleaching. The blue color represents kiss-and-run events where micelles transiently interacts with a liposome. A fraction of liposomes on the surface does not show any docking events; therefore, the trace displays the constant intensity over time. Similar profile traces (represents by Black color) were observed for non-fluorescently labeled SLs, liposomes labeled with DiO or DiO alone.