Microscope observation of united liposome trajectories near a polarized ultramicroelectrode surface

Abstract

An optical setup, based on ultramicroscopy principles, was built to track and measure the velocities of phospholipid liposomes in the vicinity of a polarized ultramicroelectrode. This custom device allowed to link the presence or the absence of blocking impacts at the electrode surface to the experimental conditions (redox probe and applied potential). Varying the potential of a disk ultramicroelectrode changes the motion of liposomes in a solution containing redox species (ferrocyanide or ferricyanide). Our ultramicroscopy setup demonstrated the existence of electroosmosis, which repels the liposomes or attracts them to the ultramicroelectrode surface. This observation highlights the mobility behavior of liposomes in solution near a polarized ultramicroelectrode, in blocking impact experiments with different conditions (redox probes and applied potentials). In contrast to the usual microscopy view showing the electrode surface, the side view of our ultramicroelectrode in solution is an original approach that allowed to openly observe the plane containing the trajectories of liposomes between the bulk solution and the electrode surface, and to use particle image velocimetry (PIV) to measure the solvent velocity in this region.