Electrophoretic Transport of Latex Particles in Lipid Nanotubes

Abstract

Lipid vesicles can be connected by membrane nanotubes to build networks with promising bioanalytical properties. Here we characterize electrophoretic transport in such membrane tubes, with a particular eye to how their soft-material nature influences the intratube migration. In the absence of field, the tube radius is 110 +/- 26 nm, and it remains in this range during electrophoresis even though the applied electric field causes a slight decrease in the tube radius (approximately 6-11%). The electrophoretic velocity of the membrane wall (labeled with quantum dots) varies linearly with the field strength. Intratube migration is studied with latex spheres of radii 15, 50, 100, and 250 nm. The largest particle size does not enter the tube at fields strengths lower than 1250 V/m because the energy cost for expanding the tube around the particles is too high. The smaller particles migrate with essentially the same velocity as the membrane at low fields. Above 250 V/cm, the 15 nm particles exhibit an upward deviation from linear behavior and in fact migrate faster than in free solution whereas the 100 nm particles deviate downward. We propose that these nonlinear effects arise because of lipid adsorption to the particles (dominating for 15 nm particles) and a pistonlike compression of the solvent in front of the particles (dominating for 100 nm). As expected from such complexities, existing theories for a sphere migrating in a rigid-wall cylinder cannot explain our velocity results in lipid nanotubes.

Intercellular nanotubes: insights from imaging studies and beyond

“…For instance, such measurements with soybean lipid composition have yielded nanotube radii of 110 ± 26 nm. 73 As the tubes coalesce during micromanipulation, they rearrange into three-way junctions (Y-junction) and a similar mechanism can induce self-organization and restructuring of the NVN. 74,75 Similarly, three-way junctions 51 and V–Y transitions 10,50 have been observed in ICNs (Figure 7.2).…”

Generation of phospholipid vesicle-nanotube networks and transport of molecules therein

“…Different regimes of exchange of matter have been investigated by us. In particular, the transport of small molecules and nanoparticles by diffusion [31][32][33] , by membrane tension-driven (Marangoni) flow 34 and through electrophoretic migration 35,36 were studied in detail (Fig. 1, stage VI).…”

Radial Sizing of Lipid Nanotubes Using Membrane Displacement Analysis

“…17−19 As lipid nanotubes are significantly below the resolution limit of optical microscopy, 20 accurate sizing determination has, thus far, proven extremely challenging.…”

“…Deterministic approaches, such as tether coalescence 17,18 and electrochemical detection of diffusional species, 19 use a critical physical parameter to determine the size, by measuring the contact angle of coalescence and flow of ions within the nanotube, respectively. Direct measurement by imaging remains a possibility but requires a fast super resolution technique, such as STED, to approach labile species at such short length scales.…”

“…Coalescence measurements yield external nanotube radii, 17,18 requiring accurate determination of the tube angle and position. Diffusional conductivity measurements estimate the internal radii to be 21–67 nm, 19 requiring electroactive species, which may be attenuated by strong analyte/membrane interactions.…”