Moving-wall-driven flows in nanofluidic systems

We describe fluidic control in lipid nanotubes 50-150 nm in radius, conjugated with surface-immobilized unilamellar lipid bilayer vesicles (∼5-25 μm in diameter). Transport in nanotubes was induced by continuously increasing the surface tension of one of the conjugated vesicles, for example, by ellipsoidal shape deformation using a pair of carbon microfibers controlled by micromanipulators as tweezers. The shape deformation resulted in a flow of membrane lipids toward the vesicle with the higher membrane tension; this lipid flow in turn moved the liquid column inside the nanotube through viscous coupling. Thus, micrometer-sized vesicles are used as a handle for controlling fluid flow inside nanometer-sized channels. We show transport and trapping of a single 30-mn-diameter carboxylate-modified latex particle inside a ∼100-nm-radius nanotube. Fluidic control in nanometer-sized channels using a moving wall provides pluglike liquid flows, offers a means for efficient routing and trapping of small molecules, polymers, and colloids, and offers new opportunities to study chemistry in confined spaces. Networks of nanotubes and vesicles might serve as a platform to build nanofluidic devices operating with single molecules and nanoparticles.