We demonstrate that a transition from a compact geometry (sphere) to a structured geometry (several spheres connected by nanoconduits) in nanotube-vesicle networks (NVNs) induces an ordinary enzyme-catalyzed reaction to display wavelike properties. The reaction dynamics can be controlled directly by the geometry of the network, and such networks can be used to generate wavelike patterns in product formation. The results have bearing for understanding catalytic reactions in biological systems as well as for designing emerging wet chemical nanotechnological devices.

We demonstrate a complete nanotube electrophoresis system (nanotube radii in the range of 50 to 150 nm) based on lipid membranes, comprising DNA injection, single-molecule transport, and single-molecule detection. Using gel-capped electrodes, electrophoretic single-file transport of fluorescently labeled dsDNA molecules is observed inside nanotubes. The strong confinement to a channel of molecular dimensions ensures a detection efficiency close to unity and identification of DNA size from its linear relation to the integrated peak intensity. In addition to constituting a nanotechnological device for identification and quantification of single macromolecules or biopolymers, this system provides a method to study their conformational dynamics, reaction kinetics, and transport in cell-like environments.electrophoresis ͉ lipid ͉ conformation C ontrolled transport, interrogation, and manipulation of single molecules in integrated nanoscale devices would provide new tools for fundamental studies of molecular properties, development of ultrasensitive biochemical assays, and new models for studies of transport and reaction phenomena in confined biological systems. For example, it was recently shown that lipid bilayer nanotubes Ϸ50-200 nm in diameter are involved in mediated transport of water-soluble and membrane-bound components between cells (1). Such observations do not only raise important questions about transport mechanisms for macromolecules and organelles in spaces comparable to the size of the cargo itself, but also about how such strong confinement affects diffusion, conformation, and chemical reactions of enclosed molecules and particles (2-4). Furthermore, along with previous understanding of sorting and routing of individual molecules, e.g., in the Golgi-endoplasmic reticulum network (5, 6), these observations point out clearly that what has been an engineering dream for decades, i.e., to create manmade devices that can operate with single molecules in a controlled fashion, is a reality in biology and therefore can be a reality in the world of engineering provided that we procure sufficient knowledge and tools to emulate these systems. However, experimental systems for controlled confinement and transport of materials dissolved in fluids approaching the theoretical size limit, i.e., where the ratio of channel inner diameter and dimensions of the cargo are close to unity, have been difficult to make in combination with transport control. This difficulty is mainly because these systems have been fabricated by using solid-state materials and processing technologies used in the computer industry that are limited in terms of the smallest accessible length scales, topologies, materials properties, complexity of fabrication, and their necessary integration to large-scale instrumentation to drive fluid flow. Nonetheless, powerful micro͞nanofluidic protocols for polymer transport in solid-state nanochannels and pores (7-12) as well as in polydimethylsiloxane channels of a few micrometers in diameter (13, 14) have be...

We explore possibilities to construct nanoscale analytical devices based on lipid membrane technology. As a step toward this goal, we present nanotube-vesicle networks with fluidic control, where the nanotube segments reside at, or very close (<2 microm) to optically transparent surfaces. These nanofluidic systems allow controlled transport as well as LIF detection of single nanoparticles. In the weak-adhesion regime, immobilized vesicles can be approximated as perfect spheres with nanotubes attached at half the height of the vesicle in the axial (z) dimension. In the strong-adhesion regime (relative contact area, Sr* approximately 0.3), nanotubes can be adsorbed to the surface with a distance to the interior of the nanotubes defined by the membrane thickness of approximately 5 nm. Strong surface adsorption restricts nanotube self-organization, enabling networks of nanotubes with arbitrary geometries. We demonstrate LIF detection of single nanoparticles (30-nm-diameter fluorescent beads) inside single nanotubes. Transport of nanoparticles was induced by a surface tension differential applied across nanotubes using a hydrodynamic injection protocol. Controlled transport in nanotubes together with LIF detection enables construction of nanoscale fluidic devices with potential to operate with single molecules. This opens up possibilities to construct analytical platforms with characteristic length scales and volume orders of magnitudes smaller than employed in traditional microfluidic devices.

Nanofluidic devices are rapidly emerging as tools uniquely suited to transport and interrogate single molecules. We present a simple method to rapidly obtain compact surfactant nanotube networks of controlled geometry and length. The nanotubes, 100-300 nm in diameter, are pulled from lipid vesicles using a micropipet technique, with multilamellar vesicles serving as reservoirs of surfactant material. In a second step, the nanotubes are wired around microfabricated SU-8 pillars. In contrast to unrestrained surfactant networks that minimize their surface free energy by minimizing nanotube path length, the technique presented here can produce nanotube networks of arbitrary geometries. For example, nanotubes can be mounted directly on support pillars, and long stretches of nanotubes can be arranged in zigzag patterns with turn angles of 180 degrees. The system is demonstrated to support electrophoretic transport of colloidal particles contained in the nanotubes down to the limit of single particles. We show that electrophoretic migration velocity is linearly dependent on the applied field strength and that a local narrowing of the nanotube diameter results from adhesion and bending around SU-8 pillars. The method presented here can aid in the fabrication of fully integrated and multiplexed nanofluidic devices that can operate with single molecules.