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We present the electrochemical response to single adrenal chromaffin vesicles filled with catecholamine hormones as they are adsorbed and rupture on a 33 μm diameter disk-shaped carbon electrode. The vesicles adsorb onto the electrode surface and sequentially spread out over the electrode surface, trapping their contents against the electrode. These contents are then oxidized, and a current (or amperometric) peak results from each vesicle that bursts. A large number of current transients associated with rupture of single vesicles (86%) are observed under the experimental conditions used, allowing us to quantify the vesicular catecholamine content.

We describe a novel micropipet-assisted technique for the construction of complex, surface-immobilized two-dimensional microscopic networks of unilamellar phospholipid bilayer vesicles (1−50 μm in diameter, 10-15−10-12 L) interconnected by lipid nanotubes (100−300 nm in diameter). As starting material for the construction of networks, we used twinned vesicle pairs, one of which is multilamellar and functions as a membrane donor and the other unilamellar and functions as a membrane acceptor upon manipulation. By electromechanical insertion of a pipet tip into the unilamellar vesicle followed by lateral pulling of the micropipet away from the vesicle, a nanotube was formed. Buffer solution contained in the pipet was then injected into the nanotube orifice, forming a vesicle of controlled size that was immobilized on the surface. The networks have controlled connectivity and are well-defined with regard to the container size, angle between nanotube extensions, and nanotube length. The internal fluid composition of individual vesicles is defined during the formation of a network by selection of the solution contained in the micropipet.

We present a microelectrofusion method for construction of fluidstate lipid bilayer networks of high geometrical complexity up to fully connected networks with genus ‫؍‬ 3 topology. Within networks, self-organizing branching nanotube architectures could be produced where intersections spontaneously arrange themselves into three-way junctions with an angle of 120°between each nanotube. Formation of branching nanotube networks appears to follow a minimum-bending energy algorithm that solves for pathway minimization. It is also demonstrated that materials can be injected into specific containers within a network by nanotubemediated transport of satellite vesicles having defined contents. Using a combination of microelectrofusion, spontaneous nanotube pattern formation, and satellite-vesicle injection, complex networks of containers and nanotubes can be produced for a range of applications in, for example, nanofluidics and artificial cell design. In addition, this electrofusion method allows integration of biological cells into lipid nanotube-vesicle networks.T he last two decades have witnessed a tremendous development in miniaturization of fluidic devices. The rapid progress in processing hard materials such as silicon and metals (1), polymeric materials such as polydimethylsiloxane (2), and parylenes (3) together with advancements in flow regulation (4, 5) have made it possible to manufacture complex chip structures for a wide range of applications, including chemical kinetics (6), computations (7), and chemical analysis (8).The ultimate fluidic device is one that can handle single molecules and colloid particles. Such devices require unprecedented control over transport and mixing behaviors, and to advance current fluidics into the single-molecule regime, we have to develop systems having physical dimensions in the nanometer scale. To create such devices, we can draw much knowledge from biological systems. For example, the Golgiendoplasmic reticulum network in eukaryotic cells has many attractive features for sorting and routing of single molecules, such as ultra-small-scale dimension, transport control, and capability to recognize different molecular species, and for performing chemical transformations in nanometer-sized compartments with minimal dilution. It is, however, extremely difficult to mimic these biological systems by using traditional microfabrication technologies and materials because of their small scale, complex geometries, and advanced topologies. Furthermore, it is difficult to implement traditional flow regulation methods on nanoscale systems.Our efforts are focused mainly on the development of soft microfabrication technologies for processing of fluid-state liquid crystalline bilayer membranes. These materials have unique mechanical properties allowing creation of nanoscale structures, such as spheres and tubes with extremely high curvatures (9). The geometry of such structures is governed by both selfassembling and self-organizing properties of the lipid membrane material and can be changed o...

Exocytosis is the fundamental process underlying neuronal communication. This process involves fusion of a small neurotransmitter-containing vesicle with the plasma membrane of a cell to release minute amounts of transmitter molecules. Exocytosis is thought to go through an intermediate step involving formation of a small lipid nanotube or fusion pore, followed by expansion of the pore to the final stage of exocytosis. The process of exocytosis has been studied by various methods; however, when living cells are used it is difficult to discriminate between the molecular effects of membrane proteins relative to the mechanics of lipid-membranedriven processes and to manipulate system parameters (e.g., membrane composition, pH, ion concentration, temperature, etc.). We describe the use of liposome-lipid nanotube networks to create an artificial cell model that undergoes the later stages of exocytosis. This model shows that membrane mechanics, without protein intervention, can drive expansion of the fusion pore to the final stage of exocytosis and can affect the rate of transmitter release through the fusion pore.