Electromodulated molecular transport in gold-nanotube membranes

We have developed a new class of synthetic membranes that contain monodisperse Au nanotubes with inside diameters of molecular dimensions (<1 nm). The Au nanotubes span the complete thickness of the membrane and can act as conduits for molecule and ion transport between solutions placed on either side of the membrane. We have recently become interested in the concept of electromodulating neutral molecule transport across these membranes. This communication describes a novel approach for accomplishing this objective. This approach makes use of an anionic surfactant which, when a positive potential is applied to the Au nanotube membrane, partitions into the nanotubes to charge the solution side of the electrical double layer at the tube walls. Because of the hydrophobic tail of the surfactant, this renders the nanotube interior hydrophobic, and the membrane now preferentially extracts and transports neutral hydrophobic molecules. Because the anionic surfactant can be expelled from the nanotubes by applying a negative potential, this provides a route for reversibly electromodulating neutral molecule transport in these membranes.