An array of aligned carbon nanotubes (CNTs) was incorporated across a polymer film to form a well-ordered nanoporous membrane structure. This membrane structure was confirmed by electron microscopy, anisotropic electrical conductivity, gas flow, and ionic transport studies. The measured nitrogen permeance was consistent with the flux calculated by Knudsen diffusion through nanometer-scale tubes of the observed microstructure. Data on Ru(NH3)6(3+) transport across the membrane in aqueous solution also indicated transport through aligned CNT cores of the observed microstructure. The lengths of the nanotubes within the polymer film were reduced by selective electrochemical oxidation, allowing for tunable pore lengths. Oxidative trimming processes resulted in carboxylate end groups that were readily functionalized at the entrance to each CNT inner core. Membranes with CNT tips that were functionalized with biotin showed a reduction in Ru(NH3)6(3+) flux by a factor of 15 when bound with streptavidin, thereby demonstrating the ability to gate molecular transport through CNT cores for potential applications in chemical separations and sensing.

This paper describes a new class of composite materials designed by combining multiwall carbon nanotubes (MWNTs) and sol−gels. These materials provide new capabilities for the development of electrochemical devices by taking advantage of the favorable electrochemical characteristics of MWNTs. Further, variations in the silane precursors used and in the carbon nanotube content of the composites results in materials with a range of capacitance, electron-transfer rates, and potential to control selectivity.

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Synthetic nanopore membranes can be used to mimic ion channels provided that molecular transport through membranes is precisely gated with selective and reversible chemical interactions. Aligned nanotubes of carbon or other inorganic materials can be assembled to construct higher-order supramolecular architectures using polymer films to force chemical flux through hollow cores. Open tips of carbon nanotubes (CNT) can be activated to have carboxylic groups, which can be easily derivatized with a molecule that binds to a bulky receptor that can open/close the pore entrance. In particular, the core entrances of an aligned CNT membrane were functionalized with a desthiobiotin derivative that binds reversibly to streptavidin, thereby enabling a reversible closing/opening of the core entrance. Ionic flux through the CNT membrane was monitored using optically absorbing charged marker molecules. The flux is reduced by a factor of 24 when the desthiobiotin on the CNT is coordinated with streptavidin; release of streptavidin increases the flux, demonstrating a reversible ion-channel flow. Analysis of solutions of released streptavidin shows approximately 16 bound streptavidin molecules per CNT tip.

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