Potentiometric Studies on Ion-Transport Selectivity in Charged Gold Nanotubes.

Under ideal conditions, nanotubes with a fixed negative tube-wall charge will reject anions and transport-only cations. Because many proposed nanofluidic devices are optimized in this ideally cation-permselective state, it is important to know the experimental conditions that produce ideal responses. A parameter called C, the highest salt concentration in a contacting solution that still produces ideal cation permselectivity, is of particular importance.

Effect of Organic Cation Adsorption on Ion-Transport Selectivity in a Cation-Permselective Nanopore Membrane.

A key knowledge gap in the emerging field of nanofluidics concerns how the ionic composition and ion-transport properties of a nanoconfined solution differ from those of a contacting bulk solution. We and others have been using potentiometric concentration cells, where a nanopore or nanotube membrane separates salt solutions of differing concentrations to explore this issue. The membranes studied contained a fixed pore/tube wall anionic charge, which ideally would prohibit anions and salt from entering the pore/tube-confined solution.

Chemical Sensing and Chemoresponsive Pumping with Conical-Pore Polymeric Membranes.

Synthetic membranes containing asymmetrically shaped pores have been shown to rectify the ionic current flowing through the membrane. Ion-current rectification means that such membranes produce nonlinear current-voltage curves analogous to those observed with solid-state diode rectifiers. In order to observe this ion-current rectification phenomenon, the asymmetrically shaped pores must have pore-wall surface charge.