Nernst–Planck/Poisson model for the potential response of permselective gold nanopores

The recent introduction of ionophore-modified nanopores opened a new route for the fabrication of ion-selective electrodes with unique advantages. With this prospect we studied the potential response of modified and unmodified permselective gold nanopores obtained by electroless gold plating in the pores of track etched polycarbonate membranes. Anion and cation permselective membranes were synthesized by chemical modification of gold nanopores with thiol derivatives bearing either quaternary ammonium or sulfonate functionality, respectively. In all cases a good correlation was found between the experimental potential responses and numerical solutions of the Nernst–Planck/Poisson equation obtained by finite-element simulation. Similar to conventional polymeric ion-exchanger electrodes a co-ion interference region, i.e., Donnan failure, was found at high concentration regime that was exploited theoretically to estimate the surface charge density on the gold nanopores. Depending on the modification of the pore interior surface charge densities in the range of ca. +5 to −40 mC/m2 were found. Together with confirming the potential generating mechanism the effect of the pore diameter and surface charge density of the nanoporous membranes on the potential response is discussed in detail.