Understanding the potentiometric response of cation-permselective hydrophilic nanopore-based electrodes in the low ion concentration range

Abstract

Permselective membranes are at the core of important applications and devices, that include ion-selective electrodes, energy conversion, and separation. Here we report the potential response in the low ion concentration range of hydrophilic cation-permselective gold nanopore-based membranes obtained by surface modification with a sulfonate-bearing thiol derivative. Apart from conventional polymeric permselective membranes, we confirmed ‘equal’ potentiometric responses for the same valency cations, that include both inorganic and organic cations. A refined Nernst–Planck/Poisson (NPP) model to account for previously neglected mass transport effects in the low ion concentration domain was shown to accurately predict even the interesting zero current fluxes generated super-Nernstian responses for higher valency cations. For all investigated ions we found that their interaction with sulfonate-groups functionalized nanopores is dominantly electrostatic in its nature. Hence, the synthetic versatility of such permselective nanopores in conjunction with the possibility of a rational design of its properties based on the NPP model renders such nanopore-based membranes not only a convenient alternative to existent permselective membranes, but their unique properties show promises for novel ion-sensing and separation applications.