Proton enrichment and surface charge dynamics in pH-responsive nanopores Dominik Duleba and Robert Johnson University College Dublin, Ireland
The acid-disassociation of surface groups is crucial in nanopores as it generates the surface charge that drives fundamental nanoscale ion transport behaviors such as ion current rectification. The disassociation of surface groups is influenced by the local proton concentration which itself is dictated by the enrichment and depletion of ions in the conical nanopore as the voltage is changed. 1, 2 Despite this, most models of ion transport in conical nanopore systems assume a fixed surface charge and ignore localized pH changes. To study the dynamic interplay between the magnitudes and distributions of ion concentrations, pH distributions and surface charges, and its influence on the ion-current rectification as a function of electrolyte concentration, a finite element model that calculates the surface charge based on surface site density and local pH values was developed. This model additionally includes the water auto-ionization reaction and the subsequent shifting of the acidity constants at different positions within the nanopore geometry. The surface charge density was found to be non-linear across the nanopore and highly asymmetric between the different applied potentials, as well as highly influenced by the bulk pH and electrolyte concentrations. We demonstrate that our model qualitatively predicts experimental measurements of ion current rectification for different bulk pH values at the low electrolyte concentration regime. References 1. Yeh, L.-H.; Zhang, M.; Qian, S. Ion transport in a pH-regulated nanopore. Analytical chemistry 2013 , 85 (15), 7527-7534. 2. Atalay, S.; Yeh, L.-H.; Qian, S. Proton enhancement in an extended nanochannel. Langmuir 2014 , 30 (43), 13116-13120.
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