Dual pH Gradient and Voltage Modulation of Ion Transport and Current Rectification in Biomimetic Nanopores Functionalized with a pH-Tunable Polyelectrolyte

The potential applications of biomimetic artificial nanopores in versatile fields capture much attention in the past few decades. Although it is known that applying simultaneously an electric potential and a pH gradient can improve appreciably the performance of the ion current rectification of a nanopore, the underlying mechanisms are still not understood comprehensively. Adopting a cylindrical nanopore functionalized with homogeneous (single) pH-tunable polyelectrolyte brushes, these mechanisms are discussed in this study. In particular, the roles that the applied pH, electric potential gradients, and the grafting density of the polyelectrolyte chains played are examined in detail. We show that homogeneously modified nanopores can also exhibit ion current rectification behavior that is only seen in nanopores functionalized with two or more kinds of polyelectrolytes. Several interesting results are also observed. For example, if the applied pH gradient is sufficiently strong, the preferential direction of the ionic current can be tuned by the level of the applied electric potential; if it is sufficiently weak, an increase in the grafting density of the polyelectrolyte chains can make that preferential direction reversed. These results provide not only explanation for the behaviors associated with the transport of ions in nanopores but also a reference for designing relevant devices