Numerical Modeling of the Bistability of Electrolyte Transport in Conical Nanopores

In this paper, we present a numerical model of the bistability in ionic conductivity in conical nanopores. Our laboratory has previously reported experimental observations of unusual bistable electrolyte transport phenomena when a conical nanopore filled with a high conductive electrolyte solution (i.e., 5 mM KCl aqueous solution) was immersed in a low conductive electrolyte solution (i.e., 5 mM KCl in dimethyl sulfoxide (DMSO)/water). At a constant positive pressure across the nanopore (internal vs. external) and slowly increasing negative voltage, a sudden drop of current occurred within a few hundred milliseconds at a critical voltage. The current drop indicates a rapid transition between two conductivity states, or a bistability of electrolyte transport. A steady-state model based on the Nernst-Planck equation, Navier-Stokes equation and Poisson's equation using COMSOL Multiphysics successfully reproduced the bistability observed in experiments. Investigation of the mechanism of the bistability suggests the presence of a positive feed-back loop coupling fluid flow and ion distributions, causing a sharp transition between two conductivity states.