The Role of Nanopore Geometry for the Rectification of Ionic Currents

Conical nanopores from various materials (e.g., glass, silicon nitride, PET) were found to rectify ionic currents in electrolytes. Several models and simulations have been developed to explain and quantify this ion current rectification (ICR). In this Article, we apply numerical simulations based on the Poisson−Nernst−Planck equations to study the effect of pore size, electrolyte concentration, and half-cone angles on ICR at glass nanopore membranes. It is shown how the fixed charge on the glass surfaces overlaps with an externally applied transmembrane potential to yield a nonuniform potential distribution inside the pore. We also tried to assess the role of surface currents via the comparison of our numerical results with a simplified model. Surface conductivity seems to have only a weak influence on the total conductivity for pores with relatively low surface charges. Furthermore, our simulations show that for the occurrence of ICR the pore mouth radius r 0 has to be in the order of magnitude of the Debye length λ, but overlapping of the electrical double layers is not required. Also, the simple dimensionless ratio r 0/λ cannot solely be used quantify ICR. To show this in more detail, the role of the electrical double layer is discussed for different r 0/λ ratios and half-cone angles.