Influences of Cone Angle and Surface Charge Density on the Ion Current Rectification Behavior of a Conical Nanopore

Due to its potential applications in biotechnology, ion current rectification (ICR) arising from the asymmetric nature of ion transport in a nanochannel has drawn the attention of researchers in various fields. Previous studies usually neglect the effects of osmotic and electroosmotic flows. In this study, a more general model taking account of these effects is adopted to describe the ICR behavior of a conical nanopore. The influences of the cone angle, surface charge density, and bulk salt concentration on this behavior are investigated, and mechanisms proposed to explain the results are obtained. We show that if the cone angle is enlarged by fixing the nanopore tip radius and raising its base radius, the ICR ratio has a local maximum. This behavior may not present if the cone angle is enlarged by fixing the nanopore base radius and raising its tip radius. The local maximum in the ICR ratio does not exist if the bulk salt concentration is sufficiently low or sufficiently high. This ratio also has a local maximum as the surface charge density varies, and the larger the cone angle, the higher the surface charge density at which the local maximum in the ICR ratio occurs.