Asymmetric properties of ion transport in a charged conical nanopore

Recently, the experimentally observed asymmetric properties of ion transport in charged conical nanopores (CCNs) that resemble those in biological ion channels have attracted a lot of attention in theoretical studies in nanotechnology research. In this paper, we report several tactics to study this effect by directly solving the Poisson-Nernst-Planck (PNP) equations. The result shows that PNP equations can indeed quantitatively describe the properties of these nanopores. Based on our numerical solutions, we contribute the rectification effect to ion-enrichment and ion-depletion. A detailed study of length dependence of current indicates that a relatively long length is indispensable for the CCNs to have rectification effect. We suggest that PNP equations and the calculation method could be further used to study other shapes of nanopores.