Ion transport through confined ion channels in the presence of immobile charges.

We study charge transport in an ionic solution in a confined nanoscale geometry in the presence of an externally applied electric field and immobile background charges. For a range of parameters, the ion current shows nonmonotonic behavior as a function of the external ion concentration. For small applied electric field, the ion transport can be understood from simple analytic arguments, which are supported by Monte Carlo simulations. The results qualitatively explain measurements of ion current seen in a recent experiment on ion transport through a DNA-threaded nanopore [D. J. Bonthuis, Phys. Rev. Lett, 97, 128104 (2006)].