Synthetic nanopores with fixed charges: an electrodiffusion model for ionic transport

Synthetic nanopores with fixed charges exhibit ionic equilibrium and transport properties that resemble those displayed by biological ion channels. We present an electrodiffusion model based on the Nernst-Planck flux equations, which allows for a qualitative description of the steady state ionic transport through a nanopore when the membrane fixed charges and all mobile carriers (including the water ions) are properly taken into account. In particular, we study the current-voltage curve, the electrical conductance, the reversal potential (a measure of the nanopore ionic selectivity), as well as the flux inhibition by protons and divalent cations in the nanopore. The model clearly shows how the changes in the ionization state of the fixed charges with pH and salt concentration dictate the electrical properties of the nanopore. The agreement between the model predictions and previous experimental data allows us to identify which are the main characteristics that permit a simple description of this complex system.