Transport of Water and Ions through a Graphene Nanopore in an Electric Field

Abstract

Graphene nanopore has been widely used in a nanofluidic device for sensing or analyzing biomolecules, as its single atom thickness provides high spatial resolution. The ionic conductance of nanopore is of primary importance for analyzing biomolecules transported through the pore. The continuum theory holds that conductance comprise of three contributions: bulk, surface (for a charged nanopore) and access ones. However, when the pore diameter approaches the size of the molecule, ion and water dynamics may deviate from the bulk values and continuum analysis cannot be used to account for experimental data. Here we perform molecular dynamics simulations to systematically investigate the relationship between conductance and the coupling transport of water and ions through a graphene nanopore in electric fields. The results show that the ionic conductance of nanopore strongly depend on the ionic conditions, including the salt concentration, ion mobility in the pore. More surprisingly, with the increase of the electric field strength, ion concentration in the nanopore sharply drops from the bulk concentration, while ion mobility in the nanopore increases. Ion mobility in the nanopore will decrease as the salt concentration in the nanopore is increased. These unordinary ion behaviors should be due to be a sum of three contributions: collision of ions, Wien effect, desolvation. The results presented here will be helpful not only in understanding the behavior of ions and water transport but also in the design of novel nanofluidic devices.