Ion concentration polarization in polyelectrolyte-modified nanopores

Nanopores functionalized with synthetic or biological polyelectrolyte (PE) brushes have significant potentials to rectify ionic current and probe single biomacromolecules. In this work, electric-field-induced ion transport and the resulting conductance in a PE-modified nanopore are theoretically studied using a continuum-based model, composed of coupled Poisson-Nernst-Planck (PNP) equations for the ionic mass transport, and Stokes and Brinkman equations for the hydrodynamic fields in the exterior and interior of the PE layer, respectively. Because of the competition between the transport of counterions and co-ions in the nanopore, two distinct types of ion concentration polarization (CP) occur at either opening of the PE-modified nanopore. These distinct CP behaviors, which significantly affect the nanopore conductance, can be easily manipulated by adjusting the bulk salt concentration and the imposed potential bias. The induced CP in the PE-modified nanopore is more appreciable than that in the corresponding bare solid-state nanopore.