A numerical study of the selectivity of an isolated cylindrical or conical nanopore to a charged macro-ion.

The selectivity of a single nanopore in a uniformly charged solid membrane to a charged analyte ion is studied using numerical simulation. A continuum model is used where the ions are regarded as point particles and characterized by a continuously varying number density. The problem is described by the coupled equations for the electrostatic potential, ion-transport, and hydrodynamic flow, which are solved under appropriate boundary conditions using a finite volume method. The nanopore geometry is considered conical, the cylindrical pore being a special case where the cone angle is zero. The selectivity is characterized by a dimensionless parameter: the pore selectivity index. Results are presented showing how the pore selectivity index varies with the membrane surface charge and other parameters of the problem. The role of hydrodynamic flow on transport properties is examined and found to be consistent with theoretical results on electroosmotic flow through nanopores.