  We characterize the role of electrostatic fluctuations on the charge
selectivity of cylindrical nanopores confining electrolyte mixtures. To this
end, we develop an extended one-loop theory that can account for correlation
effects induced by the surface charge, nanoconfinement of the electrolyte, and
interfacial polarization charges associated with the low permittivity membrane.
We validate the quantitative accuracy of the theory by comparisons with
previously obtained Monte-Carlo simulation data from the literature, and
scrutinize in detail the underlying forces driving the ionic selectivity of the
nanopore. In the biologically relevant case of electrolytes with divalent
cations such as CaCl2 in negatively charged nanopores, electrostatic
correlations associated with the dense counterion layer in the channel result
in an increase of the pore coion density with the surface charge. This
peculiarity analogous to the charge inversion phenomenon remains intact for
dielectrically inhomogeneous pores, which indicates that the effect should be
observable in nanofiltration membranes or DNA-blocked nanopores characterized
by a low membrane permittivity. Our results show that a quantitatively accurate
consideration of correlation effects is necessary to determine the ionic
selectivity of nanopores in the presence of electrolytes with multivalent
counterions.
