Magnesium Ions Invert Selectivity and Electroosmotic Flow for Pristine Cation-Selective Nanopores

Nanopore sensing has emerged as a powerful technique for single molecule detection, utilizing changes in ionic current to identify molecules as they interact with a nanopore. The applied voltage driving this process also induces an electroosmotic flow (EOF). EOF can be employed to capture different analytes independently of their charge and hence be used for protein sensing and sequencing. In this study, we investigate the impact of divalent cations on EOF for biological nanopores (MspA, CytK, and their mutants) using molecular dynamics (MD) simulations and experiments. Our results reveal that divalent cations induce a decrease in both ionic current and EOF magnitude with respect to K+ in these cation-selective nanopores. This effect is caused by transient binding of divalent cations in the nanopore constriction, altering the effective surface charge of the nanopore and consequently modifying the cation/anion selectivity and the EOF.