Revisiting the Origin of Nanopore Current Blockage for Volume Difference Sensing at the Atomic Level

Changes in the nanopore ionic current during entry of a target molecule underlie the sensing capability and dominate the intensity and extent of applications of the nanopore approach. The volume exclusion model has been proposed and corrected to describe the nanopore current blockage. However, increasing evidence shows nonconformity with this model, suggesting that the ionic current within a nanopore should be entirely reconsidered. Here, we revisit the origin of nanopore current blockage from a theoretical perspective and propose that the noncovalent interactions between a nanopore and a target molecule affect the conductance of the solution inside the nanopore, leading to enhanced current blockage. Moreover, by considering the example of an aerolysin nanopore discriminating the cytosine DNA and methylcytosine DNA that differ by a single methyl group, we completely demonstrate, by nanopore experiments and molecular dynamics simulations, the essential nature of this noncovalent interaction for discrimination. Our conductance model suggests multiplicative effects of both volume exclusion and noncovalent interaction on the current blockage and provides a new strategy to achieve volume difference sensing at the atomic level with highly specific current events, which would promote the nanopore protein sequencing and its applications in real-life systems.