Molecular Transport across the Ionic Liquid-Aqueous Electrolyte Interface in a MoS Nanopore.

Nanopore sequencing of DNA has been enabled by the use of a biological enzyme to thread DNA through an engineered biological nanopore while recording the ionic current flowing through the nanopore. Efforts to realize a similar concept using a solid-state nanopore have been met with several technical challenges, one of which is the high speed of DNA translocation and the other the low ionic current contrast among individual nucleotides. A promising avenue to addressing both problems is using an ionic liquid to slow DNA translocation and a tiny nanopore in the MoS membrane to distinguish individual nucleotides. The physical mechanisms enabling these technical advances have remained elusive. Here, we characterize the ion and DNA transport through the ionic liquid/aqueous electrolyte interface, with and without a MoS nanopore, using the all-atom molecular dynamics method. We find that the partial miscibility of the ionic liquid and the aqueous electrolyte considerably alters the physics of the nanopore translocation process. Thus, the interface of the two phases generates a contact potential of 600 mV, the ionic current is dominated by the motion of ionic liquid molecules through the aqueous solution phase, and the DNA nucleotides exhibit preferential partitioning into the aqueous electrolyte, which leads to spontaneous transport of DNA polymers from the ionic liquid to the aqueous solution compartment in the absence of external voltage bias. The complex physics of the two-phase nanopore system offers a multitude of opportunities for extending the functionality of nanopore-sensing platforms.