Coupling of Electrostatic Interactions and Electroosmotic Flow in the Translocation of a Single-Stranded RNA through Charged Nanopores

The electric-field-driven translocation of charged biopolymers, such as single-stranded RNA (ssRNA), through charged nanopores is important for many biotechnology applications. However, the translocation dynamics is complex and influenced by the interplay of intra- and extra-chain electrostatic interactions (ESIs) and electroosmotic flow (EOF) inside the nanopore. To understand the coupling mechanisms of these three factors that govern the ssRNA translocation behavior, simulations are conducted by systematically varying both the salt concentration and nanopore surface charge density. First, we find that a reduction of the intrachain ESI, which solely depends on the salt concentration, facilitates the translocation. Second, while both the extra-chain ESI and EOF are governed by the nanopore charges and can exert similar effects on the translocation, their dependencies on the salt concentration exhibit opposite influences, especially at low salt concentrations. These aspects create a complex coupling and thus lead to diverse translocation behaviors.