Electrokinetic-Flow Driven Rectification of Ion Current in a Tunable Polymer Nanopore

Ion current rectification (ICR) in a charged nanopore is a diode-like phenomenon, typically showing the distinct behaviors of the nanopore conductance, stemming from an accumulation and a depletion of ionic concentrations, when the voltage polarity is changed. This work experimentally study the importance of the solution properties like pH and salt concentration, and the concentration gradients applied across the nanopore on the ICR phenomenon in a tunable, polymer, conical nanopore. Results obtained show that the degree of ICR becomes significant when the salt concentration is low. In addition, the ICR behavior at the low solution pH is distinctly different from that at the high pH, resulting from the different charge nature of the polymer membrane. In contrast to the previous studies that using a combined organic and aqueous electrolyte solution to generate the ICR in a conical nanopore, we demonstrated that the ICR can be generated through an application of a salt concentration gradient in a pure aqueous solution by the electrokinetic flow (EKF). The ICR behaviors in the nanopore can be controlled by controlling the direction of the EKF in the nanopore.