Modulation of ionic current rectification in short unipolar nanopores

With controlled ionic current rectification (ICR) achieved through a strategically designed non-uniform surface charge distribution, short unipolar nanopores exhibit promising applications in nanofluidic sensors, ionic circuits, and ion amplifiers. By systematically investigating how the charged length on inner pore walls modulates ion transport, we found that both the maximum ICR degree and the corresponding charged-length proportion were influenced by nanopore parameters and simulation conditions. For 100 nm-long unipolar nanopores, the highest ICR degree is obtained at a charged-length proportion of ∼0.3, due to the corresponding most significant ion enrichment and depletion inside the nanopore under opposite biases. This charged-length proportion of ∼0.3 consistently appears as a characteristic value across most considered cases. For short unipolar nanopores, the presence of exterior surface charges significantly enhances the ICR degree by facilitating ion transport through nanopores. The effective widths of charged regions beyond nanopore borders on outer surfaces exhibit direct proportionality to the pore diameter, surface charge density, and applied voltage, and inverse proportionality to the pore length and salt concentration. Our research may provide useful guidance for the design of unipolar nanopores and porous membranes incorporating such charge configurations.