Figure 4.

Enhancement and reduction of ionic current by oppositely charged graphene plates. (a) Representative configuration of ions in a nanopore capacitor system that has oppositely charged graphene plates: σ_top = +2.0 e nm⁻² and σ_bottom = −2.0 e nm⁻²; the direction of the transmembrane bias aligns with the direction of electric field produced by the charged graphene sheets. The particular molecular configuration shown corresponds to a transmembrane bias of 200 mV. The vertical arrow indicated the direction of the electric field produced by the transmembrane bias. (b) The average concentration of Cl⁻ (solid) and K⁺ (dashed) ions along the pore axis at 0 mV (black), 200 mV (red), 500 mV (purple), and 1 V (yellow) transmembrane bias. The shaded region indicates a concentration below the bulk concentration of 1.1 M. (c) The total average concentration of K⁺ (striped) and Cl⁻ (solid) ions inside the nanopore at transmembrane biases of 0 mV (blue), 200 mV (red), 500 mV (purple), and 1000 mV (yellow). The average concentrations and the concentration profiles were obtained as described in the caption to Figure 2c,d. (d) The average ionic current (total height of each bar) and the currents carried by K⁺ (striped) and Cl⁻ (solid) species at 200 mV (red), 500 mV (purple), and 1 V (yellow) transmembrane bias. Error bars indicate the standard error of the mean. (e) The simulated conductance of the nanopore capacitor system versus the transmembrane bias. Data for the baseline (uncharged) capacitor are shown for comparison.(f–j). Same as panels a–e but for the opposite arrangement of the charged graphene plates: σ_top = −2.0 e nm⁻² and σ_bottom = +2.0 e nm⁻². In this system, the direction of the transmembrane bias is opposite to that of the electric field produced by the charged graphene sheets.