Figure 6.

Molecular mechanism of ionic current modulation by a graphene nanopore capacitor. (a) Profiles of the electrostatic potential along the nanopore axis for the five conductance states of the nanopore capacitor. The background image showing the outline of the nanopore capacitor is aligned with the z coordinate. Each electrostatic profile was obtained by averaging instantaneous distributions of the electrostatic potentials over the frames of the respective MD trajectory (see Methods). All potentials shown were obtained from the simulations performed under a transmembrane bias of 500 mV. (b) Local density (red color scale) and local velocity (streamlines) of K⁺ (left) and Cl⁻ (right) ions in the baseline state of the nanopore capacitor, which is schematically indicated by the dark grey circles, at a 200 mV transmembrane bias. The maps show the x − z cross section of the corresponding three-dimensional density and velocity fields. The maps were obtained by averaging over the corresponding MD trajectories and radially with respect to the nanopore axis. The solid-state membrane is not shown for clarity. (c) Same as panel b but for the K⁺ conducting state of the nanopore capacitor. The blue circles schematically indicate the negative charge of the graphene sheets. (d) The relative contribution of the surface and bulk currents to the total ionic current for the five conductance states of the graphene nanopore capacitor. The horizontal dashed line indicates the ratio of the volume of the solution located within 0.6 nm from the nanopore surface to the entire volume of the nanopore. (e,f) Same as panel b but for the Enhanced and Off states of the nanopore capacitor. The red and blue circles indicate the charge (positive or negative, respectively) of the graphene layers.