Electrostatically Gated Trilayer Graphene Nanopore as an Ultrathin Rectifying Ion Filter.

Abstract

Biological ion channels have significant ion selectivity and rectification properties due to angstrom-scale selectivity filters, but it is challenging to develop artificial analogs. Nanopores in two-dimensional (2D) materials have presented various potential applications such as energy conversion, ion separation, and biosensing. Here, we report a subnanometer trilayer graphene (TLG) nanopore with a conical structure as a switchable biomimetic ion filter under electrostatic gating. The nanopores show high ion selectivity and rectified current-voltage characteristics. Electrostatic gating significantly enhances the rectification ratio to an ultrahigh value. The transmembrane voltage induces reversible conductance "on" and "off" states of the TLG nanopore, which simulates the action potentials in electrically excitable cells. Theoretical modeling reveals that the unique ion transport through the 1 nm thick conical channels is attributed to the contrasting overlapping intensity of the electrical double layers (EDL) at the <i>base</i> and <i>tip</i> of the TLG nanopore. Combined with the different internal inhomogeneous electric fields, this leads to a reversed rectification direction, distinct from conventional microscopical conical channels. This study suggests ways to develop ultrathin in vitro biomimetic devices for broad applications in energy conversion and biosensing.