Electrostatic Gating of Ionic Conductance Through Heterogeneous van der Waals Nanopores

TL;DR

This paper presents ionic transistors with sub 10 nm vdW heterostructure nanopores that achieve significant current modulation at low voltages and physiological salt levels, advancing nanofluidic device applications.

Contribution

The study introduces a novel ionic transistor design using vdW heterostructure nanopores with internal graphene gates, enabling low-voltage operation at higher ionic strengths.

Findings

Up to 10-fold current modulation at 0.3 V gate voltage in 10 mM KCl

2-fold modulation at 100 mM KCl

Surface charge and electrochemical asymmetry govern device behavior

Abstract

Nanofluidic ionic transistors typically require gate voltages above 1 V and operate only at sub millimolar ionic strengths, limiting their biocompatible applications. We demonstrate ionic transistors consisting of single sub 10 nm nanopores drilled in van der Waals (vdW) heterostructures with internal gate electrodes made of few layer graphene. These devices deliver up to 10fold current modulation at gate voltages as low as 0.3 V in 10 mM KCl, and 2fold modulation at near physiological 100 mM KCl. Baseline conductance with no gate shows surface charge dominated transport below 100 mM KCl consistent with negatively charged hBN walls and 5 nm opening of the pores. The surface charge and the electrochemical asymmetry introduced by the three electrode configuration govern the device behavior: negative gate voltage (VG) enriches ionic concentrations and enhances current, whereas positive VG induces a local depletion zone that suppresses transport. The current modulation by VG is dependent on the polarity of the transmembrane potential and leads to ion current rectification. Molecular dynamics simulations of a nanopore in a hBN graphene hBN stack reveal confinement and surface charge dependent suppression of relative permittivity of interfacial water. Continuum modeling with radially varying interfacial water permittivity reproduces the asymmetric IV characteristics and explains how the embedded gate sculpts local potential and ion concentrations. By enabling sub 0.5 V control of ionic transport at up to 100 mM salt concentrations, these devices address a key barrier in nanofluidics and open the pathway to low power ionic circuits and biosensing.