Ion transport across solid-state ion channels perturbed by directed strain

Abstract

We combine quantum-chemical calculations and molecular dynamics simulations to consider aqueous ion flow across non-axisymmetric nanopores in monolayer graphene and MoS2. When the pore-containing membrane is subject to uniaxial tensile strains applied in various directions, the corresponding permeability exhibits considerable directional dependence. This anisotropy is shown to arise from directed perturbations of the local electrostatics by the corresponding pore deformation, as enabled by the pore edge geometries and atomic compositions. By considering nanopores with ionic permeability that depends on the strain direction, we present model systems that may yield a detailed understanding of the structure-function relationship in solid-state and biological ion channels. Specifically, the observed anisotropic effects potentially enable the use of permeation measurements across strained membranes to obtain directional profiles of ion-pore energetics as contributed by groups of atoms or even individual atoms at the pore edge. The resulting insight may facilitate the development of subnanoscale pores with novel functionalities arising from locally asymmetric pore edge features.

Pressure-Induced Enlargement and Ionic Current Rectification in Symmetric Nanopores

“…By monitoring the size of the nanopore while the membrane is undergoing pressure-induced blistering, we demonstrate that local strain in the membrane can be accurately measured. As these membranes are typically used as supports for 2D material nanopore measurements, this is the first step to measuring mechanosensitivity in 2D materials − as it allows calibration and controlled application of stresses. Stress in the 2D membrane under deformation is expected to cause restructuring of bonds in the nanopore edges, opening up pathways for ion transport, in direct analogy to biological ion channels .…”

“…3,4,26 Theoretical work on sub-nm pores in 2D materials indicates the presence of strong mechanosensitivity to lateral stresses. [27][28][29][30][31] To realize a truly mechanosensitive solid-state sensor, one which would mimic mechanosensitive biological channels, 32 one needs to first understand the elastic behaviour of nanopores in solid state membranes.…”

“…Blistering of thin membranes such as silicon nitride or blistering and delamination of 2D materials − has been extensively studied in dry conditions. Studies in liquid and with nanopores have so far been restricted to nanopores drilled in elastomeric membranes for studying analyte translocations. , No experiments have been performed to date with nanopores in elastic solid-state membranes, although such membranes are usually used in conditions of osmotic or hydraulic pressure gradients which could influence pore properties like ion selectivity and water permeability. ,, Theoretical work on subnanometer pores in 2D materials indicates the presence of strong mechanosensitivity to lateral stresses. − To realize a truly mechanosensitive solid-state sensor, one which would mimic mechanosensitive biological channels, one needs to first understand the elastic behavior of nanopores in solid state membranes.…”

Origin and control of ionic hydration patterns in nanopores

“…It is well-known that the structure of ionic hydration shells is one of the key factors controlling ionic permeation in nanopores [8,[15][16][17]. In confined geometries some of the water molecules are lost from the hydration shells, and the resultant dehydration barrier is the subject of extensive research [8,[17][18][19][20][21][22][23][24][25][26][27][28]. One outcome is an appreciation of the extraordinary complexity of the hydration patterns around an ion in the pore [18,22,29], as has been confirmed by numerous molecular dynamics (MD) simulations [5,8,22,30,31].…”

Field-Dependent Dehydration and Optimal Ionic Escape Paths for C2N Membranes

“… 41 The two mechanisms leading to field-induced barrier changes oppose the original bias field and consequently limit transport, providing yet another example of solvent screening at the nanoscale. Interestingly, field-induced asymmetry of hydration shells along the z direction may be combined with in-plane manipulation of the shells induced by directed membrane strains, 59 potentially yielding a path toward hybrid mechano-electric gating.…”