Dehydration as a Universal Mechanism for Ion Selectivity in Graphene and Other Atomically Thin Pores

TL;DR

This paper demonstrates that dehydration alone can cause ion selectivity in atomically thin graphene pores, providing a fundamental mechanism that explains ion channel selectivity and has implications for filtration and bioengineering.

Contribution

The study reveals dehydration as a measurable, geometry-dependent mechanism for ion selectivity in graphene, extending to all ions and offering a new paradigm for understanding and engineering selectivity.

Findings

Dehydration alone causes measurable K+ over Cl- selectivity in graphene.

Dehydration-based selectivity applies to all ions, including cation over cation.

This mechanism explains conflicting experimental results and aids in designing selective filters.

Abstract

Ion channels play a key role in regulating cell behavior and in electrical signaling. In these settings, polar and charged functional groups -- as well as protein response -- compensate for dehydration in an ion-dependent way, giving rise to the ion selective transport critical to the operation of cells. Dehydration, though, yields ion-dependent free-energy barriers and thus is predicted to give rise to selectivity by itself. However, these barriers are typically so large that they will suppress the ion currents to undetectable levels. Here, we establish that graphene displays a measurable dehydration-only mechanism for selectivity of $\mathrm{K}^+$ over $\mathrm{Cl}^-$. This fundamental mechanism -- one that depends only on the geometry and hydration -- is the starting point for selectivity for all channels and pores. Moreover, while we study selectivity of $\mathrm{K}^+$ over $\mathrm{Cl}^-$, we find that dehydration-based selectivity functions for all ions, i.e., cation over cation selectivity (e.g., $\mathrm{K}^+$ over $\mathrm{Na}^+$). Its likely detection in graphene pores resolves conflicting experimental results, as well as presents a new paradigm for characterizing the operation of ion channels and engineering molecular/ionic selectivity in filtration and other applications.