Mechanosensitive ion transport through hexagonal boron nitride nanopores

Biological nanopores are tiny channels embedded in cell membranes that shuttle ions and small molecules in and out of cells with astonishing precision and speed, serving as highly sensitive sieves that control fundamental life processes. Human-made nanopores in thin solid-state membranes, inspired by biology, promise to revolutionize applications such as DNA sensing and water desalination.

When the membrane material is just one atom thick (a so-called 2D material), ultra-precise nanopores can be made by selectively removing atoms one by one. In the case of the 2D material boron nitride, where atoms are arranged in a hexagonal pattern in the single layer, triangular nanopores can be created that are lined with nitrogen atoms and carry an overall negative charge.

The shape and chemical structure enables unique and precise interactions with ions and small molecules inside the pore. It is also predicted that the passage of ions through these nanopores can be precisely controlled by stretching the 2D material to a strain level of just a few percent. This project will explore the unique transport properties of these atomically precise nanopores in hexagonal boron nitride under varying amounts of strain, laying the foundations for advanced tunable filtration devices rivaling biological systems.

Theory and computer simulations will be used to model the transport processes, and experiments will be conducted to investigate the predicted phenomena using a specially designed fluid cell. Undergraduate and graduate students will be provided opportunities to engage in cutting-edge research in nanoscience and engineering. There will also be targeted outreach with K-12 STEM summer program participants in the California Central Valley region.

This project will explore mechanosensitive transport in crown ether-like nanopores in monolayer hexagonal boron nitride (h-BN). These pores will be fabricated by site-selective and dose-controlled electron and ion beam drilling in a transmission electron microscope/ion microscope chamber. After drilling, the pores will be mounted into a custom-built fluid cell that enables the controlled application of membrane strain using hydrostatic pressure as well as simultaneous voltage bias application and current measurements.

This setup will be used to characterize the nanopore baseline conductance, pore ion selectivity, and ion transport activation energies, as well as the response of these parameters to the applied membrane strain. These measurements will also characterize pore differential selectivity as a function of applied strain and will be coupled with analytical estimates and molecular dynamics simulations of stress-induced ion selectivity in an integrated make-measure-model cycle.

Theory and simulations will account for the charge distribution on the nanopore as well as polarization interactions of the ions with the pore. Theory and simulations will also produce a model for predicting pore selectivity in binary mixtures, which will be directly tested in the experiment. The main contributions of the project will center on demonstrating mechanosensitive transport in hB-N nanopores, exploring strain-tuned differential ion selectivity and ion transport gating in these nanopores, and understanding the fundamental mechanisms of the strain sensitivity of ion transport in 2D material nanopores.

Overall, this study will take the initial important steps toward engineering precise interfacial systems with dynamically reconfigurable separation performance.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.