Mechanosensitive ion transport through hexagonal boron nitride nanopores

生物纳米孔是嵌入细胞膜的微小通道，以惊人的精度和速度将离子和小分子送入和传出细胞，充当控制基本生命过程的高度敏感的筛子。在生物学的启发下，在薄固态薄膜中制造的纳米孔有望给DNA传感和海水淡化等应用带来革命性的变化。当膜材料只有一个原子厚度时(即所谓的2D材料)，可以通过选择性地逐个去除原子来制造超精密纳米孔。在2D材料氮化硼的情况下，原子在单层中以六角形图案排列，可以创建排列有氮原子并携带整体负电荷的三角形纳米孔。其形状和化学结构使其能够与孔内的离子和小分子进行独特而精确的相互作用。据预测，通过将2D材料拉伸到只有几个百分点的应变水平，就可以精确地控制离子通过这些纳米孔的过程。该项目将探索这些原子精确的纳米孔在不同应变下在六方氮化硼中的独特传输特性，为先进的可调过滤设备与生物系统相媲美奠定基础。将使用理论和计算机模拟来模拟传输过程，并将使用专门设计的流体室进行实验来研究预测的现象。本科生和研究生将有机会从事纳米科学和工程领域的前沿研究。该项目还将与加州中央山谷地区的K-12 STEM夏季项目参与者进行有针对性的接触。该项目将探索单层六方氮化硼(h-BN)中冠醚状纳米孔的机械敏感传输。这些孔将通过在透射式电子显微镜/离子显微镜小室中进行位置选择和剂量控制的电子束和离子束钻孔来制造。钻孔后，孔将被安装到定制的流体单元中，该单元可以使用流体静压控制膜应变的施加，以及同时施加电压和电流测量。该装置将用于表征纳米孔基线电导、孔道离子选择性和离子传输活化能，以及这些参数对施加的膜应变的响应。这些测量还将表征作为施加应变的函数的孔差选择性，并将与应力诱导离子选择性的分析估计和分子动力学模拟结合在一个综合的制造-测量-模型循环中。理论和模拟将考虑纳米孔上的电荷分布以及离子与孔的极化相互作用。理论和模拟还将产生一个预测二元混合物中孔选择性的模型，该模型将在实验中直接进行测试。该项目的主要贡献将集中在展示HB-N纳米孔中的机械敏感输运，探索应变调谐的微分离子选择性和离子输运门控，以及理解二维材料纳米孔中离子输运应变敏感性的基本机制。总体而言，这项研究将朝着设计具有动态可重构分离性能的精确界面系统迈出重要的第一步。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.