静电门控三层石墨烯纳米孔作为超薄整流离子过滤器

摘要：生物离子通道由于具有埃级别的选择性滤波器，因此具有显著的离子选择性和整流特性，但开发人工模拟物具有挑战性。二维（2D）材料中的纳米孔展现了多种潜在应用，如能量转换、离子分离和生物传感。本文，南方科技大学薛亚辉副教授、中国科学院重庆绿色智能技术研究王赟姣副研

1成果简介

生物离子通道由于具有埃级别的选择性滤波器，因此具有显著的离子选择性和整流特性，但开发人工模拟物具有挑战性。二维（2D）材料中的纳米孔展现了多种潜在应用，如能量转换、离子分离和生物传感。本文，南方科技大学薛亚辉副教授、中国科学院重庆绿色智能技术研究王赟姣副研究员、国家纳米科学中心涂斌副研究员等在《ACS Nano》期刊发表名为“Electrostatically Gated Trilayer Graphene Nanopore as an Ultrathin Rectifying Ion Filter”的论文，研究报道了一种具有锥形结构的亚纳米级三层石墨烯（TLG）纳米孔，作为可在静电栅控下切换的仿生离子滤波器。该纳米孔展现出高离子选择性和整流电流-电压特性。静电门控显著提升整流比至超高压值。跨膜电压诱导TLG纳米孔呈现可逆的导电“开”和“关”状态，模拟了电兴奋细胞中的动作电位。理论建模揭示，通过1纳米厚锥形通道的独特离子传输，归因于TLG纳米孔基部和尖端处电双层（EDL）重叠强度的对比。结合内部不均匀电场，这导致整流方向发生逆转，与传统微观锥形通道截然不同。本研究为开发超薄体外仿生装置提供了新思路，其在能量转换和生物传感等领域具有广泛应用前景。

2图文导读

图1. Biological inspiration and experimental setup. (a) Schematic illustration of a biological rectifying potassium channel with an asymmetric structure exhibiting an ∼1 nm region called the “selectivity filter” on one side for specific selection of K ions. (b) Cross-sectional schematics of the bioinspired ion filter based on a subnanometer conical nanopore in a CVD trilayer graphene nanopore membrane. The device was immersed in electrolyte solutions while ion currents were measured under different applied scanning voltages using Ag/AgCl electrodes. The inset shows dehydration of ions through a bioinspired ion filter. (c) Transmission electron microscopy (TEM) image of an ∼2 nm TLG nanopore. Scale bar: 5 nm.

图2. Rectified ion transport and ion selectivity. (a) Current–voltage (I–V) characteristics of several kinds of cations transported through the TLG nanopore of ∼0.78 nm diameter. All of the electrolyte solutions were maintained at 100 mM chloride concentrations and pH 7. (b) I–V curve for the graphene nanopore in a KCl solution with a concentration ratio of 1000. Cis was set to be 1 mM KCl solution, and trans had 1000 mM KCl solution. (c) Selectivity ratio Si of the graphene nanopore among different cations when the scanning voltage was −400 mV. The X-axis is ordered from the lowest to the highest cation hydration energy. (d) Rectification ratio of the TLG nanopore at various 100 mM cation-chloride solutions. (e) Conductance measurements as a function of the KCl concentration at pH 7. (f) Conductance measurements as a function of pH at 100 mM KCl solution (pH 2 to 12).

图3. Switchable rectification and transmembrane conductance through the TLG nanopore. (a) Cross-sectional schematics of the ion-gating experiment. The surface layer of TLG (the part not in contact with the electrolyte) on the silicon nitride substrate was connected to the external silver wires by conductive silver epoxy to apply a gate voltage (Vg) to the graphene. A pair of Ag/AgCl electrodes was used as source and drain bias (Vds) to monitor transmembrane ion currents (Ids). (b) Selectivity ratio Si of a ∼0.66 nm TLG nanopore among different cations when both Vds and Vg were −400 mV. The yellow marks a selectivity lower than 1 (K preference), while the blue background indicates a selectivity higher than 1 (Li preference). The X-axis is ordered from lowest to highest cation hydration energy. (c, d) Ion-gating behavior for an ∼0.51 nm nanopore device in 100 mM KCl at pH = 7. (c) I–V curves and (d) rectification ratio with V++g ranging from 0 mV to −400 mV. (e) (top) Reversible transmembrane ion current (Ids) of the device with (bottom) transmembrane voltage cycled between Vds = −400 mV (“ON” state) and Vds = 400 mV (“OFF” state) under the gate voltage (−400 mV). (f) Comparison of the rectification ratio of the subnanometer TLG nanopore and other reported graphene nanopores with different diameters in experiments. The open-circuit potential is abbreviated as the OCP.

图4. MD simulations and schematic illustration of the rectification mechanism in the ultrathin conical TLG nanopore. (a) MD simulations of local snapshots of K (red) and Cl+– (blue) through the subnanometer TLG nanopore. The hydration layer was significantly diminished due to the carbon of the graphene (gray) preventing the water molecules (cyan and white). The system was submerged in 100 mM KCl in the presence of driving electric fields. (b) I-E curve of the nanopore at different electric fields. (c, d) Distribution and transport direction of anions and cations at negative voltages (c) and positive voltages (d). tip region’s electrical double layer (EDL) yields significant overlap compared to the base region, resulting in more robust cation selectivity. The direction of the transmembrane potential induces enrichment and depletion of ions in the tip region (dashed box).

图5. Theoretical modeling of ion concentration and electric potential distributions in the TLG nanopore. (a–b) Concentration of potassium ion CK+ along the center symmetry axis z of the TLG nanopore in 100 mM KCl solution and the gray bar indicating the thickness of the nanopore. The z = 0.6 and −0.6 nm represent the nanopore’s tip end and base end. The electrostatic potential switches between the OCP (a) and Vg = −400 mV (b) when the Vds is −400 and 400 mV, respectively. (c, d) Numerical calculations of distributions of CK+ near the TLG nanopore in 100 mM KCl solution under the OCP (c) and Vg= −400 mV (d) when the Vds are −400 and 400 mV, respectively. Scale bars are 1 nm. (e, f) Distribution of electric potential ψ near the TLG nanopore in 100 mM KCl solution under the OCP (e) and Vg = −400 mV (f), when Vds is −400 and 400 mV, respectively. Scale bars are 1 nm.

3小结

综上所述，我们首次通过静电调控制备了具有锥形结构的TLG纳米孔，以模拟生物离子过滤器。该仿生离子通道展现出不对称的I-V特性和高离子选择性。TLG纳米孔的静电调控可有效调节离子传输，并在-400 mV的静电势下实现高达34的超高压整流比。值得注意的是，跨膜电压可作为快速开关激活纳米孔离子通道，类似于生物细胞膜的动作电位。通过理论建模揭示，约1纳米厚的锥形通道中独特的离子传输特性，源于纳米孔两端电双层（EDL）重叠差异以及锥形纳米孔内部的不均匀电场。本研究表明，石墨烯纳米孔为研究生物离子通道中超快且精确可控的离子传输机制，以及在单孔水平上工程化所需传输特性提供了有效平台。

文献：