Physics Department, University of Arkansas, Fayetteville, AR 72701, USA.
Small. 2012 Feb 6;8(3):384-92. doi: 10.1002/smll.201290017.
An apparatus that integrates solid-state nanopore ionic current measurement with a scanning-probe microscope is developed. When a micrometer-scale scanning-probe tip is near a voltage-biased nanometer-scale pore (10–100 nm), the tip partially blocks the flow of ions to the pore and increases the pore access resistance. The apparatus records the current blockage caused by the probe tip and the location of the tip simultaneously. By measuring the current blockage map near a nanopore as a function of the tip position in 3D space in salt solution, the relative pore resistance increases due to the tip and ΔR/R0 is estimated as a function of the tip location, nanopore geometry, and salt concentration. The amplitude of ΔR/R0 also depends on the ratio of the pore length to its radius as Ohm's law predicts. When the tip is very close to the pore surface, ≈10 nm, experiments show that ΔR/R0 depends on salt concentration as predicted by the Poisson and Nernst–Planck equations. Furthermore, the measurements show that ΔR/R0 goes to zero when the tip is about five times the pore diameter away from the center of the pore entrance. The results in this work not only demonstrate a way to probe the access resistance of nanopores experimentally; they also provide a way to locate the nanopore in salt solution, and open the door to future nanopore experiments for detecting single biomolecules attached to a probe tip.
一种将固态纳米孔离子电流测量与扫描探针显微镜集成的仪器被开发出来。当一个微米级的扫描探针尖端靠近一个电压偏置的纳米级孔（10-100nm）时，尖端会部分阻挡离子流向孔，并增加孔的接入电阻。该仪器同时记录探针尖端引起的电流阻塞和尖端的位置。通过在盐溶液中测量纳米孔附近的电流阻塞图作为探针在 3D 空间中的位置的函数，相对孔电阻由于尖端而增加，并且ΔR/R0 作为尖端位置、纳米孔几何形状和盐浓度的函数来估计。ΔR/R0 的幅度也取决于孔的长度与半径的比值，正如欧姆定律所预测的那样。当尖端非常接近孔表面时，约为 10nm，实验表明，ΔR/R0 如泊松和能斯特-普朗克方程所预测的那样，取决于盐浓度。此外，测量结果表明，当尖端距离孔入口中心约五倍孔径时，ΔR/R0 趋于零。这项工作的结果不仅展示了一种实验探测纳米孔接入电阻的方法，还提供了一种在盐溶液中定位纳米孔的方法，并为未来用于检测附着在探针尖端上的单个生物分子的纳米孔实验开辟了道路。
