Department of Chemistry and ‡MOAC Doctoral Training Centre, University of Warwick , Coventry, U.K. CV4 7AL.
J Am Chem Soc. 2014 Oct 1;136(39):13735-44. doi: 10.1021/ja506139u. Epub 2014 Sep 19.
Nanopipettes are emerging as simple but powerful tools for probing chemistry at the nanoscale. In this contribution the use of nanopipettes for simultaneous surface charge mapping and topographical imaging is demonstrated, using a scanning ion conductance microscopy (SICM) format. When a nanopipette is positioned close to a surface in electrolyte solution, the direct ion current (DC), driven by an applied bias between a quasi-reference counter electrode (QRCE) in the nanopipette and a second QRCE in the bulk solution, is sensitive to surface charge. The charge sensitivity arises because the diffuse double layers at the nanopipette and the surface interact, creating a perm-selective region which becomes increasingly significant at low ionic strengths (10 mM 1:1 aqueous electrolyte herein). This leads to a polarity-dependent ion current and surface-induced rectification as the bias is varied. Using distance-modulated SICM, which induces an alternating ion current component (AC) by periodically modulating the distance between the nanopipette and the surface, the effect of surface charge on the DC and AC is explored and rationalized. The impact of surface charge on the AC phase (with respect to the driving sinusoidal signal) is highlighted in particular; this quantity shows a shift that is highly sensitive to interfacial charge and provides the basis for visualizing charge simultaneously with topography. The studies herein highlight the use of nanopipettes for functional imaging with applications from cell biology to materials characterization where understanding surface charge is of key importance. They also provide a framework for the design of SICM experiments, which may be convoluted by topographical and surface charge effects, especially for small nanopipettes.
纳米移液器作为一种在纳米尺度探测化学物质的简单而强大的工具正在兴起。本研究展示了使用纳米移液器以扫描离子电导显微镜（SICM）的形式同时进行表面电荷测绘和形貌成像。当纳米移液器靠近电解质溶液中的表面时，施加在纳米移液器中的准参比对电极（QRCE）和溶液中的第二个 QRCE 之间的偏压驱动的直接离子电流（DC）对表面电荷敏感。电荷灵敏度源于纳米移液器和表面之间的扩散双电层相互作用，产生一个具有选择性的区域，在低离子强度下（本文中为 10mM1:1 水溶液）变得越来越重要。这导致了随着偏压变化的极性相关离子电流和表面诱导整流。通过距离调制 SICM，通过周期性调制纳米移液器和表面之间的距离来诱导交替离子电流分量（AC），研究了表面电荷对 DC 和 AC 的影响并进行了合理化。特别强调了表面电荷对 AC 相位（相对于驱动正弦信号）的影响；这个量的变化对界面电荷非常敏感，并为同时进行形貌和电荷成像提供了基础。本文的研究强调了纳米移液器在从细胞生物学到材料特性分析等领域的功能成像中的应用，因为了解表面电荷是非常重要的。它们还为 SICM 实验的设计提供了一个框架，特别是对于小的纳米移液器，这些实验可能会受到形貌和表面电荷效应的影响。
