Theoretical Division, MS-B213, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
J Phys Condens Matter. 2010 Nov 17;22(45):454126. doi: 10.1088/0953-8984/22/45/454126.
There has been tremendous experimental progress in the last decade in identifying the structure and function of biological pores (ion channels) and fabricating synthetic pores. Despite this progress, many questions still remain about the mechanisms and universal features of ionic transport in these systems. In this paper, we examine the use of nanopores to probe ion transport and to construct functional nanoscale devices. Specifically, we focus on the newly predicted phenomenon of quantized ionic conductance in nanopores as a function of the effective pore radius--a prediction that yields a particularly transparent way to probe the contribution of dehydration to ionic transport. We study the role of ionic species in the formation of hydration layers inside and outside of pores. We find that the ion type plays only a minor role in the radial positions of the predicted steps in the ion conductance. However, ions with higher valency form stronger hydration shells, and thus, provide even more pronounced, and therefore, more easily detected, drops in the ionic current. Measuring this phenomenon directly, or from the resulting noise, with synthetic nanopores would provide evidence of the deviation from macroscopic (continuum) dielectric behavior due to microscopic features at the nanoscale and may shed light on the behavior of ions in more complex biological channels.
在过去的十年中，人们在识别生物孔（离子通道）的结构和功能以及制造合成孔方面取得了巨大的实验进展。尽管取得了这些进展，但关于这些系统中离子传输的机制和普遍特征，仍有许多问题尚未解决。在本文中，我们研究了使用纳米孔来探测离子传输并构建功能纳米级设备。具体来说，我们专注于纳米孔中预测的量化离子电导现象作为有效孔径的函数——这一预测为探测脱水对离子传输的贡献提供了一种特别透明的方法。我们研究了离子种类在孔内外形成水合层中的作用。我们发现，离子类型在离子电导预测台阶的径向位置上只起很小的作用。然而，具有更高价态的离子形成更强的水合壳，因此提供了更明显的、因此更容易检测到的离子电流下降。用合成纳米孔直接测量这种现象，或者从由此产生的噪声中测量，将为由于纳米尺度上的微观特征而偏离宏观（连续）介电行为提供证据，并可能揭示离子在更复杂的生物通道中的行为。
