Abnormal Ionic-Current Rectification Caused by Reversed Electroosmotic Flow under Viscosity Gradients across Thin Nanopores.
Abnormal Ionic-Current Rectification Caused by Reversed Electroosmotic Flow under Viscosity Gradients across Thin Nanopores.
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DOI：
10.1021/acs.analchem.8b04225
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发表时间：
2018-11
影响因子：
7.4
通讯作者：
Yinghua Qiu;Z. Siwy;M. Wanunu
中科院分区：
文献类型：
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作者：
Yinghua Qiu;Z. Siwy;M. Wanunu
单纳米孔由于其广泛的应用而吸引了许多科学兴趣。大多数实验都是在纳米孔与膜两侧的相同电解质接触的情况下进行的，尽管在自然系统中，穿过半透膜的溶液梯度是无处不在的。在这篇手稿中，我们研究了离子和流体运动通过薄纳米孔粘度梯度下的实验和模拟。在这些条件下观察到离子电流整流，因为具有不同电导率的溶液在电渗流引起的不同偏压下填充穿过孔。我们发现，充满高粘度的解决方案的孔表现出的电流增加与所施加的电压在一个陡峭的斜率超过阈值电压，这异常降低了电流整流比。通过模拟，我们发现，反向电渗流，填充孔与较低粘度的水溶液，是负责这种行为。反向电渗流可以解释为沿着孔的共离子比抗衡离子消耗得慢。通过增加孔表面的表面电荷密度，电流整流比可以达到穿过薄纳米孔的粘度梯度的值。我们的研究结果揭示了在进行跨纳米孔和纳米流体通道的粘度梯度实验时要考虑的基本方面。
Single nanopores have attracted much scientific interest because of their versatile applications. The majority of experiments have been performed with nanopores being in contact with the same electrolyte on both sides of the membrane, although solution gradients across semipermeable membranes are omnipresent in natural systems. In this manuscript, we studied ionic and fluidic movement through thin nanopores under viscosity gradients both experimentally and using simulations. Ionic-current rectification was observed under these conditions because solutions with different conductivities filled across the pore under different biases caused by electroosmotic flow. We found that a pore filled with high-viscosity solutions exhibited a current increase with applied voltage in a steeper slope beyond a threshold voltage, which abnormally reduced the current-rectification ratio. Through simulations, we found that reversed electroosmotic flow, which filled the pore with aqueous solutions of lower viscosities, was responsible for this behavior. The reversed electroosmotic flow could be explained by slower depletion of co-ions than of counterions along the pore. By increasing the surface charge density of pore surfaces, current-rectification ratio could reach the value of the viscosity gradient across thin nanopores. Our findings shed light on fundamental aspects to be considered when performing experiments with viscosity gradients across nanopores and nanofluidic channels.