Department of Electrical and Computer Engineering, Seoul National University, Seoul, 08826, Republic of Korea.
Department of Bioengineering, University of California, Berkeley, CA, 94720, USA.
Sci Rep. 2020 Jun 1;10(1):8898. doi: 10.1038/s41598-020-65433-y.
Perm-selective ion transportation in a nanoscale structure such as nanochannel, nanoporous membrane or nanojunction has been extensively studied with aids of nanofabrication technology for a decade. While theoretical and experimental advances pushed the phenomenon to seminal innovative applications, its basic observation has relied only on an indirect analysis such as current-voltage relation or fluorescent imaging adjacent to the nanostructures. Here we experimentally, for the first time, demonstrated a direct visualization of perm-selective ion transportation through the nanoscale space using an ionic plasma generation. A micro/nanofluidic device was employed for a micro bubble formation, plasma negation and penetration of the plasma along the nanojunction. The direct observation provided a keen evidence of perm-selectivity, i.e. allowing cationic species and rejecting anionic species. Furthermore, we can capture the plasma of lithium, which has lower mobility than sodium in aqueous state, passed the nanojunction faster than sodium due to the absence of hydrated shells around lithium. This simple, but essential visualization technique would be effective means not only for advancing the fundamental nanoscale electrokinetic study as well as interfacial ion transportation between liquid and plasma but also for providing the insight of new innovative engineering applications.
在纳米尺度结构（如纳米通道、纳米多孔膜或纳米结）中进行选择性离子传输的研究已经有十年了，纳米制造技术为此提供了广泛的支持。虽然理论和实验的进展推动了这一现象在开创性创新应用方面的发展，但对其基本观察仅依赖于间接分析，如纳米结构附近的电流-电压关系或荧光成像。在这里，我们首次通过离子等离子体的产生，在实验上直接观察到了通过纳米尺度空间的选择性离子传输。我们使用微/纳流控装置来形成微泡、中和等离子体并使等离子体沿着纳米结渗透。这种直接观察提供了选择性的敏锐证据，即允许阳离子物种通过，而排斥阴离子物种。此外，我们可以捕捉到等离子体中的锂离子，由于锂离子周围没有水合壳，因此它在水溶液中的迁移率比钠离子低，但比钠离子更快地通过纳米结。这种简单但基本的可视化技术不仅将成为推进基本的纳米尺度电动研究以及液体和等离子体之间界面离子传输的有效手段，而且还将为新的创新工程应用提供深入的了解。
