Department of Electrical and Computer Engineering, Seoul National University, Seoul 08826, Republic of Korea. (HLee)
Nanoscale. 2017 Aug 24;9(33):11871-11880. doi: 10.1039/c7nr02075a.
Over the past decade, nanofluidic diodes that rectify ionic currents (i.e. greater current in one direction than in the opposite direction) have drawn significant attention in biomolecular sensing, switching and energy harvesting devices. To obtain current rectification, conventional nanofluidic diodes have utilized complex nanoscale asymmetry such as nanochannel geometry, surface charge density, and reservoir concentration. Avoiding the use of sophisticated nano-asymmetry, micro/nanofluidic diodes using microscale asymmetry have been recently introduced; however, their diodic performance is still impeded by (i) low (even absent) rectification effects at physiological concentrations over 100 mM and strong dependency on the bulk concentration, and (ii) the fact that they possess only passive predefined rectification factors. Here, we demonstrated a new class of micro/nanofluidic diode with an ideal perm-selective nanoporous membrane based on ion concentration polarization (ICP) phenomenon. Thin side-microchannels installed near a nanojunction served as mitigators of the amplified electrokinetic flows generated by ICP and induced convective salt transfer to the nanoporous membrane, leading to actively controlled micro-scale asymmetry. Using this device, current rectifications were successfully demonstrated in a wide range of electrolytic concentrations (10 M to 3 M) as a function of the fluidic resistance of the side-microchannels. Noteworthily, it was confirmed that the rectification factors were independent from the bulk concentration due to the ideal perm-selectivity. Moreover, the rectification of the presenting diode was actively controlled by adjusting the external convective flows, while that of the previous diode was passively determined by invariant nanoscale asymmetry.
在过去的十年中，在生物分子传感、开关和能量收集装置中，对能整流离子电流（即一个方向的电流大于相反方向的电流）的纳米流体二极管引起了人们的极大关注。为了获得电流整流，传统的纳米流体二极管利用了复杂的纳米级不对称性，如纳米通道几何形状、表面电荷密度和储层浓度。避免使用复杂的纳米不对称性，最近引入了使用微尺度不对称性的微/纳米流体二极管；然而，它们的二极管性能仍然受到以下因素的限制：(i) 在生理浓度（超过 100mM）下，整流效果低（甚至不存在），并且强烈依赖于体浓度，以及 (ii) 它们仅具有被动的预定义整流因子。在这里，我们展示了一种基于离子浓度极化（ICP）现象的新型微/纳米流体二极管，它具有理想的选择性纳米多孔膜。在纳米结附近安装的薄侧微通道充当由 ICP 产生的放大电动流的缓解剂，并诱导对流盐转移到纳米多孔膜，从而导致主动控制的微尺度不对称性。使用该装置，在广泛的电解质浓度范围内（10M 至 3M）成功地演示了电流整流，这取决于侧微通道的流体阻力。值得注意的是，由于理想的选择性，整流因子与体浓度无关。此外，通过调节外部对流流，可主动控制提出的二极管的整流，而前一个二极管的整流则由不变的纳米级不对称性被动确定。
