Department of Physics, North Carolina State University, Raleigh, NC 27695, United States of America.
Nanotechnology. 2019 Oct 11;30(41):41LT01. doi: 10.1088/1361-6528/ab31f7. Epub 2019 Jul 13.
Nanofluidic devices have channel dimensions which come to within one order of magnitude of the Debye length of common aqueous solutions. Conventionally, external driving is used to create concentration polarization of ions and biomolecules in nanofluidic devices. Here we show that long-range ionic strength gradients intrinsic to all nanofluidic devices, even at equilibrium, also drive a drift of macromolecules. To demonstrate the effect, we confine long DNA to straight nanochannels of constant, rectangular cross-section (100 × 100 nm) which are connected to large microfluidic reservoirs. The motion of DNA is observed in absence of any driving. We find that at low ionic strengths, molecules in nanochannels migrate toward the nano-micro interface, while they are undergoing purely diffusive motion in high salt. Using numerical models, we demonstrate that the motion is consistent with the ionic strength gradient at the micro-nano interface even at equilibrium, and that the dominant cause of the drift is diffusophoresis.
纳米流控装置的通道尺寸与常见水溶液的德拜长度相差一个数量级。传统上，外部驱动力用于在纳米流控装置中产生离子和生物分子的浓度极化。在这里，我们表明，即使在平衡状态下，所有纳米流控装置固有的长程离子强度梯度也会导致大分子的漂移。为了证明这一效果，我们将长 DNA 限制在具有恒定矩形横截面（100×100nm）的直纳米通道中，这些通道与大型微流控储液器相连。在没有任何驱动力的情况下观察 DNA 的运动。我们发现，在低盐度下，纳米通道中的分子朝着纳米-微界面迁移，而在高盐度下，它们处于纯扩散运动状态。使用数值模型，我们证明即使在平衡状态下，分子的运动也与微纳米界面处的离子强度梯度一致，并且漂移的主要原因是扩散电泳。
