盐梯度中纳米孔增强带电大分子捕获
Enhancement of charged macromolecule capture by nanopores in a salt gradient
摘要：
跨越合成膜的纳米孔已被用作原理证明纳米流体应用中的关键组分，特别是涉及生物分子操纵或DNA测序的那些。操纵纳米孔附近的带电大分子的唯一实用方法是通过跨纳米孔膜施加的电压差。然而，最近的实验已经表明，跨纳米孔施加的盐浓度梯度也可以显著增强从纳米孔一端的带电分子的低浓度储库捕获带电粒子。这种令人困惑的效应至今还没有一个物理上一致的理论解释。在这里，我们提出了一个电动机制，这种增强的捕获依赖于附近的毛孔口的静电势。对于长孔直径远大于当地的筛选长度，我们得到准确的分析表达式，显示盐梯度如何控制当地的电导率，这可能会导致增加当地的静电势和带电的分析物捕获率。我们还发现，有吸引力的静电势可以通过向外的、排斥的电渗流（electrosovious flow，EEP）来平衡，所述电渗流可以在某些情况下与盐梯度合谋以进一步提高分析物捕获率。
英文摘要：
Nanopores spanning synthetic membranes have been used as key components in proof-of-principle nanofluidic applications, particularly those involving manipulation of biomolecules or sequencing of DNA. The only practical way of manipulating charged macromolecules near nanopores is through a voltage difference applied across the nanopore-spanning membrane. However, recent experiments have shown that salt concentration gradients applied across nanopores can also dramatically enhance charged particle capture from a low concentration reservoir of charged molecules at one end of the nanopore. This puzzling effect has hitherto eluded a physically consistent theoretical explanation. Here, we propose an electrokinetic mechanism of this enhanced capture that relies on the electrostatic potential near the pore mouth. For long pores with diameter much greater than the local screening length, we obtain accurate analytic expressions showing how salt gradients control the local conductivity which can lead to increased local electrostatic potentials and charged analyte capture rates. We also find that the attractive electrostatic potential may be balanced by an outward, repulsive electroosmotic flow (EOF) that can in certain cases conspire with the salt gradient to further enhance the analyte capture rate.
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