Enhancement of charged macromolecule capture by nanopores in a salt gradient
Enhancement of charged macromolecule capture by nanopores in a salt gradient
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DOI：
10.1063/1.3170952
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发表时间：
2009-07-21
影响因子：
4.4
通讯作者：
Chou, Tom
中科院分区：
文献类型：
--
作者：
Chou, Tom
覆盖在合成膜上的纳米孔已被用作原理证明纳米流体应用的关键组件，特别是涉及生物分子操作或DNA测序的应用。操纵纳米孔附近的带电大分子的唯一实用方法是通过在跨越纳米孔的膜上施加电压差。然而，最近的实验表明，跨纳米孔施加盐浓度梯度也可以显著增强从纳米孔一端的低浓度带电分子库中捕获带电粒子。到目前为止，这种令人费解的效应一直没有得到物理上一致的理论解释。在这里，我们提出了一种增强捕获的电动机制，依赖于孔口附近的静电势。对于直径远大于局部屏蔽长度的长孔，我们得到了精确的解析表达式，说明了盐梯度如何控制局部电导率，从而导致局部静电势和带电分析物捕获率的增加。我们还发现，吸引人的静电势可能被向外的排斥电渗透流平衡，在某些情况下，电渗透流可以与盐梯度共谋，进一步提高分析物捕获率。
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 electro-osmotic flow that can in certain cases conspire with the salt gradient to further enhance the analyte capture rate.