Fachbereich Material-u. Geowissenschaften, Fachgebiet Materialanalytik, Technische Universität Darmstadt, Petersenstrasse 23, D-64287 Darmstadt, Germany.
J Am Chem Soc. 2010 Jun 23;132(24):8338-48. doi: 10.1021/ja101014y.
Molecular design of ionic current rectifiers created on the basis of single conical nanopores is receiving increasing attention by the scientific community. Part of the appeal of this topic relies on the interest in sensors and fluidic nanoactuators based on the transport of ions and molecules through nanopore architectures that can readily be integrated into functional systems. The chemical modification of the pore walls controls not only the diameter of these nanoarchitectures but also their selectivity and transport properties. In order to confer selectivity to solid-state nanopores, it is necessary to develop and explore new methods for functionalizing the pore walls. Hence, the creation of functional nanopores capable of acting as selective ion channels or smart nanofluidic sensors depends critically on our ability to assemble and build up molecular architectures in a predictable manner within confined geometries with dimensions comparable to the size of the building blocks themselves. In this context, layer-by-layer deposition of polyelectrolytes offers a straightforward process for creating nanoscopic supramolecular assemblies displaying a wide variety of functional features. In this work, we describe for the first time the integration of layer-by-layer polyelectrolyte assemblies into single conical nanopores in order to study and explore the functional features arising from the creation of charged supramolecular assemblies within the constrained geometry of the nanofluidic device. To address this challenging topic, we used a combined experimental and theoretical approach to elucidate and quantify the electrostatic changes taking place inside the nanopore during the supramolecular assembly process. The multilayered films were built up through consecutive layer-by-layer adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) on the pore surface. Our results show that the charge transport properties of single conical nanopores functionalized with PAH/PSS assemblies are highly dependent on the number of layers assembled on the pore wall. In contrast to what happens with PAH/PSS films deposited on planar surfaces (quantitative charge reversal), the surface charge of the pore walls decreases dramatically with the number of PAH/PSS layers assembled into the nanopore. This behavior was attributed to the nanoconfinement-induced structural reorganization of the polyelectrolyte layers, leading to the efficient formation of ion pairs and promoting a marked decrease in the net fixed charges on the nanopore walls. We consider that these results are of paramount relevance for the modification of nanopores, nanopipets, and nanoelectrodes using charged supramolecular assemblies, as well as of importance in "soft nanotechnology" provided that structural complexity, induced by nanoconfinement, can define the functional properties of self-assembled polymeric nanostructures.
基于单锥形纳米孔的离子电流整流器的分子设计正受到科学界越来越多的关注。这个主题之所以吸引人，部分原因在于人们对基于离子和分子通过纳米孔结构传输的传感器和流体纳米执行器的兴趣，而这些纳米孔结构很容易集成到功能系统中。孔壁的化学修饰不仅控制这些纳米结构的直径，还控制它们的选择性和传输特性。为了赋予固态纳米孔选择性，有必要开发和探索对孔壁进行功能化的新方法。因此，创建能够作为选择性离子通道或智能纳米流控传感器的功能性纳米孔，在很大程度上取决于我们以可预测的方式在与构建块本身尺寸相当的受限几何形状内组装和构建分子结构的能力。在这种情况下，聚电解质的层层沉积为创建具有多种功能特性的纳米尺度超分子组装体提供了一种简单的方法。在这项工作中，我们首次将层层聚电解质组装体集成到单锥形纳米孔中，以研究和探索在纳米流控装置的受限几何形状内创建带电超分子组装体所产生的功能特性。为了解决这个具有挑战性的问题，我们使用了结合实验和理论的方法来阐明和量化纳米孔内发生的静电变化在超分子组装过程中。多层膜是通过连续的层层吸附聚(烯丙基胺盐酸盐)（PAH）和聚(苯乙烯磺酸盐)（PSS）在孔表面上构建的。我们的结果表明，用 PAH/PSS 组装体功能化的单锥形纳米孔的电荷传输性质高度依赖于组装在孔壁上的层的数量。与在平面表面上沉积的 PAH/PSS 膜（定量电荷反转）不同，孔壁的表面电荷随着组装到纳米孔中的 PAH/PSS 层的数量急剧减少。这种行为归因于聚电解质层的纳米约束诱导结构重排，导致离子对的有效形成，并显著降低纳米孔壁上的固定净电荷。我们认为，这些结果对于使用带电超分子组装体修饰纳米孔、纳米管和纳米电极至关重要，并且对于“软纳米技术”也很重要，因为纳米约束引起的结构复杂性可以定义自组装聚合物纳米结构的功能特性。
