Regulating the Translocation of DNA through Poly(N‑isopropylacrylamide)-Decorated Switchable Nanopores by Cononsolvency Effect

Stimulus response of polymer-decorated nanopores/nanochannels is a fascinating topic both in polymer science and modern nanotechnology; however, it is still challenging for standard analytical methods to characterize these switchable nanopores/nanochannels. In this study, based on the physics of polymer translocation, we developed an analytical method and thus for the first time were able to quantitatively measure the effective thickness of the polymer layer around the rim of nanopores. As an application example of this method, we studied the translocation dynamics of fluorescence DNA through poly­(N-isopropylacrylamide)-decorated switchable nanopores in aqueous environments. By adding small amounts of ethanol to the aqueous buffer solution, a switch-like response of the DNA translocation can be observed. It is also observed that a pronounced switching effect can be only realized in a window of moderate grafting densities of the poly­(N-isopropylacrylamide) layer. These are attributed to the cononsolvency effect which causes a collapse of the polymer layer and thus a transition between “closed” and “open” states of the nanopores for DNA translocation. Our study clearly transpired that the cononsolvency effect of polymers can be used as a novel trigger to change the size of nanopores, in analogy to the opening and closure of the gates of cell membrane channels. We envisage that our study will spawn further developments for the design of switchable nanogates and nanopores.

聚合物修饰纳米孔/纳米通道的刺激响应行为，是高分子科学与现代纳米技术领域极具吸引力的研究课题。然而，采用常规分析方法对这类可切换纳米孔/纳米通道进行表征仍颇具挑战。本研究基于聚合物跨孔易位的物理机制，开发了一种分析方法，首次实现了对纳米孔边缘聚合物层有效厚度的定量表征。作为该方法的应用实例，我们研究了荧光标记DNA在水相环境中，穿过聚(N-异丙基丙烯酰胺)(poly(N-isopropylacrylamide))修饰的可切换纳米孔的输运动力学过程。通过向水相缓冲液中添加少量乙醇，可观测到DNA输运出现类开关响应行为。同时研究发现，仅在聚(N-异丙基丙烯酰胺)层的接枝密度处于中等范围时，才能实现显著的开关效应。该现象可归因于共非溶剂化效应：该效应会引发聚合物层塌陷，进而使纳米孔在DNA输运时呈现"闭合"与"开放"两种状态的切换。本研究明确证实，聚合物的共非溶剂化效应可作为一种全新的调控手段，实现纳米孔孔径的动态调节，这与细胞膜通道的门控开闭过程具有相似性。我们预计本研究将为可切换纳米门与纳米孔的设计研发提供新的发展思路。