Single molecule diffusion on hard, soft and fluid surfaces
Single molecule diffusion on hard, soft and fluid surfaces
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硬、软和流体表面上的单分子扩散
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
Yingxi Zhu
中科院分区：
文献类型：
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作者：
Shengqin Wang;Benxin Jing;Yingxi Zhu
表面上的分子扩散通常被认为是表面上相邻吸附位点之间的分子跳跃的热能激活过程，并且简单地由分子-表面相互作用决定。在这项工作中，我们报告了不同的扩散动力学的探针分子在甲基封端的自组装单层（SAM），聚合物刷层和脂质双层通过使用荧光相关光谱（FCS）在单分子水平。我们已经观察到，尽管较弱的分子-表面相互作用，探针分子在软聚合物刷表面和流体脂质双层上的表面扩散可以比在硬SAM表面上慢得多，这表明底层涂层的界面动力学对分子表面扩散的强烈影响。为了进一步研究热活化分子跳跃和软表面动力学的耦合，我们研究了探针分子在不同接枝密度和厚度的聚合物刷上的扩散，其中分子-表面相互作用几乎保持不变，但表面接枝的PNIPAM链的构象和动力学变化很大;令人惊讶的是观察到探针分子的扩散在较低接枝密度或较高刷厚度的PNIPAM刷表面上可以进一步延迟，从而显示出最佳刷厚度范围的存在，以促进吸附的探针分子的快速表面扩散。所有的观察相结合，导致一个通用的模型，考虑到下面的表面层的动力学来阐明不同表面上的分子扩散机制。
Molecular diffusion on a surface is often considered as a thermal energy-activated process of molecular hopping between adjacent adsorption sites on a surface and simply determined by molecule–surface interaction. In this work, we report distinct diffusive dynamics of probe molecules on methyl-terminated self-assembled monolayer (SAM), polymer brush layer and lipid bilayer by using fluorescence correlation spectroscopy (FCS) at a single-molecule level. We have observed that despite weaker molecule–surface interaction, the surface diffusion of probe molecules on soft polymer brush surface and fluid lipid bilayer can be much slower than that on hard SAM surface, suggesting a strong impact of interfacial dynamics of the underlying coating on molecular surface diffusion. To further examine the coupling of thermal activated molecular hopping and soft surface dynamics, we have investigated the diffusion of probe molecules on polymer brushes of varied grafting density and thickness, where the molecule–surface interaction remains nearly the same, yet the adopted conformations and dynamics of surface-grafted PNIPAM chains vary considerably; it is striking to observe that the diffusion of probe molecules could be further retarded on PNIPAM brush surfaces of lower grafting density or higher brush thickness, thereby exhibiting the presence of an optimal brush thickness range to facilitate fast surface diffusion of adsorbed probe molecules. All the observations combined lead to a general model by taking the dynamics of underlying surface layers into account to elucidate the molecular diffusion mechanism on varied surfaces.