Nanoscience Center and Institute of Chemistry, Copenhagen University, Universitetsparken 5, DK-2100 Copenhagen E, Denmark.
Langmuir. 2011 Oct 18;27(20):12506-14. doi: 10.1021/la202087u. Epub 2011 Sep 16.
In this article, we discuss the structure and composition of mixed DNA-cationic surfactant adsorption layers on both hydrophobic and hydrophilic solid surfaces. We have focused on the effects of the bulk concentrations, the surfactant chain length, and the type of solid surface on the interfacial layer structure (the location, coverage, and conformation of the DNA and surfactant molecules). Neutron reflectometry is the technique of choice for revealing the surface layer structure by means of selective deuteration. We start by studying the interfacial complexation of DNA with dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (CTAB) on hydrophobic surfaces, where we show that DNA molecules are located on top of a self-assembled surfactant monolayer, with the thickness of the DNA layer and the surfactant-DNA ratio determined by the surface coverage of the underlying cationic layer. The surface coverages of surfactant and DNA are determined by the bulk concentration of the surfactant relative to its critical micelle concentration (cmc). The structure of the interfacial layer is not affected by the choice of cationic surfactant studied. However, to obtain similar interfacial structures, a higher concentration in relation to its cmc is required for the more soluble DTAB surfactant with a shorter alkyl chain than for CTAB. Our results suggest that the DNA molecules will spontaneously form a relatively dense, thin layer on top of a surfactant monolayer (hydrophobic surface) or a layer of admicelles (hydrophilic surface) as long as the surface concentration of surfactant is great enough to ensure a high interfacial charge density. These findings have implications for bioanalytical and nanotechnology applications, which require the deposition of DNA layers with well-controlled structure and composition.
本文讨论了混合 DNA-阳离子表面活性剂吸附层在疏水和亲水固体表面上的结构和组成。我们专注于本体浓度、表面活性剂链长和固体表面类型对界面层结构（DNA 和表面活性剂分子的位置、覆盖度和构象）的影响。通过选择性氘化，中子反射技术是揭示表面层结构的首选技术。我们首先研究了 DNA 与十二烷基三甲基溴化铵（DTAB）和十六烷基三甲基溴化铵（CTAB）在疏水表面上的界面络合作用，结果表明 DNA 分子位于自组装表面活性剂单层的顶部，DNA 层的厚度和表面活性剂-DNA 比由底层阳离子层的表面覆盖率决定。表面活性剂和 DNA 的表面覆盖率由表面活性剂相对于其临界胶束浓度 (cmc) 的本体浓度决定。所研究的阳离子表面活性剂的选择不会影响界面层的结构。然而，为了获得相似的界面结构，需要用较短烷基链的更易溶的 DTAB 表面活性剂以高于其 cmc 的浓度来取代 CTAB。我们的结果表明，只要表面活性剂的表面浓度足以确保高界面电荷密度，DNA 分子将自发地在表面活性剂单层（疏水表面）或混合胶束层（亲水表面）的顶部形成相对致密、薄的层。这些发现对需要具有良好控制结构和组成的 DNA 层沉积的生物分析和纳米技术应用具有重要意义。
