Price Andrew D, Schwartz Daniel K
University of Colorado, Department of Chemical and Biological Engineering, Boulder, Colorado 80309-0424, USA.
J Am Chem Soc. 2008 Jul 2;130(26):8188-94. doi: 10.1021/ja0774055. Epub 2008 Jun 4.
Interactions between DNA and an adsorbed cationic surfactant at the nematic liquid crystal (LC)/aqueous interface were investigated using polarized and fluorescence microscopy. The adsorption of octadecyltrimethylammonium bromide (OTAB) surfactant to the LC/aqueous interface resulted in homeotropic (untilted) LC alignment. Subsequent adsorption of single-stranded DNA (ssDNA) to the surfactant-laden interface modified the interfacial structure, resulting in a reorientation of the LC from homeotropic alignment to an intermediate tilt angle. Exposure of the ssDNA/OTAB interfacial complex to its ssDNA complement induced a second change in the interfacial structure characterized by the nucleation, growth, and coalescence of lateral regions that induced homeotropic LC alignment. Fluorescence microscopy showed explicitly that the complement was colocalized in the same regions as the homeotropic domains. Exposure to noncomplementary ssDNA caused no such response, suggesting that the homeotropic regions were due to DNA hybridization. This hybridization occurred in the vicinity of the interface despite the fact that the conditions in bulk solution were such that hybridization did not occur (high stringency), suggesting that the presence of the cationic surfactant neutralized electrostatic repulsion and allowed for hydrogen bonding between DNA complements. This system has potential for label-less and portable DNA detection. Indeed, LC response to ssDNA target was detected with a lower limit of approximately 50 fmol of complement and was sufficiently selective to differentiate a one-base-pair mismatch in a 16-mer target.
利用偏振显微镜和荧光显微镜研究了向列型液晶（LC）/水界面处DNA与吸附的阳离子表面活性剂之间的相互作用。十八烷基三甲基溴化铵（OTAB）表面活性剂吸附到LC/水界面导致垂直（不倾斜）的LC排列。随后单链DNA（ssDNA）吸附到负载表面活性剂的界面上改变了界面结构，导致LC从垂直排列重新定向到中间倾斜角。将ssDNA/OTAB界面复合物暴露于其ssDNA互补链会引起界面结构的第二次变化，其特征是诱导垂直LC排列的横向区域的成核、生长和聚结。荧光显微镜清楚地显示互补链与垂直畴位于相同区域。暴露于非互补ssDNA不会引起这种反应，这表明垂直区域是由于DNA杂交所致。尽管本体溶液中的条件使得杂交不会发生（高严谨性），但这种杂交仍在界面附近发生，这表明阳离子表面活性剂的存在中和了静电排斥并允许DNA互补链之间形成氢键。该系统具有用于无标记和便携式DNA检测的潜力。实际上，检测到LC对ssDNA靶标的响应，互补链的下限约为50飞摩尔，并且具有足够的选择性以区分16聚体靶标中的一个碱基对错配。
