来自中国科学院生态环境研究中心环境化学与生态毒理学国家重点实验室的研究人员汪海林等人利用先进的单分子成像技术研究并揭示了独特的等速电泳聚焦和分离的机理，近期在《Journal of the American Chemical Society》上发表了题为“DNA单分子不连续运动成像揭示场强变化的等速电泳动力学”的研究工作（J.Am. Chem. Soc., 2013, 135 (12): 4644–4647）。

图片来源：J. Am. Chem.Soc., 2013, 135 (12): 4644–4647

带电组分在均一和非均一电场中的运动是电泳应用于化学、物理学、生命科学以及新兴的纳米科技领域的基础。目前，人们对带电组分在均一电场中的运动已经有了充分的认识，而对其在非均一电场中运动的了解却有限。认识非均一电场中带电组分的运动机制对发展高灵敏的生物分子分析技术和方法具有特殊意义。

研究人员以毛细管等速电泳作为非均一电场模型，对流经毛细管检测窗口处单个DNA分子实时成像。DNA运动速度的大小直接与电场强度相关，因此可以通过计算每一时间点DNA单分子的运动速度获得毛细管中电场强度的动态分布信息。

这项研究工作通过研究电场强度的实时变化，揭示了电渗流存在下等速电泳的动力学，并首次提出了三区带模型，突破了传统二区带模型的局限。基于这一研究成果，他们发展出一种新颖的DNA单分子聚焦方法，实现对极低浓度下随机分布的、难以检测的单分子成像，可检测出4×10^-17mol/L 的DNA分子。这项研究工作对发展基于电泳分离的高灵敏生物分析技术和方法具有重要意义。

文章链接：http://dx.doi.org/10.1021/ja400126b

英文摘要原文：

Imaging of NonuniformMotion of Single DNA Molecules Reveals the Kinetics of Varying-FieldIsotachophoresis

The nonuniform motion of charged species in a varying electric fieldmay provide unique separation and focusing power for chemical, biochemical, andnanoscale studies. We imaged in real time the nonuniform motion of single DNAmolecules under varying-field isotachophoresis (ITP) conditions. From the trajectoriesof single molecules, we obtained the time- and position-dependent electricfield strength (E) and revealed the behavior of adaption barriers withinelectro-osmotic flow (EOF)-driven and EOF-independent ITP. We found that theinitial terminating electrolyte zone of constant E is split into twozones: a highly adapted high-E zone and a low-E zone of graduallyadapting electric field. The formation of the two unique zones is associatedwith the rate-limiting mass transfer barrier in EOF-driven ITP. As a result ofthe unique E distribution, DNA molecules first slow to a stop andthen rapidly move backward to the leading electrolyte/terminating electrolyteboundary. This provides a novel mechanism for selective focusing of targetmolecules in dilute solutions of large volume. We show that the ITP focusingcan improve the detection of single DNA molecules (limit of detection = 4 × 10^-17 mol/L),which are stochastically distributed at extremely low concentrations. The ITPstrategy focuses individual molecules into a small volume that is matched withthe focal point of single-molecule imaging.

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