Cheng Chao-Min, Kim Yongtae, Yang Jui-Ming, Leuba Sanford H, Leduc Philip R
Departments of Mechanical and Biomedical Engineering and Biological Sciences, Carnegie Mellon University, Scaife Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
Lab Chip. 2009 Aug 21;9(16):2339-47. doi: 10.1039/b907860f. Epub 2009 Jun 3.
Polymer dynamics play an important role in a diversity of fields including materials science, physics, biology and medicine. The spatiotemporal responses of individual molecules such as biopolymers have been critical to the development of new materials, the expanded understanding of cell structures including cytoskeletal dynamics, and DNA replication. The ability to probe single molecule dynamics however is often limited by the availability of small-scale technologies that can manipulate these systems to uncover highly intricate behaviors. Advances in micro- and nano-scale technologies have simultaneously provided us with valuable tools that can interface with these systems including methods such as microfluidics. Here, we report on the creation of micro-curvilinear flow through a small-scale fluidic approach, which we have been used to impose a flow-based high radial acceleration ( approximately 10(3) g) on individual flexible polymers. We were able to employ this microfluidic-based approach to adjust and control flow velocity and acceleration to observe real-time dynamics of fluorescently labeled lambda-phage DNA molecules in our device. This allowed us to impose mechanical stimulation including stretching and bending on single molecules in localized regimes through a simple and straightforward technology-based method. We found that the flexible DNA molecules exhibited multimodal responses including distinct conformations and controllable curvatures; these characteristics were directly related to both the elongation and bending dynamics dictated by their locations within the curvilinear flow. We analyzed the dynamics of these individual molecules to determine their elongation strain rates and curvatures ( approximately 0.09 microm(-1)) at different locations in this system to probe the individual polymer structural response. These results demonstrate our ability to create high radial acceleration flow and observe real-time dynamic responses applied directly to individual DNA molecules. This approach may also be useful for studying other biologically based polymers including additional nucleic acids, actin filaments, and microtubules and provide a platform to understand the material properties of flexible polymers at a small scale.
聚合物动力学在包括材料科学、物理学、生物学和医学在内的众多领域中发挥着重要作用。生物聚合物等单个分子的时空响应对于新材料的开发、对细胞结构（包括细胞骨架动力学）的深入理解以及DNA复制至关重要。然而，探测单分子动力学的能力往往受到小规模技术可用性的限制，这些技术能够操纵这些系统以揭示高度复杂的行为。微米和纳米尺度技术的进步同时为我们提供了与这些系统相互作用的宝贵工具，包括微流控等方法。在此，我们报告了通过一种小规模流体方法创建微曲线流的过程，我们已使用该方法对单个柔性聚合物施加基于流的高径向加速度（约10³g）。我们能够采用这种基于微流控的方法来调节和控制流速和加速度，以观察我们装置中荧光标记的λ噬菌体DNA分子的实时动力学。这使我们能够通过一种基于简单直接技术的方法，在局部区域对单个分子施加包括拉伸和弯曲在内的机械刺激。我们发现柔性DNA分子表现出多模态响应，包括不同的构象和可控的曲率；这些特性直接与由它们在曲线流中的位置所决定的伸长和弯曲动力学相关。我们分析了这些单个分子的动力学，以确定它们在该系统中不同位置的伸长应变率和曲率（约0.09μm⁻¹），以探测单个聚合物的结构响应。这些结果证明了我们创建高径向加速度流并观察直接应用于单个DNA分子的实时动态响应的能力。这种方法也可能有助于研究其他基于生物的聚合物，包括其他核酸、肌动蛋白丝和微管，并提供一个平台来在小尺度上理解柔性聚合物的材料特性。
