Semiconductor and Dimensional Metrology Division, Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA.
Lab Chip. 2012 Mar 21;12(6):1174-82. doi: 10.1039/c2lc21152a. Epub 2012 Jan 26.
A complex entropy gradient for confined DNA molecules was engineered for the first time. Following the second law of thermodynamics, this enabled the directed self-transport and self-concentration of DNA molecules. This new nanofluidic method is termed entropophoresis. As implemented in experiments, long DNA molecules were dyed with cyanine dimers, dispersed in a high ionic strength buffer, and confined by a nanofluidic channel with a depth profile approximated by a staircase function. The staircase step depths spanned the transition from strong to moderate confinement. The diffusion of DNA molecules across slitlike steps was ratcheted by entropic forces applied at step edges, so that DNA molecules descended and collected at the bottom of the staircase, as observed by fluorescence microscopy. Different DNA morphologies, lengths, and stoichiometric base pair to dye molecule ratios were tested and determined to influence the rate of transport by entropophoresis. A model of ratcheted diffusion was used to interpret a shifting balance of forces applied to linear DNA molecules of standard length in a complex free energy landscape. Related metrics for the overall and optimum performance of entropophoresis were developed. The device and method reported here transcend current limitations in nanofluidics and present new possibilities in polymer physics, biophysics, separation science, and lab-on-a-chip technology.
首次设计出一种用于受限 DNA 分子的复杂熵梯度。根据热力学第二定律，这使得 DNA 分子能够定向自我传输和自我浓缩。这种新的纳流控方法称为熵推进。在实验中，长 DNA 分子用花青二聚体染色，分散在高离子强度缓冲液中，并通过深度轮廓近似为阶梯函数的纳流控通道限制。阶梯的步深跨越了从强约束到中等约束的转变。DNA 分子在狭缝状台阶上的扩散是由在台阶边缘施加的熵力驱动的，因此 DNA 分子下降并收集在阶梯的底部，如荧光显微镜观察到的那样。通过实验测试并确定了不同的 DNA 形态、长度和碱基对与染料分子的化学计量比，以影响熵推进的传输速率。使用棘轮扩散模型来解释标准长度线性 DNA 分子在复杂自由能景观中所施加的力的平衡转移。开发了用于熵推进的整体和最佳性能的相关度量标准。这里报道的设备和方法超越了纳流控的当前限制，并在聚合物物理、生物物理、分离科学和片上实验室技术方面带来了新的可能性。
