Perkins T T, Smith D E, Larson R G, Chu S
Department of Physics, Stanford University, CA 94305, USA.
Science. 1995 Apr 7;268(5207):83-7. doi: 10.1126/science.7701345.
The stretching of single, tethered DNA molecules by a flow was directly visualized with fluorescence microscopy. Molecules ranging in length (L) from 22 to 84 micrometers were held stationary against the flow by the optical trapping of a latex microsphere attached to one end. The fractional extension x/L is a universal function of eta vL 0.54 +/- 0.05, where eta and v are the viscosity and velocity of the flow, respectively. This relation shows that the DNA is not "free-draining" (that is, hydrodynamic coupling within the chain is not negligible) even near full extension (approximately 80 percent). This function has the same form over a long range as the fractional extension versus force applied at the ends of a worm-like chain. For small deformations (< 30 percent of full extension), the extension increases with velocity as x approximately v0.70 +/- 0.08. The relative size of fluctuations in extension decreases as sigma x/x approximately equal to 0.42 exp (-4.9 x/L). Video images of the fluctuating chain have a cone-like envelope and show a sharp increase in intensity at the free end.
通过荧光显微镜直接观察了单个、受束缚的DNA分子在流动中的拉伸情况。长度（L）在22至84微米之间的分子，通过附着在一端的乳胶微球的光学捕获而在流动中保持静止。分数伸长率x/L是ηvL^0.54±0.05的通用函数，其中η和v分别是流动的粘度和速度。该关系表明，即使在接近完全伸长（约80%）时，DNA也不是“自由排水”的（即链内的流体动力耦合不可忽略）。该函数在很长范围内与蠕虫状链末端施加的力与分数伸长率的关系具有相同的形式。对于小变形（<完全伸长的30%），伸长率随速度增加，x约为v^0.70±0.08。伸长率波动的相对大小随σx/x≈0.42 exp(-4.9x/L)而减小。波动链的视频图像具有类似圆锥的包络，并且在自由端强度急剧增加。
