Bustamante C, Vesenka J, Tang C L, Rees W, Guthold M, Keller R
Institute of Molecular Biology, University of Oregon, Eugene 97403.
Biochemistry. 1992 Jan 14;31(1):22-6. doi: 10.1021/bi00116a005.
Routine and reproducible imaging of DNA molecules in air with the scanning force microscope (SFM) has been accomplished. Circular molecules of plasmid DNA were deposited onto red mica and imaged under various relative humidities. In related experiments, the first images of the Escherichia coli RNA polymerase-DNA complex have also been obtained. This has been possible by (1) the use of specially modified SFM tips with a consistent radius of curvature of 10 nm or less, to minimize the amount of image distortion introduced by the finite dimensions of commercially available tips, (2) the optimization of a method to deposit and bind DNA molecules to the mica surface in a stable fashion, and (3) careful control of the sample humidity, to prevent solvation of the molecules and detachment from the surface by the scanning tip or stylus. Contact forces in the range of a few nanonewtons are routinely possible in air and in the presence of residual humidity. The spatial resolution of the images appears determined by the radius of curvature of the modified styli, which can be estimated directly from the apparent widths of the DNA molecules in the images.
利用扫描力显微镜（SFM）对空气中的DNA分子进行常规且可重复的成像已经实现。将质粒DNA的环状分子沉积在红色云母上，并在不同相对湿度下进行成像。在相关实验中，还获得了大肠杆菌RNA聚合酶 - DNA复合物的首张图像。这之所以成为可能，是因为：（1）使用了经过特殊修饰、曲率半径一致为10纳米或更小的SFM探针，以尽量减少市售探针有限尺寸所引入的图像失真量；（2）优化了一种以稳定方式将DNA分子沉积并结合到云母表面的方法；（3）仔细控制样品湿度，以防止分子溶剂化以及被扫描探针或触针从表面分离。在空气中且存在残余湿度的情况下，通常可以实现几纳牛顿范围内的接触力。图像的空间分辨率似乎由修饰后的探针曲率半径决定，这可以直接从图像中DNA分子的表观宽度估算出来。
