Center for Cellular Imaging and Nanoanalytics, Biozentrum, University Basel, CH-4058 Basel, Switzerland.
Micron. 2011 Feb;42(2):186-95. doi: 10.1016/j.micron.2010.10.002. Epub 2010 Oct 13.
The scanning transmission electron microscope (STEM) and the atomic force microscope (AFM) have provided a wealth of useful information on a wide variety of biological structures. These instruments have in common that they raster-scan a probe over a sample and are able to address single molecules. In the STEM the probe is a focused electron beam that is deflected by the scan-coils. Detectors collecting the scattered electrons provide quantitative information for each sub-nanometer sized sample volume irradiated. These electron scattering data can be reconstituted to images of single macromolecules or can be integrated to provide the mass of the macromolecules. Samples need to be dehydrated for such quantitative STEM imaging. In contrast, the AFM raster-scans a sharp tip over a sample surface submerged in a buffer solution to acquire information on the sample's surface topography at sub-nanometer resolution. Direct observation of function-related structural changes induced by variation of temperature, pH, ionic strength, and applied force provides insight into the structure-function relationship of macromolecules. Further, the AFM allows single molecules to be addressed and quantitatively unfolded using the tip as nano-tweezers. The performance of these two scanning probe approaches is illustrated by several examples including the chaperonin GroEL, bacterial surface layers, protein crystals, and bacterial appendices.
扫描透射电子显微镜（STEM）和原子力显微镜（AFM）为各种生物结构提供了丰富的有用信息。这两种仪器的共同点是它们通过扫描线圈对探针进行光栅扫描，并能够对单个分子进行寻址。在 STEM 中，探针是聚焦的电子束，它被扫描线圈偏转。收集散射电子的探测器为每个亚纳米大小的辐照样品体积提供定量信息。这些电子散射数据可以重建为单个大分子的图像，也可以进行积分以提供大分子的质量。这种定量 STEM 成像需要对样品进行脱水处理。相比之下，AFM 通过在缓冲溶液中浸没的样品表面上扫描一个尖锐的尖端，以亚纳米分辨率获取样品表面形貌的信息。通过温度、pH 值、离子强度和施加力的变化直接观察功能相关的结构变化，为大分子的结构-功能关系提供了深入的了解。此外，AFM 允许使用尖端作为纳米镊子来寻址和定量展开单个分子。这两种扫描探针方法的性能通过几个例子来说明，包括分子伴侣 GroEL、细菌表面层、蛋白质晶体和细菌附属物。
