Scanning transmission electron microscopes (STEMs) can both measure the mass of single-protein complexes and take amazingly clear images of such complexes, offering a wide range of applications in structural biology. The scanning electron beam focused to a diameter of a few Ångstroms irradiates a roughly cylindrical volume of a thin sample. All atoms of this cylinder scatter electrons elastically and inelastically according to their scattering cross sections. Because no postspecimen optical system is required, essentially all scattered electrons can be captured and used for quantitative measurements. This chapter describes the image formation in the STEM, the principle of mass measurements, and presents a few studies achieved with the Vacuum Generators HB-5 STEM in Basel. The chapter concludes with the proposal to use STEM for single-cell proteomics. © 2009 Elsevier Inc. All rights reserved.
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