“STEM: a re-emerging modality for cryo-imaging and tomography”
Michael Elbaum, Department of Materials and Interfaces,
Weismann Institute of Science
Until recently, cryo-electron microscopy has been nearly synonymous with wide-field TEM using phase contrast. The interferometric image formation mechanism provides high contrast but also imposes stringent conditions for reliable interpretation. Point-scanning TEM, or STEM, offers an alternative modality with several important advantages. Specifically for tomography, inelastic scattering does not interfere with image formation so losses to the energy filter are avoided. Moreover, pixel values in the image relate quantitatively to elemental composition and density, while flexible configuration of the detectors can give relative weight to light or heavy elements. We take advantage of this sensitivity to examine polyphosphate bodies in bacteria, calcium-rich granules in mitochondria, and isolated metal atoms in ferritin. These examples demonstrate how STEM can expand the range of studies addressed by cryo-microscopy and tomography.