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Topographic Imaging of Chromium-Coated Frozen-Hydrated Cell and Macromolecular Complexes by In-Lens Field Emission Scanning Electron Microscopy

Published online by Cambridge University Press:  31 July 2002

Robert P. Apkarian
Affiliation:
Department of Chemistry, Emory University, Atlanta
Kevin L. Caran
Affiliation:
Department of Chemistry, Emory University, Atlanta
Keith A. Robinson
Affiliation:
Department of Medicine, Division of Cardiology, Emory University, Atlanta
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Abstract

An in-lens Schottky field emission scanning electron microscope (SEM) combined with a transmission electron microscope (TEM)-type cold-stage and a chromium (Cr) sputter-coating system was developed to rapidly prepare and cryo-image biological specimens to attain accurate nanometer-level structural information. High-resolution topographic images at high primary magnification ([eg ]200,000 times) were digitally recorded with very short dwell times and without beam damage. Plunge freezing in ethane, followed by fracturing, Cr coating, and in-lens cryo-high-resolution scanning electron microscope (HRSEM) imaging directly revealed macromolecular features of yeast cells, platelets, and cell-free elastin analogues. The 'vitreous' nature of bulk water in its solid state appeared featureless in cryo-HRSEM images, suggesting that if ice crystals were present they would be [el ]2–3 nm (the approximate instrument resolution on cryo-specimens). Compared to technically difficult and indirect freeze-fracture TEM replicas, cryo-HRSEM samples are fully hydrated, unfixed, noncryoprotected specimens immersed in featureless ice. The time necessary to cryo-immobilize the specimen and record the image is <3 hr. The hexagonal arrays of intramembrane particles on the protoplasmic face of yeast cells and differences in surface morphology between thrombin-stimulated and quiescent platelets were assessed. A clear interface line between collapsed elastin fibril lacework and vitreous lakes was commonly observed. These experiments demonstrate the feasibility of this technique to rapidly evaluate macromolecular features in cryofixed cells and cell-free systems.

Type
Articles
Copyright
© 1999 Microscopy Society of America

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