Cryo EM
The major development of the 1980s was the invention of cryo EM. This largely solved 2 major problems that had held up the field: damage to the specimen by electron irradiation and by the dehydration necessary for stability in the high vacuum environment inside the microscope. An EM grid with a thin layer of solution containing the macromolecular structure is trapped in a solid, glass-like state vitrified water by plunging into liquid ethane. The grid is transferred and maintained in the microscope with liquid nitrogen cooling. The low temperature stabilizes the vitrified sample in the vacuum, and moreover slows down the rate of electron beam damage. Thus, the native hydrated structure is observed directly, although with extremely low contrast and signal:noise. |
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