Development
The original rationale for cryoelectron microscopy was as a means to fight radiation damage for biological specimens. The amount of radiation required to collect an image of a specimen in the electron microscope is comparable to placing the sample about 20 m away from a thermonuclear device. In addition, the high vacuum required on the column of an electron microscope makes the environment for the sample quite harsh.
The problem of the vacuum was partially solved by the introduction of negative stains such as uranium salts (uranyl acetate is perhaps the most common negative stain), but even with negative stains, biological samples are prone to structural collapse upon dehydration of the specimen. Embedding the samples in ice below the sublimation temperature was a possibility that was contemplated early on, but water tends to arrange into a crystalline lattice of lower density upon freezing and this tends to destroy the structure of anything that is embedded in it.
In the early 80's, several groups studying solid state physics were attempting to produce vitreous ice by different means, such as high pressure freezing or flash freezing. Theoretical calculations deemed this task impossible, but in a seminal paper in 1984, the group led by Jacques Dubochet at the European Molecular Biology Laboratory showed images of adenovirus embedded in a vitrified layer of water. This paper is generally considered to mark the birth of cryoelectron microscopy, and the technique has been developed to the point of becoming routine at several laboratories throughout the world.
Read more about this topic: Cryo-electron Microscopy
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