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
Famous quotes containing the word development:
“I’ve always been impressed by the different paths babies take in their physical development on the way to walking. It’s rare to see a behavior that starts out with such wide natural variation, yet becomes so uniform after only a few months.”
—Lawrence Kutner (20th century)
“This was the Eastham famous of late years for its camp- meetings, held in a grove near by, to which thousands flock from all parts of the Bay. We conjectured that the reason for the perhaps unusual, if not unhealthful development of the religious sentiment here, was the fact that a large portion of the population are women whose husbands and sons are either abroad on the sea, or else drowned, and there is nobody but they and the ministers left behind.”
—Henry David Thoreau (1817–1862)
“There are two things which cannot be attacked in front: ignorance and narrow-mindedness. They can only be shaken by the simple development of the contrary qualities. They will not bear discussion.”
—John Emerich Edward Dalberg, 1st Baron Acton (1834–1902)