Electron microscope

The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times.

Treatment

Samples viewed under an electron microscope may be treated in many ways:

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• Cryofixation - freezing a specimen so rapidly, to liquid nitrogen temperatures, that the water forms vitreous (non-crystalline) ice. This preserves the specimen in a snapshot of its solution state. This technique produces the best specimen preservation, but isn't applicable to all specimens.
• Fixation - preserving the sample to make it more realistic. Glutaraldehyde - for hardening - and osmic acid - which stains lipids black - are used.
• Dehydration - the removing of water to be replaced with an embedding medium such as ethanol or propanone.
• Embedding - supports the tissue for sectioning in a resin such as araldite.
• Sectioning - produces thin slices for mounting. These can be cut on an ultramicrotome with a diamond knife to produce very thin slices. Glass knives are also used because they can be made in the lab and are much cheaper.
• Staining - uses metals such as lead and uranium to block electrons to give contrast between different structures, since many (especially biological) materials are nearly transparent to electrons.
• Ion Beam Milling - thins samples until they are transparent to electrons by firing ions (typically argon) at the surface from an angle and sputtering material from the surface. A subclass of this is Focussed Ion Beam milling, where gallium ions are used to produce an electron transparent membrane in a specific region of the sample, for example through a device within a microprocessor.