Advanced Histological Techniques
Tissue Processing for Electron Microscopy
Sections for TEM must be less than 80 nm thick in order to allow at least 50% of the electron beam to penetrate the sample. This can only be accomplished by using resins for embedding (epoxy, acrylic or polyester) which requires a modification of the processing protocol. Graded alcohol baths (typically 20, 40, 70, 90 and 100%) are used for the dehydration, but in place of the clearing agents used in light microscopy, a "transitional fluid" is used. This fluid is miscible with both ethanol and the embedding resin, and is almost universally 1,2 epoxypropane (propylene oxide). If water soluble embedding resins are used, the sample may be dehydrated in graded baths of the embedding resin instead of alcohol, and a transitional fluid is not needed.
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