When used as a primary fixative for electron microscopy, glutaraldehyde requires that specimens be removed after how long?

• A. 2-4 hours.
• B. 24 hours.
• C. 1 week.
• D. Immediately.

Answer: (A)

Glutaraldehyde fixes by cross-linking proteins to stabilize cellular ultrastructure for electron microscopy, and it penetrates tissues slowly. Because of this, the fixation time is kept to a few hours to ensure the fixative has enough time to penetrate the specimen and establish strong cross-links without causing excessive hardening. Removing the specimen after about two to four hours allows adequate fixation to occur and then enables the next steps—post-fixation with osmium tetroxide, dehydration, and embedding. If left in fixative longer, such as 24 hours or a week, over-fixation can occur, which can rigidify tissue and obscure fine ultrastructural details. Fixing immediately would leave the tissue under-fixed and poorly preserved.