Which statement about glutaraldehyde is true?

• A. It penetrates slowly and is best for electron microscopy due to ultrastructure preservation
• B. It penetrates quickly and is used for rapid processing
• C. It is a noncoagulant fixative
• D. It is used at high concentrations (50%)

Answer: (A)

Glutaraldehyde is prized in electron microscopy because it cross-links proteins very effectively, locking cellular structures in place so ultrastructural details—membranes, organelles, and fine filaments—are exquisitely preserved. Its molecules are relatively large, so they diffuse into tissue slowly. That slow penetration is why it’s not used for rapid processing, but once it fixes, the resulting preservation of fine detail is exceptional for EM. In practice, tissues are fixed in a moderate concentration (around 2–4%) in buffer, sometimes followed by postfixation with osmium tetroxide to enhance membrane contrast. The statement about slow penetration and ultrastructure preservation is thus the correct one, while rapid processing or unusually high concentrations (like 50%) do not describe typical glutaraldehyde use.