Zamboni solution allows secondary fixation with which agent?

• A. Osmium tetroxide
• B. Glutaraldehyde
• C. Formalin
• D. Methanol

Answer: (A)

Zamboni solution is used to fix tissue in a way that preserves membranes and lipids, setting the stage for a second fixation that enhances lipid contrast for electron microscopy. Osmium tetroxide is the best choice for this secondary fixation because it specifically reacts with unsaturated lipids, forming electron-dense complexes that dramatically improve membrane visualization in TEM. The Zamboni fixative maintains lipid accessibility and tissue structure so OsO4 can effectively fix and stain those lipids. Other options don’t provide the same lipid-focused postfixation: formalin and glutaraldehyde mainly fix proteins and aren’t chosen for enhancing lipid contrast, while methanol can dehydrate and extract lipids, reducing OsO4 effectiveness.