Osmium tetroxide is primarily used to fix which tissue component?

• A. Lipids
• B. Proteins
• C. Nucleic acids
• D. Carbohydrates

Answer: (A)

Osmium tetroxide’s defining role is fixing lipids. It reacts with the carbon–carbon double bonds in unsaturated fatty acids, forming osmiated lipids that become stabilized and highly electron-dense. This preserves lipid-rich structures such as membranes and provides the contrast needed for electron microscopy. In contrast, proteins are primarily fixed by aldehydes that cross-link amino groups, nucleic acids are not the main target of OsO4, and carbohydrates aren’t the primary component osmium tetroxide fixes. So the tissue component best fixed by osmium tetroxide is lipids.