What is the fixative used for electron microscopy?

• A. Zambini and osmium tetroxide
• B. Bouin Solution
• C. Formalin
• D. Glutaraldehyde

Answer: (A)

Electron microscopy relies on fixation that preserves ultrastructure, especially membranes, and provides strong electron contrast. Osmium tetroxide is the key postfix fixative for EM because it fixes lipids in membranes and greatly enhances membrane visibility by adding electron density. Pairing a robust primary fixative like Zamboni’s fixative with osmium tetroxide ensures both proteins and membranes are well preserved and contrasted, giving sharp, reliable ultrastructural details for imaging. In contrast, Bouin’s solution and formalin are more suited to light microscopy and tend to distort or fail to preserve membranes adequately for EM, and while glutaraldehyde is a common primary fixative, the standard EM approach highlighted here centers on osmium tetroxide’s critical role in membrane preservation and contrast.