Question

Which stain is used for electron microscopy?

• A. PAS
• B. Aurantia
• C. Para Rosailin
• D. Osmium tetraoxide

Answer 1

The correct option is D Osmium tetraoxide

Osmium tetraoxide OsO${}_4$ is a widely used staining agent used in transmission electron microscopy (TEM) to provide contrast to the image. As a lipid stain, it is also useful in scanning electron microscopy (SEM) as an alternative to sputter coating. It embeds a heavy metal directly into cell membranes, creating a high electron scattering rate without the need for coating the membrane with a layer of metal, which can obscure details of the cell membrane. In the staining of the plasma membrane, osmium (VIII) oxide binds phospholipid head regions, thus, creating contrast with the neighbouring protoplasm (cytoplasm). Additionally, osmium (VIII) oxide is also used for fixing biological samples in conjunction with HgCl${}_2$. Its rapid killing abilities are used to quickly kill live specimens such as protozoa. OsO${}_4$ stabilizes many proteins by transforming them into gels without destroying structural features.