Which fixative is described as the primary fixative for electron microscopy?

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Preserving ultrastructure for electron microscopy relies on strong cross-linking of proteins to lock cellular components in place. Glutaraldehyde is the preferred primary fixative because it is a bifunctional aldehyde that forms extensive cross-links between amino groups in proteins, stabilizing fine intracellular architecture and membranes so it remains intact during subsequent processing and heavy-metal staining. After this primary fixation, osmium tetroxide is commonly used as a secondary fixative to fix lipids and enhance membrane contrast by increasing electron density. Formalin is more suited to light microscopy and does not preserve ultrastructural detail as well, while picric acid appears in other fixative formulations and isn’t the standard primary fixative for EM. So, glutaraldehyde best fits the role of primary fixative for electron microscopy.