What is the primary fixative used for electron microscopy?

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Multiple Choice

What is the primary fixative used for electron microscopy?

Preserving fine cellular ultrastructure for electron microscopy requires a fixative that creates strong covalent bonds to lock proteins in place. Glutaraldehyde fits this role best because it has two reactive aldehyde groups per molecule, allowing rapid, extensive cross-linking of amino groups on proteins. This network stabilizes the delicate architecture of membranes, organelles, and cytoskeletal elements so they remain intact through the rigorous processing steps of EM preparation. Osmium tetroxide, while crucial, serves a different purpose: it is used after the initial fixation to fix lipids and to provide electron density that enhances membrane contrast. Its slower penetration and lipid-specific action mean it’s not suitable as the primary fixative. Formalin (common light-microscopy fixative) and acetone are used in other contexts—formalin is milder and better for routine light microscopy, while acetone is a dehydrating solvent used during processing, not to preserve ultrastructure as a primary fixative.

Preserving fine cellular ultrastructure for electron microscopy requires a fixative that creates strong covalent bonds to lock proteins in place. Glutaraldehyde fits this role best because it has two reactive aldehyde groups per molecule, allowing rapid, extensive cross-linking of amino groups on proteins. This network stabilizes the delicate architecture of membranes, organelles, and cytoskeletal elements so they remain intact through the rigorous processing steps of EM preparation.

Osmium tetroxide, while crucial, serves a different purpose: it is used after the initial fixation to fix lipids and to provide electron density that enhances membrane contrast. Its slower penetration and lipid-specific action mean it’s not suitable as the primary fixative.

Formalin (common light-microscopy fixative) and acetone are used in other contexts—formalin is milder and better for routine light microscopy, while acetone is a dehydrating solvent used during processing, not to preserve ultrastructure as a primary fixative.

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