In silver staining, which factor is used as the post-fixative to enhance membrane contrast in electron microscopy?

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Multiple Choice

In silver staining, which factor is used as the post-fixative to enhance membrane contrast in electron microscopy?

Osmium tetroxide is used as the post-fixative because it specifically targets lipids in membranes, making them electron-dense and highly visible in electron microscopy. It reacts with the unsaturated bonds in membrane phospholipids, depositing osmium and thereby darkening membranes, which enhances contrast and preserves membrane architecture during processing. Glutaraldehyde fixes proteins well but doesn’t enhance lipid membrane contrast, so it doesn’t provide the same membrane visibility. Methanol is mainly a dehydration or penetration solvent in EM prep, not a membrane-staining post-fixative. Formalin is a milder fixative more typical for light microscopy and does not boost membrane contrast in EM.

Osmium tetroxide is used as the post-fixative because it specifically targets lipids in membranes, making them electron-dense and highly visible in electron microscopy. It reacts with the unsaturated bonds in membrane phospholipids, depositing osmium and thereby darkening membranes, which enhances contrast and preserves membrane architecture during processing.

Glutaraldehyde fixes proteins well but doesn’t enhance lipid membrane contrast, so it doesn’t provide the same membrane visibility. Methanol is mainly a dehydration or penetration solvent in EM prep, not a membrane-staining post-fixative. Formalin is a milder fixative more typical for light microscopy and does not boost membrane contrast in EM.

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