Which fixative is preferred for preserving fine cellular detail for electron microscopy?

• A. Glutaraldehyde
• B. Formalin
• C. Bouin
• D. Alcohol

Answer: (A)

For electron microscopy, the goal is to lock cellular structures in place with very stable, specific cross-linking, so the fine ultrastructure—especially membranes and organelles—remains intact and recognizable. Glutaraldehyde does exactly that by forming covalent cross-links between protein molecules, rapidly and robustly fixing tissue at the microscopic level. This preserves the architecture of membranes, cytoskeletal elements, and organelles in exquisite detail, which is essential for the high-resolution images EM provides.

Formalin (formaldehyde) penetrates tissue well and is excellent for light microscopy, but it forms fewer cross-links and yields less stable ultrastructure, so fine details don’t hold up as well under the processing and high magnification of EM. Bouin’s solution, while good for general morphology, contains picric acid and can introduce artifacts or interfere with subsequent staining, making it suboptimal for ultrastructural work. Alcohol fixes precipitate proteins and tend to extract lipids, leading to poor preservation of membranes and overall ultrastructure.

In practice, tissue fixed with glutaraldehyde is often followed by osmium tetroxide fixation to stabilize and stain membranes further, providing the best contrast and preservation for electron microscopy.