Which dye is commonly used as an example of a dye absorption technique for lipids?

• A. Oil Red O
• B. Hematoxylin
• C. Eosin
• D. Methylene blue

Answer: (A)

Detecting lipids uses dyes that are soluble in fats, so they solubilize and color the lipid droplets directly. Oil Red O is a fat-soluble, lipophilic dye that dissolves into neutral lipids and stains them bright red, making lipid droplets easy to see in tissue sections. Because routine paraffin processing removes lipids, lipid staining is typically done on frozen sections (or with special processing) to preserve the lipids. Oil Red O is usually paired with a counterstain like hematoxylin to provide contrast, so you get red lipid droplets against blue nuclei. The other dyes are general histological stains: hematoxylin stains nuclei blue, eosin stains cytoplasm pink, and methylene blue is a basic dye not specific for lipids, so they don’t selectively highlight lipid content.