Which technique is an example of dye absorption?

• A. Oil Red O
• B. Sudan IV
• C. Alcian Blue
• D. Crystal Violet

Answer: (A)

Dye absorption refers to pigments that enter and dissolve into lipid components of the tissue, staining the lipids themselves rather than binding to specific tissue molecules. Oil Red O is a fat-soluble dye that partitions into neutral lipids, such as triglycerides in stored fat, staining these lipid droplets a vivid red. This makes it a classic example of a dye absorption technique, because the color comes from the dye dissolving into and outlining the lipid inclusions rather than attaching to fixed tissue structures. Note that this approach works best on frozen sections or tissues processed to preserve lipids, since routine processing can remove lipids. By contrast, Alcian Blue targets acidic mucopolysaccharides through ionic binding, and Crystal Violet stains by binding to cellular and structural components; Sudan IV is another lipid-soluble dye but Oil Red O is the standard example highlighted for absorption into lipids.