Acidic and neutral lipids can be distinguished by which reagent?

• A. Nile blue sulfate
• B. Alcian blue
• C. Oil Red O
• D. Sudan Black B

Answer: (A)

Distinguishing acidic from neutral lipids relies on a stain that binds selectively to one lipid class. Nile blue sulfate is the reagent that does this differential staining: it binds to acidic lipids (such as phospholipids and glycolipids) and stains them blue, while neutral lipids are not stained by this dye in the same way, allowing you to tell the two classes apart within the same tissue section. This specific differentiation isn’t offered by the other reagents listed. Alcian blue is for acidic mucopolysaccharides, not lipids; Oil Red O targets neutral lipids (triglycerides) but doesn’t distinguish acid lipids; Sudan Black B stains lipids more generally without differentiating acid versus neutral.