What does Alizarin Red S calcium stain detect in tissue?

• A. Calcium in tissue
• B. Proteins in tissue
• C. Lipids in tissue
• D. Nucleic acids in tissue

Answer: (A)

Alizarin Red S is a calcium stain. It binds selectively to calcium salts found in mineralized tissue and calcified deposits, producing a bright red to orange-red color where calcium accumulates. This makes it useful for identifying bone mineralization and pathological calcifications. It does not bind to proteins, lipids, or nucleic acids, which is why those components don’t stain with this dye. In short, the stain highlights calcium in tissue.