The staining technique most likely used to demonstrate amyloid in tissue is which dye?

• A. Congo red
• B. PAS
• C. Hematoxylin
• D. Alcian blue

Answer: (A)

Staining with Congo red targets amyloid because its beta-pleated sheet structure binds the dye. When tissue sections stained with Congo red are examined under polarized light, amyloid deposits produce a characteristic apple-green birefringence, which is diagnostic for amyloid. This specific optical property helps distinguish amyloid from other tissue components. Other stains—like PAS, hematoxylin, or Alcian blue—highlight carbohydrates, nuclei, or acidic mucopolysaccharides, respectively, but do not specifically reveal amyloid with the same diagnostic clarity.