Which dye is a copper phthalocyanin basic dye that is water soluble and appears blue because of copper?

• A. Alcian blue
• B. Eosin
• C. Hematoxylin
• D. Methylene blue

Answer: (A)

Alcian blue is a copper phthalocyanine basic dye that is water soluble, and its blue color comes from the copper center in the phthalocyanine ring. The sulfonate groups make it water soluble, allowing it to bind to negatively charged acidic mucopolysaccharides in tissue. As a basic dye, it carries positive charges that interact with these acidic substances, producing the characteristic blue stain. The other dyes listed are not copper phthalocyanine dyes: eosin is an acidic dye that stains pink, hematoxylin stains nuclei via a different complex, and methylene blue is a different basic dye not based on copper phthalocyanine.