Which reagents are used in the Prussian Blue reaction?

• A. 2% Potassium Ferrocyanide and 2% Hydrochloric Acid
• B. Silver nitrate and ammonia
• C. Eosin and hematoxylin
• D. Methylene blue and Azure A

Answer: (A)

Prussian Blue staining detects ferric iron (Fe3+) in tissue by forming an insoluble blue compound when iron is exposed to ferrocyanide in acidic conditions. The acid helps release iron from storage forms in the tissue, and the ferrocyanide provides the ferrocyanide ion that combines with Fe3+ to produce ferric ferrocyanide, the characteristic blue pigment. The combination of potassium ferrocyanide with hydrochloric acid is the classic and effective pair used to generate this blue product in the Perls’ stain. That’s why this option is correct: it supplies both the ferrocyanide reagent and the acid necessary for the reaction.

The other options involve different staining chemistries. Silver nitrate with ammonia is used for silver staining methods, not for Prussian Blue. Eosin and hematoxylin are the components of standard H&E staining for general tissue morphology. Methylene blue and Azure A are dyes used for other metachromatic or basic dye stains. None of these yield the characteristic Prussian Blue color reaction for ferric iron.