Fluorescence of the natural dye saffron: selective reaction with eosinophil leucocyte granules.

Treatment of methanol-fixed chicken, rat, horse and human blood smears with saturated solutions of saffron in borate buffer at pH 10 results in a bright yellow-green fluorescence reaction of the acidophilic cytoplasm granules in mammalian eosinophils and chicken heterophils under violet-blue exciting light. Spectral characteristics of saffron (emission peak at 543 nm under 436 nm excitation) and its selective fluorescence with acidophilic structures support the possibility of employing this old microscopic stain as a new fluorochrome.