Eosin

Eosin is a fluorescent red dye resulting from the action of bromine on fluorescein. It can be used to stain cytoplasm, collagen and muscle fibers for examination under the microscope. Structures that stain readily with eosin are termed eosinophilic.

Variants

There are actually two very closely related compounds commonly referred to as eosin. Most often used is eosin Y (also known as eosin Y ws, eosin yellowish, Acid Red 87, C.I. 45380, bromoeosine, bromofluoresceic acid, D&C Red No. 22); it has a very slightly yellowish cast. The other eosin compound is eosin B (eosin bluish, Acid Red 91, C.I. 45400, Saffrosine, Eosin Scarlet, or imperial red); it has a very faint bluish cast. The two dyes are interchangeable, and the use of one or the other is a matter of preference and tradition.

Eosin Y is a tetrabromo derivate of fluorescein.

Eosin B is a dibromo dinitro derivate of fluorescein.

Use in histology

Eosin is most often used as a counterstain to haematoxylin in H&E (haematoxylin and eosin) staining. H&E staining is one of the most commonly used techniques in histology. Tissue stained with hematoxylin and eosin shows cytoplasm stained pink-orange and nuclei stained darkly, either blue or purple. Eosin also stains red blood cells intensely red. Eosin is an acidic dye and shows up in the basic parts of the cell, ie the cytoplasm. Hematoxylin however is a basic dye and shows up in the acidic part of the cell. For example the nucleus, where nucleic acids (DNA and RNA) are concentrated.

For staining, eosin Y is typically used in concentrations of 1 to 5 percent weight by volume, dissolved in water or ethanol. For prevention of mold growth in aqueous solutions, thymol is sometimes added. A small concentration (0.5 percent) of acetic acid usually gives a deeper red stain to the tissue.

Etymology

The name Eosin comes from Eos, the Greek word for 'dawn' and the name of the Greek Goddess of the Dawn.

See also

• Hematoxylin
• H&E stain
• Romanowsky stain

References

• Jocelyn H. Bruce-Gregorios, M.D.: Histopathologic Techniques, JMC Press Inc., Quezon City, Philippines, 1974.

External links

• Eosin Y - Applications information