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.
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
, bromofluoresceic acid
, D&C Red No. 22
); it has a very slightly yellowish cast. The other eosin compound is eosin B
, Acid Red 91
, C.I. 45400
, 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
in H&E (haematoxylin and eosin) staining
. H&E staining is one of the most commonly used techniques in histology
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
) 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.
The name Eosin comes from Eos
, the Greek word for 'dawn' and the name of the Greek Goddess of the Dawn.
- Jocelyn H. Bruce-Gregorios, M.D.: Histopathologic Techniques, JMC Press Inc., Quezon City, Philippines, 1974.