Eosin is the name of several fluorescent acidic compounds which bind to and from salts with basic, or eosinophilic, compounds like proteins containing basic amino acid residues such as histidine, arginine and lysine, and stains them dark red or pink as a result of the actions of bromine on eosin. In addition to staining proteins in the cytoplasm, it can be used to stain collagen and muscle fibers for examination under the microscope. Structures that stain readily with eosin are termed eosinophilic. In the field of histology, Eosin Y is the form of eosin used most often as a histologic stain.
History and etymology
Eosin was named by its inventor
Heinrich Caro after the nickname (
Eos) of a childhood friend, Anna Peters.
It was commercialized (mainly for the textile industry) in 1874, in the same year when it was invented.
Variants
There are actually two very closely related compounds commonly referred to as
eosin. Most often used is in
histology is
eosin Y,
which is a tetra-bromo derivative of
fluorescein and has a very slightly yellowish cast. It is also known as
eosin Y ws, eosin yellowish, Acid Red 87, C.I. 45380, bromoeosine, bromofluoresceic acid, and D&C Red No. 22. The other eosin compound is
eosin B, which is a dibromo derivative and has a very faint bluish cast. It is also known as eosin bluish, Acid Red 91, C.I. 45400, Saffrosine, Eosin Scarlet, and imperial red. The two dyes are interchangeable, and the use of one or the other is a matter of preference and tradition.
Food dye tetraiodofluorescein was historically known as Bluish Eosine,
Uses
Use in histology
Eosin is most often used as a
counterstain to
hematoxylin in H&E (haematoxylin and eosin) staining. H&E staining is one of the most commonly used techniques in
histology. Tissue stained with
haematoxylin and eosin shows
cytoplasm stained pink-orange and
cell nucleus stained darkly, either blue or purple. Eosin also stains
erythrocyte intensely red.
For staining, eosin Y is typically used in concentrations of 1 to 5 percent weight by volume, dissolved in water or ethanol.
It is listed as an IARC class 3 carcinogen.
Other uses
Eosin is also used as a red dye in inks; however, the molecule, especially that of eosin Y, tends to degrade over time, leaving behind its bromine atoms, hence causing paint incorporating such a dye to obtain a darker brown tinge over time.
A notable user of eosin dye was the Post-Impressionist painter
Van Gogh.
See also
External links
