Eosin
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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.<ref name="Lillie, 1977" /><ref name="Bancroft and Stevens, 1982" />
History and etymologyEdit
Eosin was named by its inventor Heinrich Caro after the nickname (Eos) of a childhood friend, Anna Peters.<ref>Template:Cite journal</ref> It was commercialized (mainly for the textile industry) in 1874, in the same year when it was invented.<ref>Template:Cite book</ref>
VariantsEdit
There are actually two very closely related compounds commonly referred to as eosin. Most often used is in histology is eosin Y,<ref name="Lillie, 1977" /><ref name="Bancroft and Stevens, 1982" /> 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,<ref>Template:Cite book</ref> Eosin J<ref>Template:Cite book</ref> or iodo-eosine<ref>Template:Cite book</ref> but is now called erythrosine or Red 3.
UsesEdit
Use in histologyEdit
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 nuclei stained darkly, either blue or purple. Eosin also stains red blood cells intensely red.
For staining, eosin Y is typically used in concentrations of 1 to 5 percent weight by volume, dissolved in water or ethanol.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> For prevention of mold growth in aqueous solutions, thymol is sometimes added.<ref>Template:Cite journal</ref> A small concentration (0.5 percent) of acetic acid usually gives a deeper red stain to the tissue.
It is listed as an IARC class 3 carcinogen.
Other usesEdit
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.<ref name=Dyefade>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> A notable user of eosin dye was the Post-Impressionist painter Van Gogh.
See alsoEdit
ReferencesEdit
External linksEdit
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