Congo Red

Property Data Common name Suggested name Other names   C.I. number C.I. name Class Ionisation Solubility aqueous Solubility ethanol Absorption maximum   Colour Empirical formula Formula weight Congo red Congo red Direct red Cotton red 22120 Direct red 28 Azo Acid Readily 0.19% 497 (Conn, Aldrich), 488 (Merck), 486 (Gurr) Red C32H22N6O6S2Na2 696.7

Congo red is used to stain amyloid. It is believed that it hydrogen bonds to the beta pleated sheet structure of amyloid with the dye molecules aligned in a very regular manner. This forms a "pseudocrystal", which results in a characteristic, green birefringence of the stained amyloid.

 

Reference
R. D. Lillie.
Conn's Biological Stains
Williams & Wilkins, Baltimore, MD., U.S.A.

Edward Gurr, (1971)
Synthetic dyes in biology, medicine and chemistry
Academic Press, London, England.

Aldrich chemical catalogue, 1992
Aldrich Chemical Company, Milwaukee, WI, USA.

Susan Budavari, Editor, (1996)
The Merck Index, Ed. 12
Merck & Co., Inc., Whitehouse Station, NJ, USA