Congo red is a high-grade reagent supplied by Micromaster. Few other chemical names used to denote this reagent include, Benzo congo red, C.I. Direct Red 28 and Haemomedica. It is available in the form of a red or brownish red powder solid which is odourless. It is the sodium salt of 3,3′-([1,1′-biphenyl]-4,4′-diyl)bis(4-aminonaphthalene-1-sulfonic acid). Congo red is soluble in water, and ethanol. It is stable if stored according to the recommended conditions. If exposed to excessive heat or in case of burning, it can generate hazardous decomposition products like nitrogen oxides (NOx), Carbon monoxide (CO), Carbon dioxide (CO2), sulphur oxides, and ammonia. Avoid close contact with open flames, hot surfaces, sources of ignition and excessive heat. Congo red is incompatible with strong oxidizing agents, strong acids and strong reducing agents. It may cause eye and skin irritation. It is slightly harmful if inhaled or ingested.

CAS No. 573-58-0
Quantity provided: 25 g/pack
Molecular formula: C32H22N6Na2O6S2
Molecular weight: 696.664 g/mol
Since it changes its colour from blue to red at pH 3.0–5.2, Congo red can be used as a pH indicator. In histology and microscopy, Congo red is used for staining amyloid in the cell walls of plants and fungi, and for the outer membrane of Gram-negative bacteria. Apple-green birefringence of Congo red stained preparations under polarized light is indicative of the presence of amyloid fibrils. It is also used in flux cytometry experiments for the detection of Acanthamoeba, Naegleria and other amoebal cysts.