Congo red is a benzidine-based anionic diazo dye, which binds to many amyloid proteins and also interacts with ß-D-glucans, polysaccharides containing continuous ß-(1?4)-linked D-glucopyranosyl units and some hemicellulosic galactoglucomannans.Tested for use in histology. Indicator pH 3.0 - 5.2 blue-reddish orange. Congo red is a benzidine-based anionic diazo dye, which binds to many amyloid proteins and also interacts with ß-D-glucans, polysaccharides containing continuous ß-(1?4)-linked D-glucopyranosyl units and some hemicellulosic galactoglucomannans.Tested for use in histology. Indicator pH 3.0 - 5.2 blue-reddish orange.