Used as a direct (or substantive) dye for cotton, paper, and leather due to its strong affinity for cellulose materials. Commonly applied in textile industries for dyeing without the need for mordants. Also employed as a pH indicator, turning blue in acidic solutions (below pH 3.0) and red in neutral to basic conditions (above pH 5.0). Widely utilized in histology to stain amyloid deposits in tissues, which exhibit apple-green birefringence under polarized light when bound to Congo red. Has been used in research to detect protein aggregation, particularly in studies related to Alzheimer's and other amyloid-related diseases. Additionally, explored in environmental applications for the removal of heavy metals and dyes from wastewater using adsorption techniques.