Amaranth free acid (Acid Red 27 free acid; Azorubin S free acid; FD & C Red Dye No. 2 free acid) is a multifunctional dye. Dyes are important tools in biological experiments. They can help researchers observe and analyze cell structures, track biomolecules, evaluate cell functions, distinguish cell types, detect biomolecules, study tissue pathology and monitor microorganisms. Their applications range from basic scientific research to clinical A wide range of diagnostics. Dyes are also widely used in traditional fields such as textile dyeing, as well as in emerging fields such as functional textile processing, food pigments and dye-sensitized solar cells.