What is "safranin"

Polychroite \Pol"y*chro*ite\, n. [Poly- + Gr. ? color: cf. F. polychro["i]te.] (Chem.) The coloring matter of saffron; -- formerly so called because of the change of color on treatment with certain acids; -- called also crocin, and safranin.

n. A biological stain used in histology and cytology.

n. any of a class of chiefly red organic dyes [syn: safranine, saffranine]

Safranin (also Safranin O or basic red 2) is a biological stain used in histology and cytology. Safranin is used as a counterstain in some staining protocols, colouring all cell nuclei red. This is the classic counterstain in both Gram stains, and endospore staining. It can also be used for the detection of cartilage, mucin and mast cell granules.

Safranin typically has the chemical structure shown at right (sometimes described as dimethyl safranin). There is also trimethyl safranin, which has an added methyl group in the ortho- position of the lower ring. Both compounds behave essentially identically in biological staining applications, and most manufacturers of safranin do not distinguish between the two. Commercial safranin preparations often contain a blend of both types.

Safranin is also used as redox indicator in analytical chemistry.