Safranin is used as a dye for textiles and as a stain for various scientific procedures. Scientific procedures that involve safranin include Gram counterstaining, endospore counterstaining, granule detection and redox indication.
Safranin is a red, water-soluble dye also referred to as phenosafranine, basic red 2 and Safranin 0. It is capable of staining all cell nuclei red. Safranin is available as dimethyl or trimethyl safranin, which are basically identical in behavior and appearance.
Safranin is commonly used in Gram staining, which helps distinguish between Gram-positive and Gram-negative bacteria groups due to cell wall composition. Both groups are first stained with a water-soluble crystal violet dye and iodine is added to the solution. Ethyl alcohol or acetone is then added, which causes the Gram-positive bacteria to retain the crystal violet dye and the Gram-negative bacteria to discard the crystal violet dye. Next, safranin is added as a counterstain for the bacteria, staining the Gram-negative bacteria red. The Gram-positive bacteria remain violet.
The cell walls of Gram-positive bacteria contain a thick layer of peptidoglycan, which enables the bacteria to retain the crystal violet stain. Gram-negative bacteria retain the safranin stain rather than the violet stain due to their thinner peptidoglycan cell walls.