Safranin O

Safranin O, also known as Basic Red 2, is a basic, cationic, and metachromatic azine dye used as a biological stain. The characteristic azine chromophore contains the phenazine, a planar, tricyclic dibenzopyrazine, which consists of two non-planar benzene rings linked by two nitrogen atoms. A delocalized positive charge, an alternation of aromatic and quinonoid structures, and diazotizable amine groups constitute the chromophoric system. c-Methylation makes this dye of moderate overall size. The trimethyl cationic form of safranine is lipophilic, whereas the dimethyl forms are weakly hydrophilic. The dye is commercially available as a chloride.

Safranin O is widely employed as a microbiological stain, especially as a counterstain in Gram staining to distinguish Gram-positive from Gram-negative micro-organisms, and for staining bacterial spores.

• It is used for human-medical cell diagnosis and serves the purpose of the bacteriological investigation of sample material of human origin.
• It is used to prepare a staining solution, that when used together with other in vitro diagnostic products from our portfolio dyes target structures (e. g. Gram-positive or Gram-negative bacteria, by fixing, where necessary embedding, staining, counterstaining, mounting) in bacteriological specimen materials (for example: smears of bacteriological material that have been air-dried and heat-fixed like sputum, smears from fine needle aspiration biopsies (FNAB), rinses, imprints, effusions, pus, exsudates, liquid and solid cultures), for diagnostic evaluations.
• It is used to demonstrate glycosaminoglycans in human and animal histological specimens and nuclei.
• It is a component of Benda′s polychrome stain.
• It is a component of various polychromes and lignin stains for botanical staining applications.
• It has also been applied for the demonstration of mast cells in cytospin preparations and staining surgical frozen sections.

In microbiology, Gram staining allows fast differentiation of bacteria as Gram-positive or Gram-negative. The mureine structure of the bacteria cell wall is the basis of the color affinity. In the first step, bacteria will be stained with crystal violet, an aniline dye. After the treatment with iodine solution (Lugol’s solution), a dye-iodine complex will form. During the decolorizing step, this complex stays in the multilayer mureine structure of the cell wall of Gram-positive bacteria and appears blue-violet. Gram-negative bacteria, by contrast, have a cell wall consisting of a single-layered murein structure, and correspondingly re-release the staining dye after treatment with the decoloring solution. Gram-negative bacteria will be counterstained with safranin solution and will then appear pink to red.