safranin

Safranin is a basic red dye used in microscopy as a biological stain. The form most commonly used in laboratories is Safranin O, a cationic phenazine dye that binds to negatively charged cellular components. The name derives from its deep saffron-red color, not from saffron spice itself.

Applications: In microbiology, safranin is used as a counterstain in Gram staining. After crystal violet and iodine, Gram-positive cells retain the purple stain, while Gram-negative cells are counterstained pink by safranin, enabling differentiation under a light microscope. Safranin is also employed in histology and botany to stain lignified or proteoglycan-rich tissues. In plant tissue sections, it often stains cellulose and lignin-containing walls red, and is frequently used alongside fast green in double-stain protocols to provide contrast.

Forms and preparation: Safranin O is supplied as an aqueous solution and used at low concentrations, typically around 0.1% for Gram staining. The dye is light-sensitive and should be stored in a dark container to preserve color intensity.

Safety and handling: Safranin is generally handled as a chemical stain with potential irritant effects on skin and eyes. Appropriate laboratory precautions include wearing gloves, eye protection, and proper ventilation, and disposing of waste according to local regulations.

See also: Gram staining, histology, plant histology, fast green.