Safranin O is a biological stain commonly used as a counter stain for gram-negative bacteria in the Gram stain procedure. Safranin O has been observed to bind to DNA at a pH 2.21. In the Flemming triple stain procedure Safranin O is used to stain for chromosomes. In late Palaeozoic pteridosperm cuticles Safranin O has shown increased contrast, emphasized cutinization differences, and enhanced the three-dimensional morphology of complex epidermal features when compared with other dyes. The compound has also been used with alcian blue in the histochemical study of the distribution and morphometric characteristics of mast cells. Safranin O has also been used to detect mucin and cartilage.