Auramine O

Auramine O is a diarylmethane dye used as a fluorescent stain. In its pure form, Auramine O appears as yellow needle crystals. It is very soluble in water and soluble in ethanol.

Auramine O can be used to stain acid-fast bacteria (e.g. Mycobacterium, where it binds to the mycolic acid in its cell wall) in a way similar to Ziehl-Neelsen stain. It can also be used as a fluorescent version of Schiff reagent.