Auramine O is a diarylmethane dye used as a fluorescent stain.
In its pure form, Auramine O appears as yellow needle crystals.
It is insoluble in water and soluble in ethanol and DMSO.
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.
[2] Auramine O can be used together with Rhodamine B as the Truant auramine-rhodamine stain for Mycobacterium tuberculosis.