Auramine O

Technical Specifications

Product Description & Scientific Applications

Auramine O (Basic Yellow 2; C.I. 41000) is a fluorescent cationic dye and a molecular rotor, built from two 4-(dimethylamino)phenyl arms joined at a central carbon.

Common Scientific Applications

Acid-fast fluorescence stain. Auramine O stains acid-fast bacilli, including Mycobacterium tuberculosis, in sputum smears read by fluorescence microscopy. As a fluorochrome method it detects mycobacteria more sensitively than the Ziehl–Neelsen carbol-fuchsin stain and is quicker to screen; it is used as the auramine-phenol stain and, combined with rhodamine, as the auramine-rhodamine stain, under both mercury-vapour and LED excitation. The same auramine-phenol method screens faecal smears for Cryptosporidium oocysts.

Fluorescent molecular rotor. In low-viscosity solution Auramine O is weakly fluorescent and short-lived, because the excited dye decays without emitting, through intramolecular rotation. Hindering that rotation — by high viscosity, a rigid matrix, or adsorption onto a surface such as cellulose — sharply raises both the fluorescence intensity and the excited-state lifetime. Its emission therefore reports the rigidity of the dye's immediate environment.

Amyloid and protein binding. Binding to amyloid fibrils switches on Auramine O fluorescence through the same restriction of rotation, which has prompted its investigation as an alternative to thioflavin T. Selectivity for fibrils is limited: the dye also binds non-amyloid proteins such as serum albumin with strong emission enhancement, lowering the contrast between native and aggregated protein.

Light-up aptamer reporter. A DNA "light-up" aptamer binds Auramine O in its loop and restricts its rotation, turning the fluorescence on. This binding-induced signal makes Auramine O a label-free reporter in CRISPR/Cas12a biosensors. In one design a split aptamer reassembles to raise the emission; in another a hairpin aptamer is cleaved by Cas12a to lower it. Reported targets include site-specific DNA methylation for colorectal-cancer screening and the SARS-CoV-2 nucleocapsid protein.

Plant cuticle stain. Auramine O is a fluorescent stain for the plant cuticle. Under confocal microscopy it resolves cuticle architecture and deposition, and distinguishes wild-type tissue from cutin-deficient mutants in tomato (Solanum lycopersicum).

Shipping Destinations

• EU: Priority delivery, 2–5 business days.
• United Kingdom: 3–7 business days.
• Norway (DDP): 3–7 business days, duties and taxes prepaid.
• Switzerland (DDP): 3–7 business days, duties and taxes prepaid.
• Classified as dangerous goods — shipping restrictions apply outside the above destinations.