Nile red

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Nile red
CAS number 7385-67-3 N
PubChem 65182
ChemSpider 58681 YesY
ChEBI CHEBI:52169 YesY
Jmol-3D images Image 1
Molecular formula C20H18N2O2
Molar mass 318.369 g/mol
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references
Nile red under visible and ultraviolet (366 nm) light in different solvents
From left to right: 1. water, 2. methanol, 3. ethanol, 4. acetonitrile, 5. dimethylformamide, 6. acetone, 7. ethyl acetate, 8. dichloromethane, 9. n-hexane, 10. methyl-tert-butylether, 11. cyclohexane, 12. toluene.

Nile red (also known as Nile blue oxazone) is a lipophilic stain. It is produced by boiling a solution of Nile blue with sulfuric acid.[1] As can be seen from the structural formulae, this process replaces an iminium group with a carbonyl group. Nile red stains intracellular lipid droplets red. In most polar solvents Nile Red will not fluoresce, however when in a lipid-rich environment can be intensely fluorescent, with varying colours from deep red to strong yellow-gold emission. Whilst it generally excites at 485 nm, and emits at 525 nm (552/636 nm in methanol), the fluorescence of the dye is heavily dependent on the solvent used, and in some cases does not fluoresce at all.[2]

Since the reaction to generate Nile red does not usually completely exhaust the supply of Nile blue, additional separation steps are required if pure Nile red is needed.

Bacillus subtilis stained with Nile Red as a membrane dye (shown in red). This strain grows partly as cell chains, so a membrane dye may be useful to distinguish internal cell boundaries.

Nile red has applications in cell biology, where it can be used as a membrane dye which can be readily visualised using an epifluorescence microscope with excitation and emission wavelengths usually shared with RFP.


Historically, Nile Red was prepared by acid hydrolysis of the dye Nile Blue. Alternatively, Nile Red and its analogues (naphthooxazine dyes) can be prepared by acid-catalyzed condensation of corresponding 5-(dialkylamino)-2-nitrosophenols with 2-naphthol. The yields are generally moderate as no co-oxidant is used in this procedure:[3]

Nile Red synthesis


  1. ^ SD Fowler and P Greenspan (1985). "Application of Nile red, a fluorescent hydrophobic probe, for the detection of neutral lipid deposits in tissue sections: comparison with oil red O". Journal of Histochemistry and Cytochemistry 33 (8): 833–836. 
  2. ^ P Greenspan, E. P. Mayer and S. D. Fowler (1985). "Nile Red, A Selective Fluorescent Stain for Intracellular Lipid Droplets". Journal of Cell Biology 100 (1): 965–973. 
  3. ^ Park, So-Yeon; Kubota, Y.; Funabiki, K.; Shiro, M.; Matsui, M. (2009). "Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions". Tetrahedron Letters 50: 1131–1135. doi:10.1016/j.tetlet.2008.12.081.