Nile red (also known as Nile blue oxazone) is a lipophilic stain. Nile red stains intracellular lipid droplets yellow. In most polar solvents, Nile red will not fluoresce; however, when in a lipid-rich environment, it can be intensely fluorescent, with varying colors from deep red (for polar membrane lipid) to strong yellow-gold emission (for neutral lipid in intracellular storages). The dye is highly solvatochromic and its emission and excitation wavelength both shift depending on solvent polarity[1] and in polar media will hardly fluoresce at all.[2]

Nile red
Preferred IUPAC name
Other names
Nile red, Nile blue oxazone
3D model (JSmol)
ECHA InfoCard 100.028.151 Edit this at Wikidata
  • InChI=1S/C20H18N2O2/c1-3-22(4-2)13-9-10-16-18(11-13)24-19-12-17(23)14-7-5-6-8-15(14)20(19)21-16/h5-12H,3-4H2,1-2H3 checkY
  • InChI=1/C20H18N2O2/c1-3-22(4-2)13-9-10-16-18(11-13)24-19-12-17(23)14-7-5-6-8-15(14)20(19)21-16/h5-12H,3-4H2,1-2H3
  • CCN(CC)c1ccc2c(c1)oc-3cc(=O)c4ccccc4c3n2
Molar mass 318.376 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Nile red has applications in cell biology, where it can be used as a membrane dye which can be readily visualized using an epifluorescence microscope with excitation and emission wavelengths usually shared with red fluorescent protein. Nile red has also been used as part of a sensitive detection process for microplastics in bottled water.[3][4] Additionally, nile red is a remarkable candidator in fabricating membrane for different sensors to detect environmental changes, such as taste, gas, pH, etc.[5]

In triglycerides (a neutral lipid), Nile red has an excitation maximum of about 515 nm (green), and emission maximum of about 585 nm (yellow-orange).[6] In contrast, in phospholipids (polar lipids), Nile red has an excitation maximum of about 554 nm (green), and an emission maximum of about 638 nm (red).[7]

The diffusion coefficient of Nile red in ethanol has been reported 470 μm2/s.[8]


Nile red can be prepared through acid hydrolysis by boiling a solution of Nile blue with sulfuric acid.[9] This process replaces an iminium group with a carbonyl group. Alternatively, Nile red and its analogs (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.[10] 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.


  1. ^ Plenderleith, Richard; Swift, Thomas; Rimmer, Stephen (2014). "Highly-branched poly(N-isopropyl acrylamide)s with core–shell morphology below the lower critical solution temperature". RSC Advances. 4 (92): 50932–50937. doi:10.1039/C4RA10076J. hdl:10454/11180.
  2. ^ Greenspan, P; Mayer, E P; Fowler, S D (1 March 1985). "Nile red: a selective fluorescent stain for intracellular lipid droplets". The Journal of Cell Biology. 100 (3): 965–973. doi:10.1083/jcb.100.3.965. PMC 2113505. PMID 3972906.
  3. ^ David Shukman (15 March 2018). "Plastic: WHO launches health review". BBC News Online.
  4. ^ Mason, Sherri A.; Welch, Victoria G.; Neratko, Joseph (11 September 2018). "Synthetic Polymer Contamination in Bottled Water". Frontiers in Chemistry. 6: 407. Bibcode:2018FrCh....6..407M. doi:10.3389/fchem.2018.00407. PMC 6141690. PMID 30255015.
  5. ^ Khalilian, Alireza; Khan, Md. Rajibur Rahaman; Kang, Shin-Won (1 October 2017). "Highly sensitive and wide-dynamic-range side-polished fiber-optic taste sensor". Sensors and Actuators B: Chemical. 249: 700–707. doi:10.1016/j.snb.2017.04.088.
  6. ^ "Fluorescence SpectraViewer - Nile Red triglycerides". Thermo Fisher Scientific. 17 May 2017. Retrieved 6 March 2020.
  7. ^ "Fluorescence SpectraViewer - Nile Red phospholipids". Thermo Fisher Scientific. 17 May 2017. Retrieved 6 March 2020.
  8. ^ Shafiee, Omid; Jenkins, Samantha G.; Ito, Takashi; Higgins, Daniel A. (27 January 2023). "Diffusion of hydrophilic to hydrophobic forms of Nile red in aqueous C12EO10 gels by variable area fluorescence correlation spectroscopy". Physical Chemistry Chemical Physics. 25 (4): 2853–2861. doi:10.1039/D2CP05578C. ISSN 1463-9084.
  9. ^ Fowler, S. D.; Greenspan, P. (5 January 2017). "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 & Cytochemistry. 33 (8): 833–836. doi:10.1177/33.8.4020099. PMID 4020099. S2CID 10496865.
  10. ^ Park, So-Yeon; Kubota, Yasuhiro; Funabiki, Kazumasa; Shiro, Motoo; Matsui, Masaki (11 March 2009). "Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions". Tetrahedron Letters. 50 (10): 1131–1135. doi:10.1016/j.tetlet.2008.12.081.