Nile red explained

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 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]

Synthesis

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.

Notes and References

  1. Plenderleith . Richard . Swift . Thomas . Rimmer . Stephen . Highly-branched poly(N-isopropyl acrylamide)s with core–shell morphology below the lower critical solution temperature . RSC Advances . 2014 . 4 . 92 . 50932–50937 . 10.1039/C4RA10076J . 10454/11180 . free .
  2. Greenspan . P . Mayer . E P . Fowler . S D . Nile red: a selective fluorescent stain for intracellular lipid droplets. . The Journal of Cell Biology . 1 March 1985 . 100 . 3 . 965–973 . 10.1083/jcb.100.3.965 . 3972906 . 2113505 .
  3. News: Plastic: WHO launches health review . 15 March 2018 . David Shukman . BBC News Online.
  4. Mason . Sherri A. . Welch . Victoria G. . Neratko . Joseph . Synthetic Polymer Contamination in Bottled Water . Frontiers in Chemistry . 11 September 2018 . 6 . 407 . 10.3389/fchem.2018.00407 . 30255015 . 6141690 . 2018FrCh....6..407M . free .
  5. Khalilian . Alireza . Khan . Md. Rajibur Rahaman . Kang . Shin-Won . Highly sensitive and wide-dynamic-range side-polished fiber-optic taste sensor . Sensors and Actuators B: Chemical . 1 October 2017 . 249 . 700–707 . 10.1016/j.snb.2017.04.088 .
  6. Web site: Fluorescence SpectraViewer - Nile Red triglycerides . Thermo Fisher Scientific . 2017-05-17 . 2020-03-06.
  7. Web site: Fluorescence SpectraViewer - Nile Red phospholipids . Thermo Fisher Scientific . 2017-05-17 . 2020-03-06.
  8. Shafiee . Omid . Jenkins . Samantha G. . Ito . Takashi . Higgins . Daniel A. . 2023-01-27 . Diffusion of hydrophilic to hydrophobic forms of Nile red in aqueous C12EO10 gels by variable area fluorescence correlation spectroscopy . Physical Chemistry Chemical Physics . en . 25 . 4 . 2853–2861 . 10.1039/D2CP05578C . 1463-9084.
  9. Fowler . S. D. . Greenspan . P. . 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 . 5 January 2017 . 33 . 8 . 833–836 . 10.1177/33.8.4020099 . 4020099 . 10496865 . free .
  10. Park . So-Yeon . Kubota . Yasuhiro . Funabiki . Kazumasa . Shiro . Motoo . Matsui . Masaki . Near-infrared solid-state fluorescent naphthooxazine dyes attached with bulky dibutylamino and perfluoroalkenyloxy groups at 6- and 9-positions . Tetrahedron Letters . 11 March 2009 . 50 . 10 . 1131–1135 . 10.1016/j.tetlet.2008.12.081 .

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