Nile Red

Nile red is a common lipid dye. Nile red is a hydrophobic and metachromatic dye with poor solubility and fluorescence in water, with colour emission varying from deep red to strong yellow gold in hydrophobic environments ^[1].

Nile red can dye the cholesterol in the human plasma through staining of lipid vesicles in smooth muscle cells and in cultured macrophages incubated at low density, using the excitation/emission wavelengths 450 to 500/>528 ^[2]. Nile red was also used to study membrane heterogeneity ^[3] and ligand-hydrophobic protein surface interactions with the alternative wavelengths 570/610 ^[4] and to study enzyme mechanism by using the wavelengths 550/640 to 660 ^[5]. Nile red has also been successfully used to stain intracellular neutral lipids that is, TAG and cholesterol esters in yeast, fungi with coupled wavelengths 488/565 to 585 ^[6] and also in microalgae, with wavelengths set to 488 to 525/570 to 600 ^[7] or to stain total lipids with wavelengths set to 490/585 ^[8].

References:
[1]. Rumin J, Bonnefond H, Saint-Jean B, et al. The use of fluorescent Nile red and BODIPY for lipid measurement in microalgae[J]. Biotechnology for biofuels, 2015, 8(1): 1-16.
[2]. Greenspan P, Mayer E P, Fowler S D. Nile red: a selective fluorescent stain for intracellular lipid droplets[J]. The Journal of cell biology, 1985, 100(3): 965-973.
[3]. Ira and, Krishnamoorthy G. Probing the link between proton transport and water content in lipid membranes[J]. The Journal of Physical Chemistry B, 2001, 105(7): 1484-1488.
[4]. Sackett D L, Wolff J. Nile red as a polarity-sensitive fluorescent probe of hydrophobic protein surfaces[J]. Analytical biochemistry, 1987, 167(2): 228-234.
[5]. Ruvinov S B, Yang X J, Parris K D, et al. Ligand-mediated Changes in the Tryptophan Synthase Indole Tunnel Probed by Nile Red Fluorescence with Wild Type, Mutant, and Chemically Modified Enzymes (∗)[J]. Journal of Biological Chemistry, 1995, 270(11): 6357-6369.
[6]. Kimura K, Yamaoka M, Kamisaka Y. Rapid estimation of lipids in oleaginous fungi and yeasts using Nile red fluorescence[J]. Journal of microbiological methods, 2004, 56(3): 331-338.
[7]. Cooksey K E, Guckert J B, Williams S A, et al. Fluorometric determination of the neutral lipid content of microalgal cells using Nile Red[J]. Journal of microbiological methods, 1987, 6(6): 333-345.
[8]. Lee S J, Yoon B D, Oh H M. Rapid method for the determination of lipid from the green alga Botryococcus braunii[J]. Biotechnology techniques, 1998, 12(7): 553-556.