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. As can be seen from the structural formulae, this process replaces an amino 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.
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.
Famous quotes containing the words nile and/or red:
“Hard by the lilied Nile I saw
A duskish river dragon stretched along.
The brown habergeon of his limbs enamelled
With sanguine alamandines and rainy pearl:
And on his back there lay a young one sleeping,
No bigger than a mouse;”
—Thomas Lovell Beddoes (1803–1849)
“To motorists bound to or from the Jersey shore, Perth Amboy consists of five traffic lights that sometimes tie up week-end traffic for miles. While cars creep along or come to a prolonged halt, drivers lean out to discuss with each other this red menace to freedom of the road.”
—For the State of New Jersey, U.S. public relief program (1935-1943)