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Class: Fluorone
Ionisation: Acid

Chemical structure of Fluorescein

Common Name: Fluorescein
Suggested Name: Fluorescein
Other Names:

C.I. Number: 45350
C.I. Name: Solvent yellow 94
Color: Yellow
Solubility Aqueous: Slight
Solubility Ethanol: Slight
Absorption Maximum: 493.5, 460 485 (Gurr)
Empirical Formula: C20H12O5
Formula Weight: 332.3


Fluorescein is the precursor of the group of dyes collectively referred to as the eosins, but has little use itself in light microscopy even though it is strongly fluorescent. It is used to detect contamination in water supplies because of the intense fluorescence at low concentration. The closely related fluorescein isothiocyanate, is attached to antibodies and used as a fluorescent marker in immunofluorescence microscopy.

Uranin is the sodium salt of fluorescein.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.
  2. Aldrich chemical catalogue, 1992
    Aldrich Chemical Company, Milwaukee, WI, USA.
  3. Susan Budavari, Editor,
    The Merck Index, Ed. 12
    Merck & Co., Inc., Whitehouse Station, NJ, USA
  4. Edward Gurr, 1971
    Synthetic dyes in biology, medicine and chemistry
    Academic Press, London, England.