Fluorescein isothiocyanate (FITC)

Fluorescein isothiocyanate (FITC) is a small, synthetic fluorescent dye derived from fluorescein by substitution with an isothiocyanate group (–N=C=S). It is primarily used as a fluorescent labeling reagent for proteins, antibodies, and other biomolecules through covalent attachment to primary amine groups, often lysine residues, via a stable thiourea bond[2][3][5][6][9]. FITC is used in a variety of analytical techniques including flow cytometry, fluorescence microscopy, immunofluorescence assays, Western blotting, and labeling of nucleic acids[2][3][5][7][9]. It is not a biological macromolecule, receptor, enzyme, or therapeutic target, but a chemical tool; therefore, it should not be considered a therapeutic or pharmacological target. FITC is most often supplied as a mixture of two isomers (5-FITC and 6-FITC)[2][5][9]. Common physical properties are molecular formula C21H11NO5S, molar mass 389.4 g/mol, with excitation/emission maxima at approximately 495/519 nm giving strong green fluorescence[5][6][9]. The isothiocyanate group enables efficient labeling under mild reaction conditions[2][5]. It is highly valued for its ease of conjugation, high fluorescence quantum yield, and broad compatibility with biotechnological applications. FITC can undergo photobleaching and, rarely, may act as a contact sensitizer[3][9]. Fluorescein isothiocyanate is therefore not a receptor or molecular target, but a functional dye and labeling reagent.

Other names

FITCFluorescein isothiocyanate isomer IFluorescein isothiocyanate isomer II5-FITC6-FITC