Fluorescein isothiocyanate (FITC) is an amine-reactive derivative of fluorescein dye that has wide-ranging applications as a label for antibodies and other probes, for use in fluorescence microscopy, flow cytometry and immunofluorescence-based assays such as Western blotting and ELISA.

• Alternative names: 5/6-FITC
• Chemical name: 5(6)-fluorescein isothiocyanate mixed isomer
• Molecular weight: 389.2
• Excitation source: 488 nm spectral line, argon-ion laser
• Excitation wavelength: 494 nm
• Emission wavelength: 518 nm
• Extinction coefficient: > 70,000 M^-1cm^-1
• CAS #: 27072-45-3
• Purity: > 95% by HPLC
• Solubility: Soluble in aqueous buffers at pH > 6
• Reactive groups: Isothiocyanate, reacts with primary amines at pH 7.0 to 9.0
• Store desiccated at -20˚C, protect from moisture

The isothiocyanate variety of fluorescein efficiently labels antibodies and other purified proteins at primary amines (lysine side chains).

Applications
Label antibodies for use as immunofluorescent probes
Label oligonucleotides for hybridization probes
Detect proteins in gels and on Western blots