Fluorescein isothiocyanate (FITC) is a derivative of

fluorescein Fluorescein is an organic compound and dye based on the xanthene tricyclic structural motif, formally belonging to Triarylmethane dye, triarylmethine dyes family. It is available as a dark orange/red powder slightly soluble in water and alcohol. ...

used in wide-ranging applications including flow cytometry. First described in 1942, FITC is the original fluorescein molecule functionalized with an

isothiocyanate In organic chemistry, isothiocyanate is a functional group as found in compounds with the formula . Isothiocyanates are the more common isomers of thiocyanates, which have the formula . Occurrence Many isothiocyanates from plants are produce ...

reactive group (−N=C=S), replacing a

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

atom on the bottom ring of the structure. It is typically available as a mixture of

isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...

s, fluorescein 5-isothiocyanate (5-FITC) and fluorescein 6-isothiocyanate (6-FITC). FITC is reactive towards nucleophiles including

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

and

sulfhydryl In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...

groups on

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s. It was synthesized by Robert Seiwald and Joseph Burckhalter in 1958. A succinimidyl-ester functional group attached to the fluorescein core, creating "NHS-fluorescein", forms another common amine reactive derivative that has much greater specificity toward primary amines in the presence of other nucleophiles. FITC has excitation and

emission spectrum The emission spectrum of a chemical element or chemical compound is the Spectrum (physical sciences), spectrum of frequencies of electromagnetic radiation emitted due to electrons making a atomic electron transition, transition from a high energ ...

peak wavelengths of approximately 495 nm and 519 nm, giving it a green color. Like most fluorochromes, it is prone to

photobleaching In optics, photobleaching (sometimes termed fading) is the photochemical alteration of a dye or a fluorophore molecule such that it is permanently unable to fluoresce. This is caused by cleaving of covalent bonds or non-specific reactions between ...

. Due to the problem of photobleaching, derivatives of fluorescein such as Alexa 488 and DyLight 488 have been tailored for various chemical and biological applications where greater photostability, higher fluorescence intensity, or different attachment groups are needed. In addition, some experiments make use of FITC's propensity for photobleaching in order to measure proteins' lateral mobility in membranes, through the technique of

fluorescence recovery after photobleaching Fluorescence recovery after photobleaching (FRAP) is a method for determining the kinetics of diffusion through tissue or cells. It is capable of quantifying the two-dimensional lateral diffusion of a molecularly thin film containing fluorescently ...

References

{{DEFAULTSORT:Fluorescein Isothiocyanate Benzoic acids Fluorone dyes Isothiocyanates Staining dyes