Merck, F7250-5G, Fluorescein isothiocyanate isomer I

Fluorescein isothiocyanate (FITC) is yellow-orange in color with an absorption maximum at 495nm. Upon excitation, it emits a yellow-green color with an emission maximum at 525nm. It is widely used to attach a fluorescent label to proteins via the amine group. The isothiocyanate group reacts with amino terminal and primary amines in proteins. It has been used for the labeling of proteins including antibodies and lectins. Fluorescein isothiocyanate isomer I has been proposed as a contact sensitizer.