FITC (Fluorescein isothiocyanate) is the form of fluorescein used for conjugation to all of our antibodies and purified proteins, with the exception of streptavidin. Fluorescein conjugates absorb light maximally at 492 nm and fluoresce maximally at 520 nm. Although less bright than other green-fluorescing dyes, FITC is still a widely used fluorophore due to its long history. The major disadvantage of fluorescein is its rapid photobleaching (fading), which can be mitigated by the use of an anti-fading agent in the mounting medium. A better choice for many applications involving FITC is Alexa Fluor 488 because it is brighter and more photostable.