FITC (fluorescein-5-isothiocyanate) is an amine-reactive fluorescein derivative for labeling proteins or other molecules containing primary amines.    &lamba;Ex/&lamba;Em= 492/520 nm  ε = 75,000  Orange solid soluble in DMF or DMSO  Store at -20°C and protect from light, especially in solution  C21H11NO5S.  MW: 389.4  3326-32-7]