Fluorescein isothiocyanate (FITC) labeling is a common technique with a wide range of? applications because it reacts quickly with amines and due to its high quantum efficacy. Due to its high molecular absorptivity, using FITC labels is preferred over conventional colorimetric labels and radio labels because fluorophores like FITC are bright, easier to work with, and don’t require special waste handling. Proteins, substrates, peptide hormones, and antibodies? labeled by FITC can be used as probes in flow cytometry, enzyme kinetics, and immunocytochemistry, as well as in the detection of receptors on the surface of? the target cells. 5-FAM is the purified single isomer of carboxyfluorescein. It is one of the most popular green fluorescent reagents used for labeling peptides, proteins and nucleotides. It has been predominantly used to develop a variety of green fluorescent peptides that can be excited with the 488 nm line of the Ar laser. It has also been used to prepare various small fluorescent molecules. 6-FAM (6-Carboxyfluorescein) contains a carboxylic acid that can be used to react with primary amines via carbodiimide activation of the carboxylic acid. Fluorescein is the most common fluorescent derivatization reagent for labeling biomolecules. In addition to its relatively high absorptivity, excellent fluorescence quantum yield, and good water solubility, fluorescein has an excitation maximum that closely matches the 488 nm spectral line of the argon-ion laser.