FITC marker peptides is widely applied in biology research, it's not radioactive. For the main chain of the polypeptide position marked FITC, need to connect a first in the peptide chain amino caproic acid arm to avoid FITC cut off by a TFA in cutting process, because the FITC connected directly on the main chain of the peptide chain amino is unstable, and for side chain amino can be directly connected FITC above.