Fluorescein isothiocyanate (FITC), a fluorophor, reacts with amino groups. A spacer (at least β-alanine) has to to inserted when tagging a peptide with FITC at its N-terminus. N-terminal Nα-FITC-labeled amino acids will be split off when the peptide is treated with acid.
Excitation 490 nm, emission 520 nm.