MCE One Step TUNEL Apoptosis Detection Kit (FITC) provides a rapid and convenient method to detect cell apoptosis. When cells undergo apoptosis, specific DNA endonucleases will be activated, cutting the genomic DNA between the nucleosomes. The DNA of apoptotic cells is cleaved into multimers of 180-200 bp fragments. The exposed 3'-OH of the broken DNA can be catalyzed by Terminal Deoxynucleotidyl Transferase (TdT) with fluorescein labeled dUTP, which can be detected with fluorescence microscope or flow cytometer. The maximum excitation wavelength and emission wavelength of FITC were 488 nm and 525 nm respectively.