https://www.creative-bioarray.com/support/tunel-apoptosis-assay-chromogenic.htm The TUNEL assay relies on the TdT enzyme to catalyze the addition of labeled dUTP to the 3'-hydroxyl (3'-OH) ends of cleaved DNA fragmentations. Labeled dUTP such as biotin-dUTP can be recognized using secondary reagent streptavidin through colorimetric detection.All Rights Reserved