Used for detecting DNA fragmentation in apoptotic cells through fluorescence labeling of DNA strand breaks. The assay labels 3'-hydroxyl termini of broken DNA strands with fluorescent dye, allowing visualization under a fluorescence microscope or analysis by flow cytometry. Commonly applied in cancer research, toxicology studies, and developmental biology to assess programmed cell death in tissues or cell cultures. The 640 nm fluorescence provides good tissue penetration and compatibility with standard red laser channels, enabling multiplexing with other fluorescent markers. Suitable for use in both fixed cells and paraffin-embedded tissue sections.