The Click-iT™ TUNEL Colorimetric IHC Detection Kit is used to identify apoptotic cells in tissue and cultured cell samples through the use of a small, highly specific labeling moiety and streptavidin-peroxidase conjugation. After incorporation of the labeling moiety into sites of DNA fragmentation, detection is achieved through a catalyzed 'click' reaction that adds a biotin group at these sites. The subsequent addition of a streptavidin-peroxidase and peroxidase substrate results in a dark brown signal that can be detected with light microscopy and stored for future analysis.

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• Optimized for the detection of apoptotic cells in either tissue or cell samples
• Improved colorimetric TUNEL assay—better label incorporation due to small reactive moiety
• Increased sensitivity—specific label incorporation results in lower background and brighter signal
• Content-rich results—cell morphology, cellular environment, and apoptotic signal are clearly visible
• Flexibility—the assay can be configured for 50 independent TUNEL apoptosis tests

The later stages of apoptosis are characterized by changes in nuclear morphology, chromatin condensation, nuclear envelope degradation, and DNA fragmentation. Terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL) assays are based on the incorporation of modified dUTPs by terminal deoxynucleotidyl transferase (TdT) at the 3’-OH ends of fragmented DNA. Colorimetric TUNEL assays utilize dUTPs conjugated with a biotin moiety, followed by the addition of a streptavidin-peroxidase conjugate and peroxidase substrate, resulting in a dark brown apoptotic signal. However, colorimetric TUNEL assays are prone to high background, which reduces the sensitivity and specificity of the signal.

The Click-iT TUNEL Colorimetric IHC Detection Kit was developed to address these issues by utilizing a dUTP modified with an alkyne group (a small bio-orthogonal functional group) that enables the nucleotide to be more readily incorporated by TdT. After incorporation, a highly specific click reaction covalently links biotin azide and the alkyne group. Streptavidin-peroxidase (horseradish peroxidase) followed by peroxidase substrate (DAB) are added, allowing colorimetric detection of apoptotic cells. The high degree of labeling specificity inherent in the click technology results in low background and improved detection of apoptotic cells.

The Click-iT TUNEL Colorimetric IHC Detection Kit has been optimized and contains all of the reagents needed for detection of apoptotic cells from either tissue or cell samples. The reagents supplied in this kit can be used to test 50 samples and configured to test from one to 50 samples at a time.