Cell Counting Kit-8 (CCK-8) Assay

The Cell Counting Kit-8 (CCK-8) assays through the use of the highly water-soluble tetrazolium salt WST-8 [2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt], which produces a water-soluble formazan dye when reduced in the presence of an electron mediator, as illustrated in Fig. 1. CCK-8 is provided as a one-bottle solution, eliminating the need for pre-mixing components. This non-radioactive Cell Counting Kit-8 facilitates sensitive colorimetric assays for determining the count of viable cells in cell proliferation and cytotoxicity experiments.

WST-8 undergoes reduction by cellular dehydrogenases, yielding an orange-colored formazan product that remains soluble in the culture medium. The quantity of formazan dye generated by cellular dehydrogenase activity is directly proportional to the number of viable cells. The detection sensitivity of CCK-8 surpasses that of other tetrazolium salts such as MTT, XTT, MTS, or WST-1.