Cell Counting Kit-8, referred to as CCK8 (or WST-8) kit, is based on WST-8 (chemical name: 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrobenzene) A rapid and highly sensitive detection kit for cell proliferation and cytotoxicity. Working principle of WST-8: In the presence of electronic coupling reagent, it can be reduced by dehydrogenase in mitochondria to produce highly water-soluble orange-yellow formazan product (formazan). The intensity of the color is directly proportional to cell proliferation and inversely proportional to cytotoxicity. Use a microplate reader to measure the OD value at a wavelength of 450 nm, which indirectly reflects the number of living cells. WST-8 is an upgraded replacement product of MTT, which has obvious advantages compared with MTT or other MTT similar products such as XTT and MTS. First of all, the formazan produced by the reduction of MTT by some dehydrogenases in the mitochondria is not water-soluble and requires a specific solution to dissolve; while the formazan produced by WST-8, XTT and MTS are all water-soluble, which can save energy. Go to the subsequent dissolution step. Secondly, the formazan produced by WST-8 is more soluble than the formazan produced by XTT and MTS. Third, WST-8 is more stable than XTT and MTS, making the experimental results more stable. In addition, WST-8 has a wider linear range and higher sensitivity than MTT and XTT. The CCK method is widely used in drug screening, cell proliferation determination, cytotoxicity determination, tumor drug sensitivity test, and biological factor activity detection.