Cell Counting Kit 8 is a rapid and highly sensitive kit widely used for cell activity and cell toxicity detection based on WST-8. WST-8 is a compound similar to MTT. In the presence of electron carriers, WST-8 can be reduced by dehydrogenase in mitochondria to produce water-soluble orange-yellow Formazan products. The amount of Formazan produced is proportional to the number of viable cells. The more cells proliferate, the faster and deeper the color becomes. By detecting the absorbance at 450 nm, the quantity of viable cells can be indirectly calculated. The detection sensitivity of Cell Counting Kit 8 is higher than that of other tetrazolium salts, such as MTT, XTT, or MTS.