Test Principle: MTT is 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide which can be reduced by some dehydrogenases in mitochondria to form a crystalline dark purple product formazan. Formazan can be completely dissolved by DMSO and its absorbance is near 570 nm wavelength. The more and faster the cells proliferate, the darker the color is, and the more cytotoxic, the lighter the color is. For the same cells, there is a linear relationship between the depth darkness of color and the number of cells.