What is the principle of alamar Blue assay?

The alamar Blue assay uses a nontoxic, cell-permeable dye, resazurin, which serves as a REDOX indicator dye. The alamar Blue assay relies on the conversion of the initially weakly fluorescent blue dye resazurin to a highly fluorescent pink compound called resorufin in response to cellular metabolic activity. The intensity of the pink fluorescence is directly linked to the quantity of viable cells, providing a direct measure of cell health.