Alamar blue is a reagent and accompanying assay used to quantify cellular metabolic
activity. Taken at a single time point, it can be used to determine the concentration of viable
cells in a sample. Taken at two or more time points of the same or similar samples, the assay
can be used to measure cell growth kinetics – the growth of a cell population over time.
The reagent solution contains the non-fluorescent blue-colored molecule resazurin,
which, when chemically reduced (a metabolic activity of cells), turns into the highly fluorescent
red-colored resorufin. Both the color change and the change in fluorescence allow for the direct
measurement of cell metabolic activity (and thus viable cell concentration) via absorbance or
fluorescence measurements in a plate reader.