How can cell viability assays be classified?

Cell viability assays can be classified as: dye exclusion assays, fluorometric assays, luminometric assays, colorimetric assays, and flow cytometric assays. Dye exclusion assays are used to determine the number of viable cells present in a cell suspension. Examples include trypan blue, eosin, and congo red exclusion assays. Fluorometric assays are widely used for the determination of the kinetic mechanisms of enzyme reactions. A fluorometric assay occurs with the formation of a fluorescent product from a non fluorescent substrate or vice versa. Colorimetric assays use a colorimeter to determine concentration of a chemical compound in a solution by measuring spectral absorbance of a compound at a specific wavelength. A color is generated during the reaction of a detection chemical with the target substance. Flow cytometry rapidly analyzes single cells or particles as they flow past a laser beam, while suspended in a buffered salt solution. Prominent flow cytometric assays include membrane permeability, membrane asymmetry, and mitochondrial assays. A luminometric assay is a type of assay that measures light emission generated during a specific chemical reaction. It involves the use of luminescent enzymes or molecules that create light as a result of their interaction with a substrate. A common luminometric assay is the luciferase assay.