What dyes are used in flow cytometry for cell viability testing?

Dyes used in flow cytometry for cell viability testing can be classified into categories:

1) Fixable viability dyes (e.g. Cell Meter™ fixable cell stains) that can react with amines on cellular proteins. They are a large family of cell-impermeable fluorescent viability dyes that are optimized to match the major excitation lasers of common flow cytometers, such as 350, 405, 488, 633 and 647 nm. These dyes are impermeant to live cells, so only cell surface proteins are available to react with dyes, resulting in dim staining. Dead cells, however, with a compromised membrane, are more readily react with these dyes, exhibiting much brighter staining than the live cells.

2) Nonfixable viability dyes that can be classic cell-impermeable DNA binding dyes (e.g. Propidium iodide), esterase substrates (e.g. calcein-AM), or a combination of both.