Fluorescein is a fluorophore widely used in microscopy, forensics and serology to detect latent blood stains. Fluorescein has an absorption maximum at 490 nm and emission maximum of 514 nm (in water). It has a pKa at 6.4 and multiple ionization equilibria. This leads to pH dependent absorption and emission over the range of 5 to 9. It has an isoabsorptive point at 460 nm.