Red fluorophore standard. Widely used in enzyme assay systems. Absorption and fluorescence of resorufin are pH dependent. Below the pKa (~6.0), Abs. shifts to ~ 480 nm and both E and fluorescence quantum yield are markedly lower. Resorufin is unstable in the presence of thiols such as dithiothreitol (DTT) and 2-mercaptoethanol.
Resorufin has high extinction coefficient and good chemical and photostability. These properties of resorufin make it perfect for its usage in inverse fluorescence assay to detect H2O2 by measuring the disappearance of its fluorescence upon horseradish peroxidase-mediated oxidation to a nonfluorescent derivative.