Purity >98% by HPLC. 10-acetyl-3,7-dihydroxyphenoxazin is a non-fluorescent, highly sensitive and stable probe for H2O2. It is an applicable as a fluorogenic substrate for peroxidase. In the presence of horseradish peroxidase (HRP), the reagent reacts in a 1:1 stechiometry with H2O2 to produce highly fluorescent resorufin. Because H2O2 is produced in many different enzymatic reactions, the reagent allows researchers to detect the activity of many different enzymes. 10-acetyl-3,7-dihydroxyphenoxazin has absorption and fluorescence emission maxima of approximately 563 nm and 587 nm, respectively, and because its extinction coefficient is high (54,000 cm-1M-1), the assay can be performed either fluorometrically or spectrophotometrically.