A stable 10-Acetyl-3,7-dihydroxyphenoxazine (also called Ampliflu Red) liquid substrate reagent formulated for detecting horseradish peroxidase HRP activity, e.g. in ELISA. This reagent produces a highly fluorescent product (530/590nm) upon reaction with a peroxidase. The fluorescent product can also be visualized under a light source (510-550 nm). Procedure: 30 min. Size: 500 assays. Ship: on ice; Store: -20°C. Shelf life: 1 year.