TMB is a non-toxic, non-mutagenic, colorless dye that is also used as a chromogenic agent in enzyme detection systems based on horseradish peroxidase (HRP). TMB can function as a photoacoustic probe for reactive oxygen and nitrogen species (ROS/RNS), reacting with hypochlorite, hydrogen peroxide, singlet oxygen, and nitrogen dioxide to produce blue oxidation products. TMB can detect the singlet oxygen produced by the outer membrane of Escherichia coli ATCC 25922.