Dihydrorhodamine 123

Dihydrorhodamine 123 (DHR 123) is a cell-permeable fluorogenic probe that is useful for the detection of reactive oxygen species (ROS) such as peroxide and peroxynitrite. It is not fluorescent until oxidized by ROS to the highly fluorescent product Rhodamine 123. Neither NO, superoxide, nor hydrogen peroxide alone appear to oxidize DHR, rather, these ROS are thought to combine with other cellular components such as cytochrome c oxidase or Fe²⁺ in order to oxidize DHR 123 to its fluorescent derivative Rhodamine 123. Formation of Rhodamine 123 can be monitored by fluorescence spectroscopy using excitation and emission wavelengths of 500 and 536 nm, respectively, or by absorbance spectroscopy at 500 nm (ε = 78,800 M^-1cm^-1).