Lucigenin is a chemiluminescent probe used to detect superoxide production and the presence of chloride. It can be used to detect superoxide production by enzymatic and cellular sources. It is a sensitive method that has been applied to the monitoring of superoxide production from xanthine oxidase, microsomal NADPH cytochrome reductase, and NADPH oxidases of phagocytes, endothelial cells, fibroblasts, and smooth muscle cells of blood vessel walls. However, it produces similar chemiluminescence signals in isolated aortic and cardiac tissues from wild-type and Nox1-Nox2-Nox4 triple knockout mice, suggesting that it is not selective for NADPH-based ROS production. It also reacts with hydrogen peroxide without generating free radical intermediates and has been used to detect lipid hydroperoxide in oils. Lucigenin is also used as a fluorescent chloride-sensitive indicator, with its fluorescence being quenched by chloride (ex/em = 455/505 nm, respectively). Lucigenin fluorescence is insensitive to phosphate, sulfate, and nitrate.
In the case of lucigenin it is first reduced to a cation radical. Then it reacts in its univalently reduced form with ROS to produce dioxetane, which breaks down to generate photons. These probes cannot measure the individual free radicals but measure global ROS levels in the sample. Luminescence signals are expressed in relative light units (RLU), a direct measure of free radicals produced.
