A novel fluorescent sensor for detection of highly reactive oxygen species, and for imaging such endogenous hROS in the mitochondria of living cells

A new dye, PTZ-Cy2, based on a hybrid cyanine–phenothiazine platform, is described. Oxidation by highly reactive oxygen species (hROS) involves attack at the thiazine sulfur atom and destruction of the π conjugation of the cyanine moiety. Dual fluorescence emissions are enhanced dramatically at λem 470 nm and 595 nm, and PTZ-Cy2 thus serves both as an absorbance ratiometric and a fluorescent "off–on" sensor for detecting hROS. Moreover PTZ-Cy2 shows selectivity for hROS over other oxidants, and gives a highly sensitive response to such endogenous species within the mitochondria of living cells.