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 p conjugation of the cyaninemoiety. Dual fluorescence emissions are enhanced dramatically at λ(em) 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.