A fast and selective two-photon phosphorescent probe for the imaging of nitric oxide in mitochondria

Nitric oxide (NO) is a vitally important cellular messenger molecule related to numerous physiological events and diseases. It is more than 10 years now that mitochondria are suspected to be sources of nitric oxide. Hence, mitochondrial NO tracking probes play an indispensable role in NO behavior analysis. However, a majority of previously reported NO probes can only be employed under one-photon microscopy, often with several drawbacks during application. In the present study, an iridium(III) complex containing 1,10-phenanthroline-5,6-diamine (Ir-Mito-NO) was synthesized and determined to possess high specificity to NO in mitochondria, low cytotoxicity, and rapid and specific "off-on" two-photon phosphorescence. Thus, this complex was developed to image mitochondrial NO levels in living cells, 3D multicellular spheroids and zebrafish.