Iridium(III) Complex‐Based Activatable Probe for Phosphorescent/Time‐Gated Luminescent Sensing and Imaging of Cysteine in Mitochondria of Live Cells and Animals

This study reports an activatable iridium(III) complex probe for phosphorescence/time-gated luminescence detection of cysteine (Cys) in vitro and in vivo. The probe, [Ir(ppy)2 (NTY-bpy)](PF6 ) [ppy: 2-phenylpyridine; NTY-bpy: 4-methyl-4'-(2-nitrovinyl)-2,2'-bipyridine], is developed by incorporating a strong electron-withdrawing group, nitroolefin, into a bipyridine ligand of the IrIII complex. The luminescence of the probe is quenched owing to the intramolecular charge transfer (ICT) process, but switched on by a specific recognition reaction between the probe and Cys. [Ir(ppy)2 (NTY-bpy)](PF6 ) shows high sensitivity and selectivity for Cys detection and good biocompatibility. The long-lived emission of [Ir(ppy)2 (NTY-bpy)](PF6 ) allows time-gated luminescence analysis of Cys in cells and human sera. These properties make it convenient for the phosphorescence and time-gated luminescence imaging and flow cytometry analysis of Cys in live samples. The Cys images in cancer cells and inflamed macrophage cells reveal that [Ir(ppy)2 (NTY-bpy)](PF6 ) is distributed in mitochondria after cellular internalization. Visualizations and flow cytometry analysis of mitochondrial Cys levels and Cys-mediated redox activities of live cells are achieved. By using [Ir(ppy)2 (NTY-bpy)](PF6 ) as a probe, in vivo sensing and imaging of Cys in D. magna, zebrafish, and mice are then demonstrated.