Mitochondria-targeted phosphorescent probes for Cu²⁺/H₂S bioimaging and H₂S dynamics monitoring in hepatic...

Cu²⁺ and H₂S participate in vital physiological activities, especially mitochondrial function. Endogenous H₂S has served as a critical biomarker of liver injury. Accordingly, detecting Cu²⁺ and H₂S in mitochondria, as well as monitoring H₂S fluctuations in living cells and intact organisms (especially in the liver), is of great significance for elucidating their mitochondrial physiological roles and evaluating the progression of liver-related disorders.

Herein, two mitochondria-targeted phosphorescent probes (Ir and its Cu²⁺ complex Ir-Cu) were rationally designed for mitochondrial and in vivo sensing of Cu²⁺ and H₂S via a metal displacement strategy. Each probe integrates a lipophilic cationic cyclometalated Ir(III) luminophore with mitochondrial targeting capability and a cyclen unit for specific Cu²⁺ recognition. The system undergoes distinct "on-off" and "off-on" phosphorescence switching at 580 nm and 630 nm upon sequential addition of Cu²⁺ and H₂S. The as-prepared probes possess superior properties including an ultra-large Stokes shift (>200 nm), long lifetime (800 ns), rapid response (Cu²⁺: 5 min; H₂S: 10 s) and high selectivity. They were successfully utilized for imaging Cu²⁺ and H₂S in mitochondria and model organisms such as zebrafish, mice and Arabidopsis thaliana. In particular, Ir-Cu achieved visualization of H₂S fluctuations in LPS-induced cells, liver tissues of hepatic inflammatory mice, and serum from normal and diseased mice.

The developed mitochondria-targeted phosphorescent probes achieve in vitro and in vivo imaging of Cu²⁺ and H₂S. Distinct from conventional organic fluorophores, these Ir(III) complexes (Ir and Ir-Cu) can effectively eliminate false-positive signals and enhance spatial resolution, exhibiting great promise for studying biological processes and mitochondria-related liver injury.