Mitochondria and Lysosome‐Targeted Luminescent Iridium(III) Probe for Selective Detection of Hg ² ⁺ in Aqueous Media and Living Cells

Mercury is one of the most toxic environmental elements and poses significant health risks to humans and other animals. Therefore, the selective detection of mercury in environmental and biological settings is of critical importance. This study presents an iridium(III) complex probe (Ir1), constructed with two cyclometalating 2-phenylquinoline ligands and an N,N-donor 2,2'-bipyridine-4,4'-diboronic acid as the ancillary ligand for "turn-off" luminescent sensing of Hg²⁺ ions. The boronic acid groups, strategically incorporated into the bipyridine ligand, serve as the reaction sites, enabling a rapid and selective transmetalation with Hg²⁺, resulting in decreased luminescence. Ir1 shows a detection limit of 26.5 µM toward Hg²⁺ in aqueous media over a wide pH range (4-9) and retains selectivity in the presence of competing metal ions. Confocal fluorescence microscopy confirmed that Ir1 accumulates predominantly in the mitochondria and lysosomes of living cells, where it exhibits Hg²⁺-dependent luminescence quenching. This organelle-specific targeting is particularly relevant due to mercury's high affinity for thiol-rich proteins in these compartments, making Ir1 a valuable tool for intracellular mercury monitoring.