Cyclometalated Iridium Complex as Off-On-Off Reversible Photoluminescence Probe for Redox Cycle /H₂O₂ in Living Cells

The development of new methods for the detection of redox cycle is important for biological and clinical diagnoses. Here, a new cyclometalated iridium complex, (4-(2-pyridyl) benzaldehyde)₂Ir (5-chloro-1,10-phenanthroline) ([(4-pba)₂Ir(5-Cl-phen)]PF₆, probe 1), has been synthesized and applied to rapid, sensitive, and reversible detection and imaging of redox cycle $$/H₂O₂ in living cells. The probe 1 is synthesized by using 4-(2-pyridyl) benzaldehyde as main ligand and 5-chloro-1,10-phenanthroline as ancillary ligand. Probe 1 exhibited "off-on-off" photoluminescence (PL) signal change in response to $$ and H₂O₂ in aqueous solution within 1 min. The change of PL intensity is proportional to $$ concentration from 40 μM to 300 μM and to H₂O₂ concentration from 40 μM to 260 μM. The detection limit is 10 μM for $$ and 20 μM for H₂O₂. Additionally, probe 1 was applied to detect $$ in food samples with satisfactory results. More importantly, PL imaging of HeLa cells indicates that probe 1 is able to image redox cycle $$/H₂O₂ in living cells.