EXPRESS: Cyclometalated Iridium Complex as Off-On-Off Reversible Photoluminescence Probe for Redox Cycle HSO 3 -/H 2 O 2 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)(2)Ir (5-chloro-1,10-phenanthroline) ([(4-pba)(2)Ir(5-Cl-phen)]PF6, probe 1), has been synthesized and applied to rapid, sensitive, and reversible detection and imaging of redox cycle HSO3 -/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 HSO3 - and H2O2 in aqueous solution within 1 min. The change of PL intensity is proportional to HSO3 - concentration from 40 mu M to 300 mu M and to H2O2 concentration from 40 mu M to 260 mu M. The detection limit is 10 mu M for HSO3 - and 20 mu M for H2O2. Additionally, probe 1 was applied to detect HSO3 - in food samples with satisfactory results. More importantly, PL imaging of HeLa cells indicates that probe 1 is able to image redox cycle HSO3 -/H2O2 in living cells.