An iridium complex-based probe for phosphorescent lifetime-elongated imaging of nitroreductase in living cells

Nitroreductase (NTR) is an important biomarker and often overexpressed in hypoxia tumors, thus the selective and precise detection of NTR is of great importance in the early diagnosis of tumors. Although various analytical methods have been constructed for NTR detection, there is still a lack of an effective photoluminescence probe for NTR using photoluminescence lifetime imaging (PLIM) within living cells. In this study, an iridium-based probe (Ir-NO2) decorated with p-nitrophenyl group has been designed and investigated for detection and imaging of NTR. Upon addition of NTR and nicotinamide adenine dinucleotide (NADH), the p-nitrophenyl group of Ir-NO2 underwent reduction and elimination, leading to generation of Ir-NH2. This transformation effectively blocked photoinduced electron transfer, resulting in an observable enhancement of phosphorescence intensity and an extension of phosphorescence lifetime during the detection process. The capability of Ir-NO2 to detect NTR at the cellular level was confirmed through PLIM analysis of hypoxia A549 cells.