Ir(III)-based Ratiometric Hypoxic Probe for Cell Imaging

Two new ratiometric hypoxia probes (Ir-C343 and Ir-GFP) are synthesized by covalently incorporating florescent internal standard molecules coumarin 343 (C343) and green fluorescent protein (GFP) into bis[1-(9,9-dimethyl-9 H -fluoren-2-yl)-isoquinoline] (succinylacetone) Ir(III) (Ir-fliq), respectively. After connecting with internal standard molecules, the Ir-fliq moiety still exhibits high sensitivity to oxygen concentration, while the fluorescence intensity of the internal standard remains relatively constant under different oxygen concentrations. As a result, a ratiometric response is realized that is only related to oxygen concentration. In addition, Ir-GFP shows more promising applications in the ratiometric hypoxia imaging of cells due to its long excitation wavelength, good water solubility, high biocompatibility, and low relative fluorescence intensity compared with the phosphorescent emitter Ir-fliq.