Nontoxic Dual-Function Probe for Ratiometric Oxygen Sensing and Cellular Imaging Based on Ir^III-Eu^III-Functionalized...

Hypoxia, characterized by low tissue oxygen concentration, is a common feature of diseases such as cardiac ischemia, inflammation, brain disorders, and solid tumors. Consequently, oxygen sensing has gained attention in diagnostics. In this study, we synthesized luminescent silica (SiO₂) particles functionalized with a bimetallic Ir^III-Eu^III complex for ratiometric oxygen sensing in biological media. Spherical SiO₂ particles (288 nm) were prepared via the sol-gel method to support and transport the water-insoluble luminescent complex. Then, the Ir^III-Eu^III complex was grafted stepwise, yielding the final hybrid SiO₂-Eu^IIIIr^III that exhibits a broad excitation band from 250 to 550 nm, yellow emission (by combining the green emission of Ir^III complex and red emission from Eu^III ion), and a negative surface potential in water, allowing stable suspension. Oxygen sensing experiments revealed a nonlinear sensing response with 70.5% sensitivity to oxygen concentration. Toxicity assays using Huh-7.5 cells showed no cytotoxicity in concentrations between 1.56 and 400 μg mL^-1. Confocal microscopy confirmed particles internalization, keeping their luminescent properties in the green and red regions, both emissions were detected separately after exciting at 488 nm. These results demonstrate the potential of SiO₂-Eu^IIIIr^III particles as a ratiometric luminescent probe for oxygen detection and cell labeling in biological applications.