Biocompatible Ir(III) Complexes as Oxygen Sensors for Phosphorescence Lifetime Imaging

Area of Science:

• Organometallic Chemistry
• Bioimaging
• Biocompatible Materials

Background:

• Developing biocompatible near-infrared (NIR) phosphorescent complexes for bioimaging and oxygen sensing in live systems remains a challenge.
• Existing probes often face limitations in solubility, biocompatibility, and environmental stability.

Purpose of the Study:

• To design and synthesize novel iridium complexes with enhanced aqueous solubility and biocompatibility for use as NIR phosphorescent probes.
• To evaluate their potential as triplet oxygen sensors in biological systems.

Main Methods:

• Synthesis and full characterization of four novel iridium [Ir(N^C)2(N^N)]+ complexes using NMR spectroscopy and ESI mass spectrometry.
• Evaluation of photophysical properties including excitation, NIR emission (730 nm), and quantum yields in aqueous media.
• Assessment of biocompatibility, toxicity, stability (pH, serum, concentration), and oxygen sensing capabilities using phosphorescence lifetime imaging in cell cultures.

Main Results:

• The synthesized iridium complexes exhibit NIR emission at 730 nm with quantum yields up to 12% in water, with excitation near the biological window of transparency.
• Complexes with enhanced shielding demonstrated low toxicity, excellent bleaching stability, and independence from pH, serum, and concentration variations.
• Phosphorescence lifetime imaging revealed a distinct response to oxygen variations (2.0-2.3 μs under normoxia, 2.8-3.0 μs under hypoxia), correlating with calibration data.

Conclusions:

• The designed iridium complexes are highly soluble, biocompatible, and stable NIR emitters suitable for bioimaging.
• These complexes function effectively as semi-quantitative oxygen sensors in biological environments, showing significant phosphorescence lifetime changes under varying oxygen levels.