Single-chromophore-based ratiometric O₂ sensor for quantitative intracellular O₂ mapping

Accurate in-situ intracellular O₂ measurements are highly desired for the study of O₂-related physiology and pathology. Calibratable, ratiometric luminescent O₂-responsive probes, which are self-referenced, are ideal for such applications. The common strategy for designing such probes involves the conjugation of a fluorophore and a phosphorophore. However, this dual-chromophore approach often results in a large molecular size and high photobleaching susceptibility. Here we report a single-chromophore-based dual-emission Pt(II) complex named PtQTAC for O₂ sensing. PtQTAC has a simple structure and can be prepared with ease. Upon single excitation, PtQTAC simultaneously emits both fluorescence and phosphorescence, with well-separated spectra and balanced emission intensities. It shows a ratiometric response to O₂ levels, which fits the Stern-Volmer equation. When incorporated into nanoparticles, PtQTAC retains its O₂ sensitivity and could be readily taken up by cells. By detecting the signal from PtQTAC under a confocal microscope, intracellular O₂ concentrations can be precisely mapped and quantified after calibration. To the best of our knowledge, this is the first demonstration of intracellular O₂ concentration quantification using a single-chromophore-based luminescent probe.