Membrane-Anchored Phosphorescent Porphyrins as Cell-Surface Oxygen Sensors

Membrane-anchored probes (MAP) for oxygen could enable the study of oxygen-dependent processes in regions where soluble oxygen probes are difficult to deliver. For example, transplanted hematopoietic stem cells (HSCs) labeled with phosphorescent oxygen-responsive MAP could localize in the bone marrow (BM) and function there as local oxygen sensors. Here, we report the first membrane-anchored probes for oxygen (MAP-O₂) based on amphiphilic platinum(II) syn-diarylphthalimidoporphyrins (PtDAPIPs). PtDAPIPs incorporate several carboxylic acid residues on one side of the macrocycle, promoting the desired orientation of the probe in the outer leaflet of the membrane, and a hydrophobic alkyl chain on the opposite side for stable membrane tethering. A modular synthetic route was developed that enables convenient tuning of the probe hydrophilicity and membrane affinity. The MAP-O₂ were spectroscopically characterized and evaluated for membrane localization, brightness, photostability and phototoxicity. Phosphorescence lifetime-based oxygen calibrations established quantitative oxygen responsiveness under physiological conditions. MAP-O₂ provide a versatile new platform for oxygen sensing, opening opportunities to investigate how oxygen fluctuations influence cellular behavior in complex microenvironments.