Oxygen's pivotal role in biology extends to oncology, affecting photodynamic therapy, radiotherapy, and chemotherapy efficacy. While invasive oxygen electrodes are the standard for in vivo measurement, they lack cellular information and are limited to single point measurements. Alternatively, noninvasive optical oxygen probes, quenching in the presence of oxygen, offer fast spatially resolved insights. However, limited FDA approval restricts their clinical use. In this study, we explore the use of the endogenous molecule protoporphyrin IX (PpIX), to measure tissue oxygen, using a novel fluorescence imaging approach. Our goal is to calibrate the PpIX ratiometric signal for precise pO2 measurements. We demonstrate the correlation between PpIX ratiometric signal and tissue oxygen and present an estimated correlation curve. This advancement in non-invasive intracellular measurement holds profound implications across medical disciplines, and particularly for PDT.
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