Phosphorescence based O₂ sensors – Essential tools for monitoring cell and tissue oxygenation and its impact on metabolism

Oxygenation condition at the cellular level is a critical factor in tissue physiology and common pathophysiological states including cancer, metabolic disorders, ischemia-reperfusion injury and inflammation. O₂ and ROS signalling and hypoxia research are rapidly growing areas spanning life and biomedical sciences, but still many current cell and tissue models and experimental set ups lack physiological relevance, particularly precise control of cellular O₂. Quenched-phosphorescence O₂ sensing enables implementation of such in situ control of cellular O₂ and the creation of physiological conditions in respiring samples analysed in vitro. The advantages of optical O₂ sensing are the non-invasive, contactless, real-time, quantitative monitoring of O₂ concentration, which can be performed in the gas or liquid phase, macroscopically or microscopically, by point measurement or in imaging mode, with sub-cellular spatial resolution, in a flexible manner and with various cell and tissue models. Significantly, this same technology can also be used to probe the metabolism of cells and tissue under specific oxygenation conditions and their responses to changing conditions. Here we describe the range of available O₂ sensing systems and tools, their analytical capabilities, uses in cell/tissue physiology and hypoxia research, and strategies for integration in routine experimental procedures.