Bromine indirubin FLIM/PLIM sensors to measure oxygen in normoxic and hypoxic PDT conditions

•Oxygen plays a crucial role in the effectiveness of PDT.•Sensors have been developed to observe oxygen consumption during PDT.•Bromine indirubin derivatives showed oxygen sensitivity within living cells. The induction of phototoxicity during photodynamic therapy (PDT) is dependent on oxygen availability. For this reason, the development of sensors to measure oxygen and oxygen consumption is extremely important. In this project we have used Fluorescence Lifetime imaging (FLIM) and Phosphorescence Lifetime Imaging/ delayed Fluorescence Lifetime Imaging (PLIM/dFLIM) to investigate the ability of bromine indirubin derivatives as oxygen sensors. The oxygen sensitivity of bromine indirubins was detected through PLIM/dFLIM. Moreover, we have observed, by measuring nicotinamide adenine dinucleotide (NADH) FLIM, that bromine indirubin has a significant impact on cellular metabolism by shifting the SCC-4 Cells metabolism from oxidative phosphorylation (OXPHOS) to glycolysis. In conclusion, this study successfully achieves its goals and provides important insights into the use of indirubin as a potential oxygen consumption sensor with the capability to identify and differentiate between normoxic and hypoxic regions within the cells.