Kinetic analysis of singlet oxygen generation in a living cell using Singlet Oxygen Sensor Green

Singlet oxygen (¹O₂) can be generated in a living cell upon focused laser irradiation of an intracellular photosensitizer. In this study, ¹O₂ generation from the plasma membrane-targeted protoporphyrin IX (PpIX) in human nasopharyngeal carcinoma CNE2 cells was monitored indirectly by using the fluorescence probe Singlet Oxygen Sensor Green agent (SOSG). The confocal images indicate that the fluorescence of SOSG in the vicinity of the cells that incubated with PpIX was dramatically enhanced with the increased irradiation time, while there is no significant enhancement for the control cells. Moreover, the fluorescence of SOSG is dramatically enhanced with the increase of the intracellular PpIX in CNE2 cells for the same photoirradiation time. These observations imply that the ¹O ₂ generated from the plasma membrane-targeted PpIX in the CNE2 cells can be escaped into the extracellular medium and to react with the SOSG to produce SOSG-EP, and the fluorescence enhancement of SOSG around the cells mainly depends on the intracellular PpIX. Our findings may be useful for further monitored the ¹O₂ that can be escaping from the living cells.