The Abnormal Physicochemical Phenomena of Singlet Oxygen Sensor Green in Water in the Presence of Ultrasound

The detection of Singlet oxygen (¹O₂) is of great interest to develop cancer therapies, because it can initiate a plethora of events that result in cell death. Singlet oxygen sensor green (SOSG) is considered the preferred probe because of its claimed high selectivity to Singlet oxygen (¹O₂). Although many researchers have used SOSG to detect ¹O₂ generation in Sonodynamic therapy (SDT) processes, the effect of ultrasound irradiation on SOSG has not been comprehensively evaluated. In this study, we conducted systematic experiments to determine SOSG activation in the presence of ultrasound irradiation. We found that the SOSG exhibited the abnormal physicochemical phenomena in distilled water in the presence of ultrasound. The fluorescence intensity of SOSG increased significantly when exposed to ultrasound alone. The results showed that there was a linear positive correlation between the treatment duration of different ultrasound intensities or SOSG concentrations and the fluorescence intensity of SOSG, respectively. In addition, scavenger tests also indicated that hydroxyl radicals (•OH) might be involved in the activation of SOSG. In conclusion, our results suggest that the influences of experimental conditions to SOSG must be fully considered, and that SOSG may not be a suitable probe for ¹O₂ in SDT.