Quantitative monitoring of the level of singlet oxygen using luminescence spectra of phosphorescent photosensitizer

The lack of accurate and robust photodynamic therapy dosimetry is one of the obstacles for the widespread clinical applications. In this study, we propose a methodology to monitor the production of reactive oxygen species in real-time using the phosphorescent spectra of metalloporphyrin based photosensitizer. The correlation among the phosphorescence intensity, the ¹O₂ quantum yield (Φ_Δ) and the oxygen concentration [O₂] was established. A method of determining Φ_Δ with different [O₂] was studied based on comparative spectrophotometry, and the quantum yield Φ_Δ of gadolinium metalated hematoporphyrin mono ether (Gd-HMME) in methanol was determined for different [O₂]. With our method, both [O₂] and Φ_Δ could be monitored simultaneously using the phosphorescence spectra. The photochemical reactions in a liquid phantom composed of Gd-HMME and ¹O₂ capture 1,3-diphenylisobenzofuran (DPBF) were correlated using the kinetics equations of singlet oxygen generation and reaction. Using our method, the ¹O₂ quantum yield becomes observable and the ¹O₂ dose rate could be calculated by the product of photosensitizer absorption and its ¹O₂ quantum yield. Moreover, this ¹O₂ dosimetry could be observed by spectral imaging intuitively without complex analysis, and is especially suitable for precise customized photodynamic treatment.