A strategy for monitoring oxygen concentration, oxygen consumption, and generation of singlet oxygen using a phosphorescent photosensitizer

Abstract

Monitoring oxygen concentration ([O2]), oxygen consumption, and generation of singlet oxygen (1O2) is critical in photodynamic therapy (PDT) used for the precise treatment of cancer. To this end, a strategy based on a phosphorescent photosensitizer, gadolinium-hematoporphyrin monomethyl ether (Gd-HMME), was developed for monitoring [O2] in this study. Diphenylisobenzofuran (DPBF) was used to consume 1O2 produced by the Gd-HMME-mediated PDT. A sealed system comprising Gd-HMME and DPBF under irradiation was designed to simulate PDT when tissue oxygen was insufficient. Upon irradiation by a 532-nm laser, Gd-HMME phosphorescence initially increased rapidly, reached a maximum, and remained unchanged thereafter, because oxygen in the system was exhausted. The increase in phosphorescence increased with increasing fluence rates, suggesting that the change in phosphorescence was related to oxygen consumption. The depletion of DPBF in the system indicated the generation of 1O2 and a reaction between DPBF and 1O2. The phosphorescence decreased rapidly when the system was re-exposed to air. In contrast, the change in the phosphorescence intensity in an open cuvette was minimal and could be neglected. Thus, [O2] and generation of 1O2 in PDT could be monitored using the phosphorescence intensity of the photosensitizer, based on the dependence of phosphorescence and singlet oxygen quantum yield on [O2].