EPR spectroscopy investigation of oxygen radical production by methylene blue and indocyanine green in aqueous solutions under laser irradiation in the context of antibacterial photodynamic therapy

Introduction: Antibacterial photodynamic therapy is a promising treatment modality in the anti-infective therapy of numerous oral diseases. It involves photo activation of a reactive substance (dye), thus releasing reactive oxygen species (ROS-radicals) which are highly destructive to the bacterial cell. However, thorough investigation of radical production properties of different dyes is not common in literature. Aim: The aim of this study was to investigate and evaluate oxygen radical-producing potential of two commonly used photoactive dyes in the context of antibacterial photodynamic therapy. Materials and methods: The radical-producing properties of two commonly used dyes for photodynamic therapy in oral medicine, methylene blue and indocyanine green, irradiated under laser irradiation are investigated using electron paramagnetic resonance (EPR) spectroscopy. The detection of reactive oxygen species is performed with “spin-trapping” technique. Results: The selected photoactive dyes showed promising yields of reactive oxygen species (ROS) in aqueous solutions. The comparative analysis of the results deemed methylene blue as the more productive photoactive agent. Conclusions: By employing the spin-trapping technique, this study indicates EPR-spectroscopy as a promising method of relative quantification of reactive oxygen species released by the photodynamic reaction in aqueous solutions.