Photophysical properties of methylene blue in aqueous solution sprayed onto biological surfaces

The paper presents a set of experiments revealing photophysical processes associated with methylene blue assisted photodynamic inactivation of pathogens on different surfaces, both inorganic (glass) and organic (superficial fascial flaps of chicken and fish and mushroom cap peel). The experiments were performed in normoxic and hyperoxic conditions. The characteristic times of singlet oxygen generation and degradation on the surfaces were evaluated from the analysis of time-resolved signals of singlet oxygen phosphorescence. The photobleaching kinetics of methylene blue on the surfaces were found to be significantly different and dependant on solution oxygenation. The characteristic decay times varied from dozens of seconds for glass to dozens of minutes for fascial flaps and mushroom peel. The interpretation of the experimental results obtained was done on the basis of a set of master equations describing photosensitizer-assisted singlet oxygen generation and photosensitizer photobleaching. The results obtained on methylene blue photodynamics and conclusions made were compared with results of similar experiments performed earlier with Radachlorin photosensitizer.