Thermal effect of ir radiation at 1273 nm during direct photogeneration of singlet oxygen for solid tumors therapy

Increased reactivity makes singlet oxygen a cytotoxic agent. Infrared radiation at 1273 nm allows for direct photogeneration of singlet oxygen without the use of a photosensitizer. In this study, we demonstrated direct photogeneration of singlet oxygen in an aqueous environment using laser radiation at 1273 nm. Using chemical trapping methods, we determined the key parameters of generation, including the generation rate coefficient of singlet oxygen at an irradiance of1 mW/cm2 and a concentration of dissolved triplet oxygen of 1 μM: ξ=(4.3±0.1) • 10-8 ((s•mW/cm2)-1). We showed that irradiation of K562 and HeLa tumor cells with a focused laser beam at 1273 nm (diameter 100–1000 μm) leads to a significant cytotoxic effect in the irradiated area, not caused by thermal effects. We developed a mathematical model to calculate the photogenerated concentrations of singlet oxygen in an aqueous environment when irradiated with a 1273 nm laser. Based on experimental data, we calculated cumulative concentrations of singlet oxygen that result in cell death: 50% lethal dose for HeLa cells ~1000 μM, K562 cells ~3000 μM. Our research results confirm the potential application of 1273 nm laser radiation for direct photogeneration of singlet oxygen in tissues and the therapy of solid tumors