Study of Photodegradation of Thiazion Dye Methylene Blue under Exposure to a Laser for Photodynamic Therapy

Purpose. To study the process of photodegradation of methylene blue under the influence of laser radiation with a wavelength of 660 nm, used for photodynamic therapy installations, for the formation of reactive oxygen species, in particular short-lived hydroxyl radicals, using electron paramagnetic resonance (EPR) spectroscopy.Methods. The residual concentration of methylene blue during photodegradation was determined using an HR2000 spectrometer. The formation of hydroxyl groups was detected using an EPR spectrometer SPINSCAN X.Results. Analysis of data on the photodegradation of methylene blue shows that under the influence of laser radiation with a wavelength of 660 nm, the structure of methylene blue is destroyed, manifested in the gradual discoloration of the dye solution. When trypaflavin is added to the solution, the rate of photodegradation of methylene blue slows down significantly. Analysis of ESR spectroscopy data shows that when methylene blue is exposed to a red laser, (OH’) radicals begin to intensively form in the solution. Their content increases significantly with increasing irradiation power.Conclusion. Irradiation of an aqueous solution of the thiazion dye methylene blue by a laser source with a power of 0.3÷1 W and a wavelength of 660 nm leads to its active photodegradation. The addition of trypaflavin leads to a slowdown in the process of photodegradation of methylene blue when irradiated with red light due to the consumption of part of the generated oxygen-containing radicals for the degradation of trypaflavin. According to EPR spectroscopy data using DMPO spin traps, it has been proven that when methylene blue is irradiated with a red laser, active formation of hydroxyl OH' radicals occurs. It was found that with increasing laser radiation intensity, the amount of generated hydroxyl radicals (OH') increases significantly. The presented results may contribute to the development of effective photosensitizers for photodynamic therapy of tumor tumors.