Synergistic interaction between wavelength of light and concentration of H₂O₂ in bactericidal activity of photolysis of H₂O₂

The present study aimed to evaluate the interaction between wavelength of light in the range of ultra violet A-visible and concentration of H₂O₂ in the reaction of photolysis of H₂O₂ from the point of view of hydroxyl radical (·OH) generation and the bactericidal activity. Light emitting diodes (LEDs) emitting the light at wavelengths of 365, 385, 400 and 465nm were used at an irradiance of 1000mW/cm². H₂O₂ was used at the final concentrations of 0, 250, 500, and 1000mM. Quantitative analysis of ·OH generated by the LED irradiation of H₂O₂ were performed using an electron spin resonance-spin trapping technique. In a bactericidal assay, a bacterial suspension of Staphylococcus aureus prepared in sterile physiological saline was irradiated with the LEDs. The bactericidal activity of each test condition was evaluated by viable counts. When H₂O₂ was irradiated with the LEDs, ·OH was generated and bacteria were killed dependently on the concentration of H₂O₂ and the wavelength of LED. The two-way analysis of variance revealed that the wavelength, the H₂O₂ concentration and their interaction significantly affected the yield of ·OH and the bactericidal activity of the photolysis of H₂O₂. Therefore, it is suggested that bactericidal activity of photolysis of H₂O₂ could be enhanced by controlling the wavelength and the concentration of H₂O₂, which may contributes to shortening the treatment time and/or to reducing the concentration of H₂O₂.