Mechanism of Photodamage of Microbial Cells Sensitized by Indotricarbocyanine Dye

The mechanism of photodamage of E. coli Gram-negative bacterial cells sensitized with indotricarbocyanine dye PK220 was studied upon exposure to radiation from an LED source with emission spectrum maximum wavelength λ_max = 745 nm corresponding to the long-wavelength absorption band of the dye. The intensity of the cells' own (not enhanced by activator additives) light-induced chemiluminescence was used to assess the magnitude of the photobiological effect. The main contribution to their photodestruction immediately after cessation of cell-suspension irradiation came from singlet oxygen and to a lesser extent from H₂O₂. Hydroxyl radicals did not play a significant role in the mechanism of sensitized photochemical processes.