Antimicrobial photodynamic therapy using a diode laser with a potential new photosensitizer, indocyanine green‐loaded nanospheres, may be effective for the clearance of Porphyromonas gingivalis

Abstract

Antimicrobial photodynamic therapy (aPDT) is a new treatment method for the removal of infectious pathogens using a photosensitizer and light of a specific wavelength, e.g., toluidine blue with a wavelength of about 600nm. We explored a new photosensitizer and focused on indocyanine green (ICG), which has high absorption at a wavelength of 800-805nm. We investigated the bactericidal effect of PDT on Porphyromonas gingivalis using a new photosensitizer, ICG-loaded nanospheres with an 805nm wavelength low-level diode laser irradiation. We designed ICG-loaded nanospheres coated with chitosan (ICG-Nano/c) as a photosensitizer. A solution containing Porphyromonas gingivalis (10(8) CFU/mL) with or without ICG-Nano/c (or ICG) was prepared and irradiated with a diode laser or without laser irradiation as a negative control. The irradiation settings were 0.5W with a duty ratio of 10%, for 3-100ms in repeated pulse (RPT) or continuous wave mode. CFU were counted after 7d of anaerobic culture. We observed that ICG-Nano/c could adhere to the surface of P.gingivalis. When ICG-Nano/c was used for aPDT, irradiation with RPT 100ms mode gave the lowest increase in temperature. Laser irradiation with ICG-Nano/c significantly reduced the number of P.gingivalis (i.e., approximately 2-log10 bacterial killing). The greatest bactericidal effect was found in the RPT 100ms group. However, laser irradiation (RPT 100ms) with ICG, as well as without photosensitizer, had no effect on the number of bacteria. Within the limits of this study, ICG-Nano/c with low-level diode laser (0.5W; 805nm) irradiation showed an aPDT-like effect, which might be useful for a potential photodynamic periodontal therapy.