Novel nanotechnology and near-infrared photodynamic therapy to kill periodontitis-related biofilm pathogens and protect the periodontium

Objective. Periodontal tissue destruction and tooth loss are increasingly a worldwide problem as the population ages. Periodontitis is caused by bacterial infection and biofilm plaque buildup. Therefore, the objectives of this study were to: (1) develop a near-infrared light (NIR)-triggered core-shell nanostructure of upconversion nanoparticles and TiO2 (UCNPs@TiO2), and (2) investigate its inhibitory effects via antibacterial photodynamic therapy (aPDT) against periodontitis-related pathogens. Methods. The core beta-NaYF4:Yb3+,Tm3+ were synthesized via thermal decomposition and further modified with the TiO2 shell via a hydrothermal method. The core-shell structure and the upconversion fluorescence-induced aPDT treatment via 980 nm laser were studied. Three periodontitis-related pathogens Streptococcus sanguinis (S. sanguinis), Porphyromonas gingivalis (P. gingivalis) and Fusobacterium nucleatum (F. nucleatum) were investigated. The killing activity against planktonic bacteria was detected by a time-kill assay. Single species 4-day biofilms on dentin were tested by live/dead staining, colony-forming units (CFU), and metabolic activity. Results. The hexagonal shaped UCNPs@TiO2 had an average diameter of 39.7 nm. UCNPs@TiO2 nanoparticles had positively charged (+12.4 mV) surface and were biocompatible and non-cytotoxic. Under the excitation of NIR light (980 nm), the core NaYF4:Yb3+,Tm3+ UCNPs could emit intense ultraviolet (UV) light, which further triggered the aPDT function of the shell TiO2 via energy transfer, thereby realizing the remarkable antibacterial effects against planktons and biofilms of periodontitis-associated pathogens. NIR-triggered UCNPs@TiO2 achieved much greater reduction in biofilms than control (p < 0.05). Biofilm CFU was reduced by 3-4 orders of magnitude via NIR-triggered aPDT, which is significantly greater than that of negative control and commercial aPDT control groups. The killing efficacy of UCNPs@TiO2-based aPDT against the three species was ranked to be: S. sanguinis