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 TiO 2 (UCNPs@TiO 2 ), and (2) investigate its inhibitory effects via antibacterial photodynamic therapy (aPDT) against periodontitis-related pathogens. Methods The core β-NaYF 4 :Yb 3+ ,Tm 3+ were synthesized via thermal decomposition and further modified with the TiO 2 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@TiO 2 had an average diameter of 39.7   nm. UCNPs@TiO 2 nanoparticles had positively charged (+12.4   mV) surface and were biocompatible and non-cytotoxic. Under the excitation of NIR light (980   nm), the core NaYF 4 :Yb 3+ ,Tm 3+ UCNPs could emit intense ultraviolet (UV) light, which further triggered the aPDT function of the shell TiO 2 via energy transfer, thereby realizing the remarkable antibacterial effects against planktons and biofilms of periodontitis-associated pathogens. NIR-triggered UCNPs@TiO 2 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@TiO 2 -based aPDT against the three species was ranked to be: S. sanguinis   <   F. nucleatum   =   P. gingivalis . Metabolic activities of biofilms were also greatly reduced via NIR-triggered aPDT (p   <   0.05). Significance Upconversion fluorescence-based aPDT achieved strong inhibiting effects against all three species of periodontitis-related pathogens. This novel nanotechnology demonstrated a high promise to inhibit periodontitis, with exciting potential to combat other oral infectious diseases such as deep endodontic infections.