Antimicrobial effects of rose red upconversion nanoparticles (UCNPs-RB) based photodynamic therapy on Enterococcus faecalis infection

INTRODUCTION: Enterococcus faecalis (E. faecalis) is a predominant pathogen associated with persistent endodontic infections due to its resistance to conventional disinfectants and ability to form robust biofilms. This study aimed to evaluate the antibacterial efficacy and biocompatibility of a novel near-infrared (NIR)-activated photosensitizer, Rose Bengal-conjugated upconversion nanoparticles (UCNP-RB), against E. faecalis both in vitro and in vivo. METHODS: UCNP-RB nanocomposites were synthesized and characterized using transmission electron microscopy (TEM) and spectral analysis. Reactive oxygen species (ROS) generation under 808 nm NIR irradiation was quantified using the 1,3-diphenylisobenzofuran (DPBF) probe. Cytotoxicity was assessed in human dental pulp cells (hDPCs) via the Cell Counting Kit-8 (CCK-8) assay. In vitro antibacterial efficacy against planktonic E. faecalis and 14-day mature biofilms was evaluated at a concentration of 100 µg/mL using colony-forming unit (CFU) counts, adenosine triphosphate (ATP) bioluminescence, and scanning electron microscopy (SEM). Additionally, a murine model of apical periodontitis was established to assess the in vivo therapeutic efficacy of UCNP-RB-mediated antimicrobial photodynamic therapy (aPDT) compared to 1% sodium hypochlorite (NaClO) irrigation, with outcomes measured by micro-computed tomography (micro-CT). RESULTS: The synthesized UCNP-RB nanocomposite successfully converted near-infrared (NIR) light into visible emission, triggering efficient reactive oxygen species (ROS) generation. An optimal concentration of 100 µg/mL was identified for subsequent experiments. UCNP-RB-mediated aPDT demonstrated potent antibacterial efficacy, achieving a > 99% reduction in planktonic E. faecalis and approximately 90% inhibition of mature biofilm viability (p < 0.05). In vivo, micro-CT analysis revealed that the UCNP-RB aPDT group exhibited a 67% reduction in periapical bone defect volume compared to the untreated control group, indicating significant promotion of periapical healing. CONCLUSIONS: The UCNP-RB nanocomposites synthesized in this study exhibited uniform morphology and potent photodynamic activity. At an optimal concentration of 100 µg/mL, the system demonstrated significant antibacterial efficacy against E. faecalis both in vitro and in vivo, highlighting its potential as an effective agent for endodontic disinfection.