Chitosan-coated gold nanostars with photothermal activity for enhanced disinfection efficacy of sodium hypochlorite in antibacterial-based root canal therapy

Enterococcus faecalis can persist in root canal isthmuses and accessory canals despite conventional irrigation with sodium hypochlorite (NaOCl). Although high concentrations of NaOCl are effective, they pose safety risks. Therefore, strategies to enhance the efficacy of low-concentration NaOCl are clinically desirable. This study aimed to evaluate whether coating gold nanostars (AuNS) with chitosan (CS) to form a nanohybrid (AuNS-CS) can enhance the antibacterial efficacy of low-concentration NaOCl under low-power laser irradiation. The synthesis and comprehensive analysis of AuNS-CS nanohybrids were completed. Root canal models inoculated with E. faecalis were prepared. The antibacterial and antibiofilm capabilities of NaOCl (0.1–2.5%) alone or in combination with AuNS-CS and 810 nm diode laser irradiation (500 mW, 1 min), were evaluated using a colony-forming unit (CFU)·mL− 1 assay. Real-time temperature monitoring was performed. This nanohybrid enables efficient temperature elevation in NaOCl with low power laser irradiation (500 mW). AuNS-CS alone or under irradiation showed negligible antibacterial activity. NaOCl (0.1–2.5%) alone reduced planktonic E. faecalis viability by 1.74–3.71 log10 CFU·mL− 1 (p < 0.0001). The addition of AuNS-CS with 810 nm diode laser further reduced bacterial viability by 6 log10 CFU·mL− 1 (p < 0.0001), achieving complete eradication. In biofilm models, AuNS-CS combined with NaOCl (0.1–2.5%) under 810 nm diode laser irradiation reduced by 1.92–5.58 log10 CFU·mL− 1 (p < 0.0001). NaOCl (0.1–2.5%) alone resulted in a reduction of 0.16–3.68 log10 CFU·mL− 1, which was significantly lower than the combined treatment. The AuNS-CS nanohybrid enhances the antibacterial activity of low-concentration NaOCl under low-power laser irradiation, overcoming the limitations of conventional NaOCl treatment. This approach offers a promising strategy for more effective root canal disinfection and supports further exploration of nanoparticle-assisted endodontic therapies.