Silver Nanoparticle-Assisted Photodynamic Therapy for Biofilm Eradication

As an antibiotic-free treatment, photodynamic therapy (PDT) is considered a promising alternative to antibiotic therapy for bacterial infections. However, the recalcitrant bacterial biofilm has manifested significant endurance to PDT, especially the gram-negative bacteria with the protective outer membrane. The ever-developing nanotechnology has provided new opportunities to overcome the biofilm infection. Here, we used silver nanoparticles as the auxiliary for PDT to implement a combined treatment against biofilms. A photosensitizer chlorin e6-modified polyethyleneimine was used as the ligands of silver nanoparticles. In the combined treatment, the silver and PDT exhibited a synergistic effect by mutually reinforcing each other. The surface plasma resonance of silver promotes the photodynamic effect to generate singlet oxygen, and the reactive oxygen can in turn stimulate the oxidative dissolution of the bactericidal Ag+. As a result, the combined treatment showed advanced antibacterial activity against both the Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Moreover, the Gram-negative E. coli, which is more susceptible to silver, becomes almost extinct even in the biofilm form. The therapy on mice with epidermal wound infection verified the high effectiveness of the nanocomposite. This research developed an efficient combined therapy for biofilm eradication, which strengthens the weakness of PDT in eliminating the Gram-negative bacteria, providing an alternative way to fight biofilm-related infections.