Gold nanoparticles (AuNPs) synthesized via laser ablation serve as photosensitizers for the photodynamic inactivation of <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i> bacteria

Bacterial infections pose a serious problem, often necessitating the use of antimicrobials in substantial quantities. Furthermore, microbial resistance has significantly escalated alongside the rapid adaptation of bacteria to antimicrobial agents. This research aims to explore alternative solutions for diminishing Staphylococcus aureus and Pseudomonas aeruginosa bacteria through photodynamic therapy. Gold nanoparticles (AuNPs) were synthesized using a laser ablation technique and applied as photosensitizers at concentrations of 10.0, 15.0, and 21.5 μg/mL. A 405 nm blue diode laser was employed for photodynamic inactivation (PDI) against Staphylococcus aureus and Pseudomonas aeruginosa . Antibacterial efficacy was evaluated by quantifying bacterial reduction through Total Plate Count (TPC) in CFU/mL and confirmed using the disc diffusion assay. The research results indicated that adding 21.5 µg/mL of AuNPs photosensitizer at a volume of 50 µL led to a notable reduction in bacterial colonies. The most effective reduction in Staphylococcus aureus colonies was achieved with 150 s of laser exposure at an energy level of 2.87 J/cm 2 , reducing (80.3± 5.39)%. Similarly, the optimal reduction in Pseudomonas aeruginosa colonies occurred with 180 s of laser exposure at an energy level of 3.44 J/cm 2 , reducing (78.70±4.50)%. Blue laser irradiation at 405 nm combined with 21.5 μg/mL AuNPs effectively reduced Staphylococcus aureus by (80.37 ± 5.39)% in 150 s and Pseudomonas aeruginosa by (78.70 ± 4.50)% in 180 s, demonstrating its potential as an alternative antibacterial therapy.