Eradication of planktonic bacteria by shape-tailored gold nanoparticle photothermia†

Bacterial antimicrobial resistance (AMR) has emerged as a global challenge, exacerbated by the formation of biofilms. To address this issue, the bactericidal effect of gold nanoparticle photothermia has been explored. Gold nanoparticles with different morphologies: spherical (AuNSP), rods (AuNRO), stars (AuNST), and flower-shaped (AuNFL) were synthesised and characterised. Scanning and transmission electron microscopy images confirm the morphologies and give dimensions for the different types of nanoparticles in good agreement with those from dynamic light scattering measurements. Their photothermal capacities under irradiation at 808 and 1064 nm were assessed. The specific absorption rates were determined, and light-to-heat conversion efficiencies evaluated in the heating and cooling phases. Phothermally induced localized hyperthermia significantly increased the mortality rate of planktonic Escherichia coli in the stationary phase, approaching 100% for AuNRO, AuNST, and AuNFL, while AuNSP was ineffective. This demonstrates that bactericidal efficacy is highly dependent on nanoparticle morphology. These findings highlight the potential of shape-tailored gold nanoparticles for developing effective antibacterial treatments.