Laser ablation synthesis Au@NiO nanoparticles: a new frontier in broad-spectrum antibacterial nanomaterials.

The development of drug resistance has driven extensive efforts to create new antimicrobial nanomaterials capable of killing both Gram-negative and Gram-positive bacteria through different mechanisms. Here, we report the synthesis and antibacterial activity of Au, NiO, and core–shell Au@NiO nanoparticles (NPs), highlighting the synergistic interaction at the plasmonic metal/p-type semiconductor interface. The nanostructures were characterized physicochemically, and their antibacterial efficacy against Streptococcus mutans and Pseudomonas aeruginosa was tested using the agar well diffusion method. Quantitative data showed that Au@NiO NPs had the strongest antibacterial effect, with inhibition zones measuring 17.68 mm for S. mutans and 14.16 mm for P. aeruginosa larger than those of NiO NPs (13.39 mm and 11.10 mm) or Au NPs (10.95 mm and 9.85 mm), respectively. The mechanistic study indicates that the bactericidal activity is improved in two ways by the Au(core)–NiO(shell) structure: (1) the edge effect of the Au/NiO heterojunction promotes efficient separation and generation of ROS, and (2) the hydroxylated surface of the NiO shell encourages adhesion to bacterial cell membranes. This combined approach is especially effective at penetrating bacterial defenses, such as the thick peptidoglycan layer in Gram-positive bacteria and the lipopolysaccharide outer membrane in Gram-negative bacteria. These findings present a promising strategy for designing next-generation broad-spectrum antimicrobial nanostructures for use in biomedical coatings, oral care, and environmental disinfection.