Photocatalytic Nanocomposite\nBased on Titanate Nanotubes\nDecorated with Plasmonic Nanoparticles for Enhanced Broad-Spectrum\nAntibacterial Activity

Infections resulting from microorganisms pose an ongoing\nglobal\npublic health challenge, necessitating the constant development of\nnovel antimicrobial approaches. Utilizing photocatalytic materials\nto generate reactive oxygen species (ROS) presents an appealing strategy\nfor combating microbial threats. In alignment with this perspective,\nsodium titanate nanotubes were prepared by scalable hydrothermal method\nusing TiO<sub>2</sub> and NaOH. Ag, Au, and Ag/Au-modified titanate\nnanotubes (TNTs) were prepared by a cost-effective and simple ion-exchange\nmethod. All samples were characterized by XRD, FT-IR, HRTEM, and DLS\ntechniques. HRTEM images indicated that the tubular structure was\npreserved in all TNTs even after the replacement of Na<sup>+</sup> with Ag<sup>+</sup> and/or Au<sup>3+</sup> ions. The antibacterial\nactivity in dark and sunlight conditions was evaluated using different\nbacterial strains, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The results showed that while\na low bacterial count (∼log 5 cells per well) was used for\ninoculation, the TNTs exhibited no antibacterial activity against\nthe three bacterial strains, regardless of whether they were tested\nunder light or dark conditions. However, the plasmonic nanoparticle-decorated\nTNTs showed remarkable activity in the dark. Additionally, Ag/Au-TNTs\ndemonstrated significantly higher activity in the dark compared with\neither Ag-TNTs or Au-TNTs alone. Notably, under dark conditions, the\nAu/Ag-TNTs achieved log reductions of up to 4.5 for P. aeruginosa, 5 for S. aureus, and 3.7 for E. coli. However, when\nexposed to sunlight, Au/Ag-TNTs resulted in a complete reduction (log\nreduction ∼9) for P. aeruginosa and E. coli. The combination of two\nplasmonic nanoparticles (Ag/Au) decorated on the surface of TNTs showed\nsynergetic bactericidal activity under both dark and light conditions.\n Ag/Au-TNTs could be explored to design surfaces that are responsive\nto visible light and exhibit antimicrobial properties.