Antibacterial Activity of Visible Light Responsive-Silver-Nanoparticle/Titania Composite Thin Films with Unprecedently Higher Amounts of Silver

Abstract

To study the antibacterial efficacy of metallic Ag nanoparticle/titania (Ag-NP)/TiO₂ composite thin films against Escherichia coli (ATCC 25922), COMP-Ag_n with various amounts of Ag (10 mol% ≤ n ≤ 80 mol%) are fabricated on a quartz glass substrate at 600 °C using the molecular precursor method. The films are characterized by X-ray diffraction, X-ray photoelectron, scanning electron microscopy, transmission electron microscopy, photoluminescence, and UVvis techniques. The analysis reveals that the films are composed of metallic Ag-NPs embedded in a mixture of anatase and rutile matrix, with a volumetric fraction of Ag ranging from 0.18 to 0.68. The antibacterial activity of the TiO₂ thin film and COMP-Ag_n are determined by disk diffusion and viable cell count methods. Neither pure TiO₂ nor pure Ag films exhibit any discernible antibacterial under dark and visible light. The antibacterial of Ag content in composite films is observed to persist for a maximum increase of 70%. The model is proposed on the basis of photoexcited electron transfer from Ag NPs to the TiO₂ conduction band of COMP-Ag_n, which clarifies the main factors affecting the photoresponse and the excellent response to visible light via surface plasmon resonance.