Ag-Decorated Titania\nNanoparticles for Antibacterial\nApplications

In this work, titania nanoparticles\n(TiO<sub>2</sub>NPs) and silver\nnanoparticles (AgNPs) were combined in situ to obtain a single TiO<sub>2</sub>–Ag nanoplatform with synergistic antibacterial effects\nand perspectives in biological applications. To improve colloidal\nstability in the aqueous environment, the bifunctional (3-mercaptopropyl)trimethoxysilane\n(MPTMS) and sodium 3-mercapto-1-propanesulfonate (3MPS) were used\nas stabilizing agents for covalent binding to TiO<sub>2</sub>NP (formation\nof Ti–O–Si chemical bonds) and AgNP surfaces (through\nthe Ag–S bond), respectively. Synthesis conditions were optimized\nby tuning the Ag content decorating the TiO<sub>2</sub>NPs, and the\ncolloidal stability, size, morphology, and chemical composition were\nstudied in both solution and solid-state by UV–visible, Fourier-transform\ninfrared, <sup>1</sup>H NMR, X-ray photoelectron spectroscopy, field\nemission scanning electron microscopy-energy-dispersive X-ray spectroscopy,\ntransmission electron microscopy, inductively coupled plasma optical\nemission spectrometry, dynamic light scattering, and ζ-potential.\nThe antibacterial activities of these nanohybrids were investigated\non Gram-positive and Gram-negative bacteria, and the results showed\nan enhanced antibacterial effect arising from the combination of TiO<sub>2</sub>NPs and AgNPs in the nanohybrid with the lower Ag content\n(more than 60% in the case of S. aureus exposed to TiO<sub>2</sub>–Ag), compared to the pristine\nTiO<sub>2</sub>NPs and control groups. Electron paramagnetic resonance\nwith spin trapping detected the presence of hydroxyl radicals both\nin the nanohybrids and in the pristine TiO<sub>2</sub>NPs, supporting\nthe hypothesis that the antibacterial effect is related to the presence\nof reactive oxygen species. The results of this research contribute\nto the synthesis of new potent antimicrobial nanohybrids for applications\nin more complex biological media.