Antibacterial activity of thin films TiO2 doped with Ag and Cu on Gracilicutes and Firmicutes bacteria

Dragomira Stoyanova,Todorka Vladkova,Iliana Ivanova,Orlin Angelov

doi:10.3897/biodiscovery.20.e21596

Abstract

This article aims to explore the antibacterial activity of thin films of TiO2 doped with Ag and Cu using two types of Gram-negative and Gram-positive test bacteria with clinical significance (Gracilicutes and Firmcutes bacteria). The thin films (thickness of about 60 nm) were deposited on glass substrates by radio frequency magnetron co-sputtering (r.f. power of 50 W) of TiO2 target with Ag and Cu pieces on its surface in an Ar atmosphere (0.8 Pa) without heating during the deposition. The total surface area of the Ag was 60 mm2 and that of the Cu was 100 mm2. Bacillus cereus, Staphylococcus epidermidis, Salmonella enterica, Escherichia coli and Pseudomonas sp. were used as test strains. The antibacterial actvity of the films was evaluated by the classical Koch's method and optical density measurements. The bactericidal effect was established at different time points between 30 min and 90 min for Pseudomonas sp. and S. enterica. The Firmicutes bacteria B. cereus and S. epidermidis were killed at the 4th and 8th hour of the treatment, respectively. The effect on E. coli was bacteriostatic until the 10th hour. The results were confirmed by assessment of the bacterial dehydrogenase activity. The studied thin films of TiO2 co-doped with Ag and Cu have a potential for application as antibacterial coatings.

Highlights

The antibacterial effect of the nanomaterials is due to different processes based on their surface biochemical functionality, partial dissolution of their components and mechanical antibacterial effect of their surface morphology
The result from the diffusion assay test have shown that the inhibition zone was different for the test bacteria: mm for E. coli and S. epidermidis, mm for B. cereus and 13-14 mm for Pseudomonas sp
The number of bacteria in a logarithmic scale sharply decreased at the 4th hour and the optical density dropped at the 3th hour from the beginning of the experiment, which determined the process of disinfection

Summary

Introduction

The antibacterial effect of the nanomaterials is due to different processes based on their surface biochemical functionality, partial dissolution of their components and mechanical antibacterial effect of their surface morphology. TiO2 is a widely used material for scientific studies and different applications in clinical practice due to its biocompatibility and high stability at chemical treatments and environmental conditions. The modification of the TiO2 band gap through doping with different chemical elements does not affect its ultraviolet light activity and increases the photocatalytic activity in sunlight. TiO2 nanoparticles (NPs) prepared by sol-gel technique were successfully applied for deactivation of different microorganisms (Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Staphylococcus aureus). Wong et al (2015) reported increasing the visible-light response and durability of silver nanoparticles impregnated in TiO2:(N) thin films against pathogens like E. coli, Streptococcus pyogenes, S. aureus and Acinetobacter baumanii A concentration dependence was established for the bacterial deactivation with Ag content in TiO2 thin films with a quantity of 1, 3, 5 and 7 μg/ml Bahadur et al (2016). Wong et al (2015) reported increasing the visible-light response and durability of silver nanoparticles impregnated in TiO2:(N) thin films against pathogens like E. coli, Streptococcus pyogenes, S. aureus and Acinetobacter baumanii

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