Photocatalytic antibacterial activity of nano-TiO2 (anatase)-based thin films: Effects on Escherichia coli cells and fatty acids

•Thin films consisting of small TiO2 nanoparticles were prepared using sol–gel method.•The antibacterial efficiency in sunlight mimicking conditions were evaluated.•The antibacterial effects of the films were linked to bacterial cell membrane damages.•XPS was used to study the decomposition of fatty acids during photocatalysis.•XPS data indicates chemical changes to the fatty acid structure during photocatalysis.

Titanium dioxide is a photocatalyst with well-known ability to oxidise a wide range of organic contaminants as well as to destroy microbial cells. In the present work TiO2 nanoparticles with high specific surface area (150 m2/g) were used to prepare nanostructured films. The TiO2 nanoparticle-based film in combination with UV-A illumination with intensity (22 W/m2) comparable to that of the sunlight in the UV-A region was used to demonstrate light-induced antibacterial effects. Fast and effective inactivation of Escherichia coli cells on the prepared thin films was observed. Visualization of bacterial cells under scanning electron microscopy (SEM) showed enlargement of the cells, distortion of cellular membrane and possible leakage of cytoplasm after 10 min of exposure to photoactivated TiO2. According to the plate counts there were no viable cells as early as after 20 min of exposure to UV-A activated TiO2. In parallel to effects on bacterial cell viability and morphology, changes in saturated and unsaturated fatty acids – important components of bacterial cell membrane-were studied. Fast decomposition of saturated fatty acids and changes in chemical structure of unsaturated fatty acids were detected. Thus, we suggest that peroxidation and decomposition of membrane fatty acids could be one of the factors contributing to the morphological changes of bacteria observed under SEM, and ultimately, cell death.

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