Antimicrobial activity of flame-synthesized nano-TiO₂ coatings

Abstract

TiO2 in the form of nanocrystals possesses photocatalyst properties leading to excellent capability of\ud degrading a number of environmental contaminants such as organics, bacteria, and viruses. However, the\ud antimicrobial activity of nano-TiO2 coatings against different microorganisms is not yet well established.\ud Candida albicans, Aspergillus niger, Staphylococcus aureus and Streptococcus mutans are common nosocomial\ud and environmental pathogens responsible for biofilm-associated infections especially in indoor environments.\ud In this study, we produced thin coatings of TiO2 nanoparticles on aluminum substrates and\ud assessed whether they may prevent fungi and bacteria biofilm formation and whether this may be a synergistic\ud effect of TiO2 nanoparticles with UV irradiation, which is more representative of the natural conditions\ud for passive devices. Coatings of flame-synthesized nanoparticles were produced by direct\ud thermophoretic deposition on aluminum substrates through a rotating disk inserted in the flame. Particle\ud and coating characterization was performed by means of differential mobility analysis, Raman and X-ray\ud diffraction spectroscopy. Microbial biofilm formation on substrates with different TiO2 thicknesses were\ud evaluated by the colorimetric crystal violet method and quantified by spectrophotometry in four different\ud fungi and bacteria strains; the results were corroborated by scanning electron microscopy analysis. Substrates\ud with minimal TiO2 nanoparticle layers demonstrated a strong anti-biofilm effect against both fungi\ud and bacteria, due to the well-known cellular component photo-oxidation and to the enhanced nanomaterial\ud surface area. Interestingly, UV irradiation of the substrates at a low intensity for a short time demonstrated\ud a significant enhancement of the titania antimicrobial activity. TiO2 nanoparticle coatings may be\ud proposed as self-cleaning and self-disinfecting materials able to reduce microbial infections, especially in\ud indoor environments where hygiene is needed

Bacterial Biofilm Characterization and Microscopic Evaluation of the Antibacterial Properties of a Photocatalytic Coating Protecting Building Material

“…Even under very severe conditions of microbial contamination, the coating was still active and prevented the biofilm development on its surface. These results are also in accordance with a recent study that showed a significant antibacterial effect of TiO 2 coatings against the formation of microbial biofilms under low irradiance [40]. More tests would be required to validate the methodology.…”

“…The few studies that observed inactivation of microorganisms by photocatalysis with light intensities around 10 −3 W/m 2 showed much lower inactivation rates [49], confirming the major impact of light intensity on the process. Regarding the resistance to microbial biofilm, a recent study also showed significant efficiency of TiO 2 coatings against the development of microbial biofilms under relatively low irradiance (13 W/m 2 ) closer to real-world light intensity [40].…”

“…Furthermore, efficiencies of TiO 2 photocatalysis found in the literature are usually related to very high irradiances (>10 W/m 2 ) [28,29,39] that are far from the real-world conditions. Only recent studies have begun to investigate on the photocatalytic activity under low irradiances [40].…”

Structure and enhanced antimicrobial activity of mechanically activated nano TiO2

“…Taking into consideration that hydroxyl radicals usually cause oxidation of phospholipids within the membrane of microbial cells when the cells adhere to the surface of the TiO 2 catalyst, inducing thereby the loss of membrane integrity, it is expected that the samples TiO 2 ‐10 and TiO 2 ‐30 may show a major increase in the antimicrobial activity. It has also been reported that radicals not only act on TiO 2 surface, but also diffuse over short distances through the surrounding solution, consequently degrading organic compounds that are not in direct contact with the photocatalyst. However, as far as the dependence of the MIC on the activation time (Figure ) is concerned, it may be observed that the antimicrobial activity change rate is slightly lower (ie the degree of change in antimicrobial activity is lower) when activation time increases from 10 to 30 minutes than when it increases from 0 to 10 minutes.…”

“…Nanomaterials with exclusive photocatalytic properties may ensure adequate sanitation of environmentally contaminated surfaces and spaces, since nanoparticles can be used as self-consistent antimicrobial agents, in an aqueous suspension, or as coating layers for a common material surface. [1][2][3] Silver, ZnO and CuO nanoparticles have an important effect against microbial growth, but their utilization is restricted since they may pose a hazard to other organisms when they are released into the environment. 4 Reports on the application of TiO 2 as a photocatalyst in wastewater treatment, food industry, pharmacy, medicine, indoor environments and in development of new self-cleaning and antimicrobial materials, point out the advantages of utilization of this material due to its low cost and the fact that it does not pose a significant threat to the environment and human health.…”