Antimicrobial Activity of TiO 2 Coatings Prepared by Direct Thermophoretic Deposition of Flame-Synthesized Nanoparticles
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Antimicrobial Activity of TiO2 Coatings Prepared by Direct Thermophoretic Deposition of Flame-Synthesized Nanoparticles Gianluigi De Falco1,2, Amalia Porta3, Pasquale Del Gaudio3, Mario Commodo1, Patrizia Minutolo1 and Andrea D’Anna2 1
Istituto di Ricerche sulla Combustione, CNR, Piazzale Vincenzo Tecchio 80, 80125, Napoli, Italy
2
Dipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli Federico II, Piazzale Vincenzo Tecchio 80, 80125, Napoli, Italy
3
Dipartimento di Farmacia, Università degli Studi di Salerno, Via Giovanni Paolo II 132, 84084, Fisciano (Salerno), Italy ABSTRACT This study reports the development of a one-step method for the production of antimicrobial protective coatings for aluminum surfaces with titania nanoparticles. An aerosol flame synthesis system was used to produce monodisperse, ultra-fine TiO2 nanoparticles, which were directly deposited by thermophoresis onto plates of aluminum alloy by means of a rotating disc. Fuel-lean reactor conditions were used to synthesize pure anatase nanoparticles of 3.5 nm in diameter. Substrates were mounted onto the rotating disc that repetitively passes through the flame. Convection due to the rotational motion cooled the substrates, on which particles were deposited as films by thermophoresis. Such a system allowed to obtain submicron coatings of different thickness, by varying the total time of deposition. The antimicrobial activity of TiO2 coatings was tested against the Gram positive bacterium Staphylococcus aureus. To determine the inhibition of biofilms formation, microbes were plated on TiO2 coatings and a semiquantitative colorimetric assay was performed using crystal violet. The tests showed that the TiO2 coating obtained with tdes=10 s inhibits up to 70-80% Staphylococcus aureus biofilm formation, and the inhibition of biofilms formation was confirmed by means of Scanning Electron Microscopy observation. Also, the antimicrobial properties of the coatings was enhanced by irradiating the samples in the UV region. The results of the present work are promising for using titania films as protective coatings for applications where an antimicrobial activity is required. INTRODUCTION The degradation of the air quality in any crowded indoor environment is often due to the presence of microbial populations, which are responsible for the spreading of different diseases [1]. Several studies have shown that different microorganisms are able to grow on both indoor and outdoor building materials [2], such as Aspergillus niger and Candida albicans, which are common indoor fungi, as well as Staphyloccoccus aureus and Streptococcus mutans, which can be found in nosocomial environment. Those types of microorganisms are able to form biofilms on walls, air duct surfaces and plants, and this phenomenon is strictly related to their pathogenicity and environmental colonization [3]. Nanomaterials can be used as new and more effective sainting agents for environmentally contaminated surfaces [4]. Titanium dioxi
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