Antibacterial Activity of Photocatalytic Metal Oxide Thin Films Deposited by Layer-by-Layer Self-Assembly

This paper reports the use of the Layer-by-Layer self-assembly (LbL) as an efficient technique for the fabrication of thin-films with antibacterial activity. The LbL coatings are composed of a positive polyelectrolyte such as Poly(allylamine hydrochloride) (PAH) and an anionic polyelectrolyte such as Poly(sodium 4-styrene sulfonate) solution (PSS). In addition, these polyelectrolytes can be also used as an adequate encapsulating agent of specific metal oxide precursors such as titanium dioxide (TiO₂) and iron oxide (Fe₂O₃) nanoparticles, making possible the fabrication of hybrid thin films composed of organic polymeric chains related to the polyelectrolytes and inorganic structure associated to the metal oxide nanoparticles. Four different LbL coatings have been fabricated and a comparative study about the resultant topographical, optical and wettability properties is presented by using light interferometry, atomic force microscopy (AFM), UV-Vis spectroscopy and water contact angle (WCA) measurements. In addition, X-ray fluorescence (XRF) has been also employed in order to corroborate the presence of metal oxide precursors inside the polymeric chains of the polyelectrolytes. Finally, the antibacterial tests have demonstrated that LbL coatings composed of metal oxide nanoparticles produce an enhancement in the efficacy and antibacterial activity.