Antibacterial activity of tin-doped zinc oxide thin films deposited by laser ablation

Abstract

The main purpose of this research is to assess the potential of doped zinc oxide (ZnO)-based materials in providing antibacterial activity to bioinert implants. Thus, the current study deals with the production and characterization of tin (Sn)-doped ZnO thin films grown by the pulsed laser deposition (PLD) technique. The coprecipitation method was applied for the synthesis of the primary powders, that were subsequently converted into targets. The latter were employed in several deposition experiments, for which the substrate temperature (room temperature and 400 °C) and oxygen pressure (100 and 700 mTorr) were varied in order to elucidate the influence of the processing parameters on the functional properties. Next, the paper covers a full examination of the compositional, structural, optical, and morphological features of ZnO intermediate or final samples. Moreover, the thin films were characterized in terms of antibacterial activity against Escherichia coli (E. coli) gram-negative bacterium, and biocompatibility in the presence of mouse fibroblast cells. The results revealed a finer morphology for the doped target sintered at 1200 °C, consisting of grains several micrometers in size and a large proportion of interconnected pores, as well as the partial integration of Sn in the crystal lattice of ZnO, the rest of the dopant being trapped in a Sn-rich secondary phase (Zn2SnO4). The morphological assessment of the layers obtained by laser ablation revealed the pronounced effect of substrate temperature on the processes of nucleation and crystal growth, namely the occurrence of a denser packing of grains with significant higher dimension. Moreover, a higher oxygen pressure during deposition promoted an increased roughness for the deposited samples. The best antibacterial performance was achieved in the case of Sn-doped samples deposited at 400 °C, which demonstrates the beneficial contribution of the dopant ions.