Morphological impact of zinc oxide particles on the antibacterial activity and human epithelia toxicity.

ZnO nanoparticles are utilized in an ever growing number of products and can, therefore, be readily encountered in our everyday life. Human beings' outermost tissues consist of different epithelia and are, therefore, the most exposed to materials from the environment. In this paper, Caco-2 and Calu-3 cell lines were used, having been previously broadly applied for in vitro modelling of intestinal and respiratory epithelia, respectively. The toxicity of synthesized micro-, submicro- and nanoparticulate ZnO on these epithelia was measured and compared to the efficacy of the same ZnO particles as antibacterial agents. An approximately four-fold excess in antibacterial activity of ZnO nanoparticles over ZnO granulate was observed. The results of this paper reveal a sharp distinction between toxic nanoparticulate ZnO and safe ZnO particles of larger sizes in intestinal and airway in vitro epithelial models. In contrast, ZnO of larger particle sizes had only modestly lower antibacterial activity, which can be compensated for with higher dosing. These results show that nanoparticulate ZnO requires critical in vivo assessment before application.

Amino- and ionic liquid-functionalised nanocrystalline ZnO via silane anchoring - an antimicrobial synergy.

The synthesis of highly antimicrobial nanocrystalline zinc oxide and its covalent modifications are presented. In order to achieve further improvement of antimicrobial activity, the surface of ZnO was effectively modified with selected silanes comprising amino- and ionic liquid-functionalities. We demonstrate for the first time ionic liquid surface immobilization on ZnO and the application of this hybrid material for antimicrobial purposes. Different microscopic and spectroscopic techniques as well as size, surface and elemental composition analyses were employed to prove these modifications. Characterization revealed that surface and antimicrobial properties strongly depend on the modification employed. Most of the amino- and ionic liquid-functionalised nanocrystalline ZnO exhibited improved antimicrobial activity compared to commercially available silane-containing antimicrobial agents attached to nanocrystalline ZnO. Bacterial growth reduction was assessed by following the optical density of bacterial growth with different concentrations of the novel antimicrobial nanomaterials. Complete bacterial inactivation was achieved for specific amino- and ionic liquid-modifications at 0.125 g L-1, revealing the synergistic effect of ZnO and its modifications, exhibiting up to 2-fold improvement compared to unmodified ZnO.