Tailoring the optical properties of ZnO nano-layers and their effect on in vitro biocompatibility

Abstract

This paper highlights the use of Al₂O₃ and SnO₂ films as protecting layers to tailor the optical properties and biocompatibility of ZnO nano-films. ZnO, ZnO/Al₂O₃ and ZnO/SnO₂ nano-films have been deposited inside 3-dimensional (3D) structures such as anodic aluminium oxide (AAO) membranes via a gas phase atomic layer deposition (ALD) process. We show that ZnO/Al₂O₃ multilayers exhibit improved excitonic photoluminescence properties compared to ZnO only, whereas ZnO/SnO₂ multilayers quench the near band edge emission signal. In addition, in vitro experiments on Caco-2/TC7 cells and Vibrio fischeri bacteria reveal that ZnO/Al₂O₃ and ZnO/SnO₂ multilayers display enhanced biocompatibility in liquid media compared to ZnO. We attribute the improvement of the biocompatibility to a lower dissolution of the ZnO nano-film when protected by Al₂O₃ or SnO₂.