Effect of microstructural changes in the biological behavior of magnetron sputtered ZnO thin films

This work is focused on the evaluation of the correlation between the microstructural changes of zinc oxide (ZnO) thin films and its biological behavior. For this study, ZnO thin films were prepared by reactive magnetron sputtering, using different deposition times and reactive gas (O₂) flows, and tested against a fungal pathogenic species, Candida albicans. Results showed that the increase of thickness of the films did not affect significantly the surface roughness but changed the crystalline structure of the films (ZnO in the hcp structure), which was followed by a small increase of antifungal properties, leading to a decrease of viable cells. The decrease of O₂ flow in the deposition chamber affected the roughness only slightly (roughly 1 nm difference between the different films) but resulted in a clear decrease in the crystallinity of thin films, which improved even further their antifungal activity. These results seem to indicate a correlation between structural features and the antifungal behavior of the ZnO thin films, which will be shown by different analyses. When tested against the fungal species, the films showed to be capable of reducing the growth rate and inhibit their growth, leading to a low number of microbial cells at the end of the experiment. A deeper analysis by flow cytometry on how the thin films affected the microbial cells showed a reduced global enzymatic activity in yeast cells after contact with the materials’ surface.