Surface-Modified Zinc Oxide Nanoparticles for Antialgal and Antiyeast Applications

We explored the factors and mechanisms of the antiyeast and antialgal effect of zinc oxide nanoparticles (ZnONPs) coated with zinc sulfide (ZnS), silica (SiO2), poly(sodium 4-styrenesulfonate) sodium salt (PSS), and poly(allylamine hydrochloride) (PAH) polyelectrolytes. We examined the activity of various concentrations of bare and surface modified ZnONPs toward microalgae (C. reinhardtii) and yeast (S. cerevisiae) cells upon illumination with UV light compared with that under visible light and in dark conditions to evaluate the impact of the oxidative stress due to the reactive oxygen species (ROS). We also prepared ZnS-coated ZnONPs, SiO2-coated ZnONPs, and combinations of polyelectrolyte (PSS and PAH)-coated ZnONPs and examined their antiyeast and antialgal effects. The nanoparticles of the anionic surface (ZnONPs/ZnS, ZnONPs/SiO2, and ZnONPs/PSS) showed much lower antialgal and antiyeast activity than the ones with a cationic surface functionality (ZnONPs/PSS/PAH and bare ZnONPs). The effect of the ZnONPs surface coating was found to be much stronger than the ROS effect due to illumination with UV light. This indicates that the nanoparticles attachment to the microbial cell wall is much more important for their antimicrobial action than the ROS generation alone. This could be explained by the poor adhesion of ZnONPs/ZnS, ZnONPs/SiO2, and ZnONPs/PSS to the cells due to electrostatic repulsion. In contrast, the particle–cell electrostatic adhesion in the case of cationic ZnONPs/PSS/PAH and bare ZnONPs led to enhanced antiyeast and antialgal action. This study brings important insights about the role of the ZnONPs surface coatings on their nanotoxicity and antimicrobial action and could potentially lead to the development of better antibiofouling coatings and antiyeast formulations.