Aug 21, 2012
Silanization protects ZnO quantum dots from dissolution
Nanosized inorganic metal oxides, and zinc oxide in particular, exhibit unique physical and chemical properties, and are of interest to developers. For example, nano-ZnO has many applications including catalysis, gas sensing, piezoelectronics, UV-shielding and bio-imaging. The traditional view is that zinc oxide is non-toxic, but numerous studies have already demonstrated that nano-ZnO particles are toxic to mammalian, fungal and bacterial cells. The toxicity of nano-ZnO may originate from the particle dissolution and Zn2+ leakage and/or oxidative damage due to the production of reactive oxygen species, but the relative contribution of these two mechanisms remains uncertain.
Recently, researchers in France have conducted an innovative study that focuses on the influence of ZnO quantum dot (QD) surface ligands on cytotoxicity towards Escherichia coli bacterial cells. The nanocrystalline particles were synthesized through a sol-gel process and further functionalized with (poly)aminotrimethoxysilanes so that the dots could be dispersed in water. TEM and XRD analysis showed that the ZnO QDs had a diameter of 4 nm and possessed a hexagonal wurtzite structure.
Cytotoxicity studies showed that while QD concentrations of 5 mM caused a complete growth arrest of E. coli, aminosiloxanes-capped QDs were only weakly toxic at lower doses (0.5 or 1 mM).
The biosensor bacteria Cupriavidus metallidurans AE1433 was used to evaluate the concentrations of bioavailable Zn2+ ions leaked from the QDs. Biosensor measurements revealed that the concentration of Zn2+ was too low to explain the inhibitory effects of ZnO QDs and that the siloxane shell prevents ZnO QDs from dissolving in aqueous environments, contrary to uncapped ZnO nanoparticles. Based on the results, oxidative stress may be the dominant toxicity mechanism for ZnO QDs and the scientists make recommendations on the next steps to follow.
The study successfully links the physicochemical properties and the antibacterial activity of ZnO QDs and should provide guidance for manufacturing of safe and environmentally benign nanomaterials.
More details can be found in the journal Nanotechnology.
About the author
The study was performed jointly by research teams working at the Université de Lorraine, France. Abdelhay Aboulaich and Carmen-Mihaela Tilmaciu are postdoctoral researchers from the Reactions and Chemical Engineering Laboratory (LRGP). Christophe Merlin is an associate professor in microbiology and a research scientist at the Laboratory of Physical Chemistry and Microbiology (LCPME). Cédric Mercier is a postdoctoral researcher at the Jean Lamour Institute (IJL). Hélène Guilloteau and Ghouti Medjahdi are research assistants at LCPME and IJL, respectively. Raphaël Schneider is professor of organic chemistry and research scientist at LRGP. This work was supported by the Agence Nationale pour la Recherche (ANR CESA 2011, project NanoZnOTox).