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.