Biosensing, toxicity and stability of ZnO quantum dots – NanoZnOTox

The project is based on the engineering of diverse zinc oxide nanoparticles varying by their surface chemistry. These nanoparticles were characterized by microscopy and spectroscopy techniques. Their respective stability was evaluated by mass spectrometry, by measuring the emission of free Zn2+ ions using bacterial biosensors, or via methods combining dialysis spectrometry and plasma torch. The reactivity of the nanoparticles was studied by measuring the photo-induced generation of reactive oxygen species through specific colorimetric and/or fluorimetric assays. The overall toxicity of nanoparticles on bacterial cell was estimated from the alterations of growth kinetics, and the extinction of light emission in cells expressing a constitutive bioluminescence. The search for specific stresses caused by the nanoparticles was performed using bacterial fluorescent/luminescent biosensors, but also via transcriptomics (in progress). Direct damages caused by the nanoparticles were, for their part, investigated at the level of membranes proteins and DNA.

The results obtained in this project showed very different behaviors of ZnO QDs in terms of stability and toxicity depending on the concentration at which they were used and according to the dispersion medium. Used in water and at high concentrations, ZnO QDs are stable and producers of ROS. Photocatalytic applications, especially in the field of remediation / decontamination of wastewater is therefore possible for these nanomaterials. The photo-induced damage observed on DNA in the presence of ZnO QDs could also be valued. In contrast, when the QDs are dispersed at low concentrations in biological media, they decompose and release of Zn2+ ions which are then the only source of toxicity observed with the bacterial cells. In summary, although the accumulation of ZnO nanoparticles combined with exposure to light has little probability of occurring in the environment, additional effects caused by recurrent use and long term, or massive local expositions ( non-dispersed materials) can not be excluded and suggest great caution when using materials based on ZnO.

- Development of a simple, reproducible and extrapolated to large scale synthesis of ZnO nanocrystals via microfluidic processes. The developed method can be generalized to other metal oxide nanoparticles or semiconductor.
- Methodological development (proof of concept) for the evaluation of the toxicity of nanoparticles (and potentially all types of compounds / particles / radiation) by direct measurement of alterations caused by biological macromolecules without passing by in vivo tests. Communication actions on the subject in the scientific literature, scientific meetings, or meetings organized by the Competitiveness Cluster Hydreos are expected.
- Valuation of results in the generation and detection of ROS by ZnO nanoparticles for photocatalytic applications for the elimination of recalcitrant pollutants (drug residues) or bacterial decontamination as part of a new ANR project ( ANR PRUMOS, CD2I, 2013) as well as through a program of PHC UTIQUE collaboration with the University of Carthage (Tunisia).

From visible to white-light emission by siloxane-capped ZnO quantum dots upon interaction with thiols, A. Schejn, L. Balan, D. Piatkowski, S. Mackowski, J. Lulek, R. Schneider, Optical Materials, 2012, 34, 1357-1361.
One-pot non-injection route to CdS quantum dots via hydrothermal synthesis, A. Aboulaich, D. Billaud, M. Abyan, L. Balan, J.J. Gaumet, G. Medjahdi, J. Ghanbaja, R. Schneider, ACS Appl. Mater. Interfaces, 2012, 4, 2561-2569.
Physicochemical properties and cellular toxicity of (poly)aminoalkoxysilanes functionalized ZnO quantum dots, A. Aboulaich, C.-M. Tilmaciu, C. Merlin, C. Mercier, H. Guilloteau, G. Medjahdi, R. Schneider, Nanotechnology, 2012, 23, 335101 (9 pp).
Mass spectrometry techniques in the context of nanometrology, M. Fregnaux, J.J. Gaumet, S. Dalmasso, J.P. Laurenti, R. Schneider
Microelectronic Engineering, 2013, 108, 187-191.
Size-controlled synthesis of ZnO quantum dots in microreactors
A. Schejn, M. Frégnaux, J.-M. Commenge, L. Balan, L. Falk, R. Schneider, Nanotechnology, 2014, 25, 145606.
Atypical stress response to temperature and NaOCl exposure leading to septation defect during cell division in Cupriavidus metallidurans CH34, B. Arroua, X. Bellanger, H. Guilloteau, L. Mathieu, C. Merlin
FEMS Microbiology Letters, 2014, 353, 33–39.
Incidence of the core composition on the stability, the ROS production and the toxicity of CdSe quantum dots, F.-A. Kauffer, C. Merlin, L. Balan, R. Schneider, Journal of Hazardous Materials, 2014, 286, 246-255.
Aqueous synthesis and enhanced photocatalytic activity of ZnO/Fe2O3 heterostructures, F. Achouri, S. Corbel, A. Aboulaich, L. Balan, A. Ghrabi, M. Ben Said, R. Schneider, Journal of Chemistry and Physics of Solids, 2014, 75, 1081-1087.
Stability and toxicity of ZnO quantum dots: Interplay between nanoparticles and bacteria, X. Bellanger, P. Billard, R. Schneider, L. Balan, C. Merlin, Journal of Hazardous Materials, 2015, 283, 110–116.

In the past years, with the tremendous progresses made in the area of nanotechnologies and materials science, a huge diversity of engineered nanomaterials has been continuously elaborated. The uncertainty about the novel properties of these materials, which strongly depend on the particle size, shape and composition, and how that may relate to nanoscale operations at the biological level, has generated considerable concerns and could impact the implementation and acceptance of this new technology by the society.
The aim of this project is to characterize the toxicity associated to nanomaterials using ZnO quantum dots (QDs) as model. QDs are photoactive nanoparticles with a wide range of application ranging from photovoltaics to fluorescent bio-imaging. It has recently been demonstrated that QDs exhibited higher cytotoxicities than those of their components taken independently. This toxicity has at least two origins, a metal leakage from the core, and the production of reactive oxygen species (ROS), with a relative contribution of each that remains relatively difficult to evaluate. If the metal leakage is related to the composition and the stability of the nanoparticle, the ROS production is linked to its reactivity and its surface chemistry. With this project, we would like to set the basis of the relationship existing between the chemical structure, the stability and the toxicity of ZnO QDs.
The scientific program proposed is divided in three parts: (i) the design and engineering of 12 ZnO QDs and the evaluation of the relationships between the nanoparticles properties and their toxicological effects. Different surface ligands will be used in order to develop different kinds of interactions between the materials and the bacterial cells used as biological model. (ii), second, the evaluation of stability, both in the absence and in the presence of biomaterial, using original and innovative approaches including mass spectrometry and biosensing of Zn2+, and (iii) the evaluation of the QDs’ toxicity on bacteria using home made toxicity tests based on growth kinetics, the evaluation of cell membrane integrity and enzymatic activities after exposition to QDs, the evaluation of ROS-associated damages, and finally the use of a complete array bacterial stress response biosensors. In addition, the adaptability towards the newly engineered materials will be determined in order to evaluate the way bacteria could cope to newly engineered “anthropogenic pollutants”. Our work should allow to set the basis of an algorithm dedicated to the reliable prediction and assessment of the possible spectra of effects, from benefits to possible risks, and health hazards associated with exposure to nanomaterials as they become more widespread, pervasive agents in manufacturing and medicine.