Vers des quantum dots moins toxiques, une approche "safer by design"

Quantum dots (QDs) are fluorescent semiconductor nanocrystals with exceptional optical properties, which make them particularly attractive in optoelectronic fields and for biomedical applications. However, during their life cycle, the aging of QDs can lead to the degradation of these compounds, inducing the release of toxic elements. Even if toxicity studies on indium-based QDs are still limited, they show a lower intrinsic toxicity in comparison to the heavy metal containing Cd-based QDs. In this context, our laboratory synthetizes different InP QDs with different shell designs, following a safer by design approach, with the aim of producing less toxic QDs with better optical properties. These QDs are composed of a InZnP/Zn(Se,S) core/shell structure which is covered or not by a thick or a thin additional ZnS layer. In this study, primary human keratinocytes which come from breast surgeries, were exposed to these QDs, either pristine or after simulating environmental weathering. First, the physico-chemical transformations of QDs during aging are characterized. Significant photophysical and structural modifications are highlighted and transformation products are identified. However, the results show that these physico-chemical transformations are slowed down by the presence of a double shell, especially when it is thick. Then, the evaluation of QDs toxicity are performed and new assays are developed via high content screening (HCS) on an automated microscope. While pristine QDs were relatively stable and not very toxic to cells, it was not true for their degradation products. Exposure of cells to aged QDs demonstrated high toxicity at low concentrations and modifyed the expression of some genes and proteins essential for cellular homeostasis. These results show that new generations of QDs are safer. However, it’s important to keep improving their photostability since their dissolution and the release of toxic elements at the end of their life are still inevitable.Les quantum dots (QD) sont des nanocristaux semi-conducteurs fluorescents aux propriétés optiques exceptionnelles, ce qui les rend particulièrement attractifs dans les domaines de l’optoélectronique et pour les applications biomédicales. Cependant, au cours de leur cycle de vie, le vieillissement des QDs peut conduire à la dégradation de ces composés, induisant la libération d'éléments toxiques. Même si les études de toxicité sur les QDs à base d'indium sont peu nombreuses, certaines révèlent une toxicité intrinsèque plus faible que les QDs contenant des métaux lourds comme le Cd. Dans ce contexte, notre laboratoire synthétise différents QDs d’InP recouverts de coquilles, conçus par une approche « safer by design », dans le but de produire des QDs moins toxiques avec de meilleures propriétés optiques. Ces QDs sont constitués d'une structure cœur/coquille de InZnP/Zn (Se,S) qui est recouverte, ou non, d'une couche additionnelle de ZnS, épaisse ou mince. Dans cette étude, des kératinocytes primaires humains, issus de chirurgies mammaires, sont exposés aux QDs, après synthèse ou après vieillissement environnemental simulé. Dans un premier temps, les transformations physico-chimiques des QDs au cours du vieillissement sont caractérisées et mettent en évidence d’importantes modifications photophysiques et structurales ainsi que la formation de produits de transformation. Néanmoins, les résultats montrent que les transformations physico-chimiques des QDs sont ralenties par la présence de la double coquille, notamment lorsqu’elle est épaisse. Dans un second temps, l’évaluation de la toxicité des QDs est effectuée et de nouveaux tests sont dévelopés en criblage à haut contenu (HCS) sur un microscope automatisé. Alors que les QDs non vieillis se sont révélés relativement stables et peu toxiques pour les cellules, il n’en fût pas de même pour leurs produits de dégradation. L’exposition des cellules aux QDs vieillis a mis en évidence une forte toxicité à faibles concentrations, modifiant l’expression de certains gènes et protéines essentiels à l’homéostasie cellulaire. Ces résultats montrent que les nouvelles générations de QDs sont plus sûres. Cependant, il est important de continuer à améliorer leur photostabilité puisque leur dissolution et le relargage d’éléments toxiques en fin de vie sont inévitables pour le moment

Towards less toxic quantum dots, a safer by design approach

Les quantum dots (QD) sont des nanocristaux semi-conducteurs fluorescents aux propriétés optiques exceptionnelles, ce qui les rend particulièrement attractifs dans les domaines de l’optoélectronique et pour les applications biomédicales. Cependant, au cours de leur cycle de vie, le vieillissement des QDs peut conduire à la dégradation de ces composés, induisant la libération d'éléments toxiques. Même si les études de toxicité sur les QDs à base d'indium sont peu nombreuses, certaines révèlent une toxicité intrinsèque plus faible que les QDs contenant des métaux lourds comme le Cd. Dans ce contexte, notre laboratoire synthétise différents QDs d’InP recouverts de coquilles, conçus par une approche « safer by design », dans le but de produire des QDs moins toxiques avec de meilleures propriétés optiques. Ces QDs sont constitués d'une structure cœur/coquille de InZnP/Zn (Se,S) qui est recouverte, ou non, d'une couche additionnelle de ZnS, épaisse ou mince. Dans cette étude, des kératinocytes primaires humains, issus de chirurgies mammaires, sont exposés aux QDs, après synthèse ou après vieillissement environnemental simulé. Dans un premier temps, les transformations physico-chimiques des QDs au cours du vieillissement sont caractérisées et mettent en évidence d’importantes modifications photophysiques et structurales ainsi que la formation de produits de transformation. Néanmoins, les résultats montrent que les transformations physico-chimiques des QDs sont ralenties par la présence de la double coquille, notamment lorsqu’elle est épaisse. Dans un second temps, l’évaluation de la toxicité des QDs est effectuée et de nouveaux tests sont dévelopés en criblage à haut contenu (HCS) sur un microscope automatisé. Alors que les QDs non vieillis se sont révélés relativement stables et peu toxiques pour les cellules, il n’en fût pas de même pour leurs produits de dégradation. L’exposition des cellules aux QDs vieillis a mis en évidence une forte toxicité à faibles concentrations, modifiant l’expression de certains gènes et protéines essentiels à l’homéostasie cellulaire. Ces résultats montrent que les nouvelles générations de QDs sont plus sûres. Cependant, il est important de continuer à améliorer leur photostabilité puisque leur dissolution et le relargage d’éléments toxiques en fin de vie sont inévitables pour le moment.Quantum dots (QDs) are fluorescent semiconductor nanocrystals with exceptional optical properties, which make them particularly attractive in optoelectronic fields and for biomedical applications. However, during their life cycle, the aging of QDs can lead to the degradation of these compounds, inducing the release of toxic elements. Even if toxicity studies on indium-based QDs are still limited, they show a lower intrinsic toxicity in comparison to the heavy metal containing Cd-based QDs. In this context, our laboratory synthetizes different InP QDs with different shell designs, following a safer by design approach, with the aim of producing less toxic QDs with better optical properties. These QDs are composed of a InZnP/Zn(Se,S) core/shell structure which is covered or not by a thick or a thin additional ZnS layer. In this study, primary human keratinocytes which come from breast surgeries, were exposed to these QDs, either pristine or after simulating environmental weathering. First, the physico-chemical transformations of QDs during aging are characterized. Significant photophysical and structural modifications are highlighted and transformation products are identified. However, the results show that these physico-chemical transformations are slowed down by the presence of a double shell, especially when it is thick. Then, the evaluation of QDs toxicity are performed and new assays are developed via high content screening (HCS) on an automated microscope. While pristine QDs were relatively stable and not very toxic to cells, it was not true for their degradation products. Exposure of cells to aged QDs demonstrated high toxicity at low concentrations and modifyed the expression of some genes and proteins essential for cellular homeostasis. These results show that new generations of QDs are safer. However, it’s important to keep improving their photostability since their dissolution and the release of toxic elements at the end of their life are still inevitable

Réseaux de femmes, femmes en réseaux (XVIe-XXIe siècles)

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Evaluation of the Dermal Toxicity of InZnP Quantum Dots Before and After Accelerated Weathering: Toward a Safer-By-Design Strategy

International audienceQuantum dots (QDs) are colloidal fluorescent semiconductor nanocrystals with exceptional optical properties. Their widespread use, particularly in light-emitting diodes (LEDs), displays, and photovoltaics, is questioning their potential toxicity. The most widely used QDs are CdSe and CdTe QDs, but due to the toxicity of cadmium (Cd), their use in electrical and electronic equipment is now restricted in the European Union through the Restriction of hazardous substances in electrical and electronic equipment (RoHS) directive. This has prompted the development of safer alternatives to Cd-based QDs; among them, InP QDs are the most promising ones. We recently developed RoHS-compliant QDs with an alloyed core composed of InZnP coated with a Zn(Se,S) gradient shell, which was further coated with an additional ZnS shell to protect the QDs from oxidative surface degradation. In this study, the toxicity of single-shelled InZnP/Zn(Se,S) core/gradient shell and of double-shelled InZnP/Zn(Se,S)/ZnS core/shell/shell QDs was evaluated both in their pristine form and after aging in a climatic chamber, mimicking a realistic environmental weathering. We show that both pristine and aged QDs, whatever their composition, accumulate in the cytoplasm of human primary keratinocytes where they form agglomerates at the vicinity of the nucleus. Pristine QDs do not show overt toxicity to cells, while aged QDs show cytotoxicity and genotoxicity and significantly modulate the mRNA expression of proteins involved in zinc homeostasis, cell redox response, and inflammation. While the three aged QDs show similar toxicity, the toxicity of pristine gradient-shell QD is higher than that of pristine double-shell QD, confirming that adding a second shell is a promising safer-by-design strategy. Taken together, these results suggest that end-of-life degradation products from InP-based QDs are detrimental to skin cells in case of accidental exposure and that the mechanisms driving this effect are oxidative stress, inflammation, and disturbance of cell metal homeostasis, particularly Zn homeostasis. Further efforts to promote safer-by-design formulations of QDs, for instance by reducing the In and Zn content and/or implementing a more robust outer shell, are therefore warranted

Physico-Chemical Transformation and Toxicity of Multi-Shell InP Quantum Dots under Simulated Sunlight Irradiation, in an Environmentally Realistic Scenario

International audienceQuantum dots (QDs) are widely used in optoelectronics, lighting, and photovoltaics leadingto their potential release into the environment. The most promising alternative to the highly toxiccadmium selenide (CdSe) QDs are indium phosphide (InP) QDs, which show reduced toxicity andcomparable optical and electronic properties. QD degradation leads to the release of toxic metal ionsinto the environment. Coating the QD core with robust shell(s) composed of another semi-conductormaterial enhances their properties and protects the QD from degradation. We recently developeddouble-shelled InP QDs, which proved to be less toxic than single-shell QDs. In the present study,we confirm their reduced cytotoxicity, with an LC50 at 77 nM for pristine gradient shell QDs and>100 nM for pristine thin and thick shell QDs. We also confirm that these three QDs, when exposedto simulated sunlight, show greater cytotoxicity compared to pristine ones, with LC50 ranging from15 to 23 nM. Using a combination of spectroscopic and microscopic techniques, we characterize thedegradation kinetics and transformation products of single- and double-shell QDs, when exposedto solar light at high temperature, simulating environmental conditions. Non-toxic pristine QDsdegrade to form toxic In–phosphate, In–carboxylate, Zn–phosphate, and oxidized Se, all of whichprecipitate as heterogeneous deposits. Comparison of their degradation kinetics highlights that theQDs bearing the thickest ZnS outer shell are, as expected, the most resistant to photodegradationamong the three tested QDs, as gradient shell, thin shell, and thick shell QDs lose their opticalproperties in less than 15 min, 60 min, and more than 90 min, respectively. They exhibit the highestphotoluminescence efficiency, i.e., the best functionality, with a photoluminescence quantum yield inaqueous solution of 24%, as compared to 18% for the gradient shell and thin shell QDs. Therefore,they can be considered as safer-by-design QDs

Influence of the Core/Shell Structure of Indium Phosphide Based Quantum Dots on Their Photostability and Cytotoxicity

International audienceWith the goal to improve their photostability, InP-based QDs are passivated with three types of inorganic shells, namely (i) a gradient ZnSexS1-x shell, (ii) an additional ZnS shell on top of the gradient shell with two different thicknesses (core/shell/shell, CSS), (iii) an alumina coating on top of ZnS. All three systems have photoluminescence quantum yields (PLQY) > 50% and similar PL decay times (64-67 ns). To assess their photostability they are incorporated into a transparent poly (methyl methacrylate) (PMMA) matrix and exposed to continuous irradiation with simulated sunlight in a climate chamber. The alumina coated core/shell system exhibits the highest stability in terms of PLQY retention as well as the lowest shift of the PL maximum and lowest increase of the PL linewidth, followed by the CSS QDs and finally the gradient shell system. By means of XPS studies we identify the degradation of the ZnS outer layer and concomitant oxidation of the emissive InZnP core as the main origins of degradation in the gradient structure. These modifications do not occur in the case of the alumina-capped sample, which exhibits excellent chemical stability. The gradient shell and CSS systems could be transferred to the aqueous phase using surface ligand exchange with penicillamine. Cytotoxicity studies on human primary keratinocytes revealed that exposure for 24 h to 6.25-100 nM of QDs did not affect cell viability. However, a trend toward reduced cell proliferation is observed for higher concentrations of gradient shell and CSS QDs with a thin ZnS shell, while CSS QDs with a thicker ZnS shell do not exhibit any impact

Toxicity to RAW264.7 Macrophages of Silica Nanoparticles and the E551 Food Additive, in Combination with Genotoxic Agents

International audienceSynthetic amorphous silica (SAS) is used in a plethora of applications and included in many daily products to which humans are exposed via inhalation, ingestion, or skin contact. This poses the question of their potential toxicity, particularly towards macrophages, which show specific sensitivity to this material. SAS represents an ideal candidate for the adsorption of environmental contaminants due to its large surface area and could consequently modulate their toxicity. In this study, we assessed the toxicity towards macrophages and intestinal epithelial cells of three SAS particles, either isolated SiO 2 nanoparticles (LS30) or SiO 2 particles composed of agglomerated-aggregates of fused primary particles, either food-grade (E551) or non-food-grade (Fumed silica). These particles were applied to cells either alone or in combination with genotoxic co-contaminants, i.e., benzo[a]pyrene (B[a]P) and methane methylsulfonate (MMS). We show that macrophages are much more sensitive to these toxic agents than a non-differenciated co-culture of Caco-2 and HT29-MTX cells, used here as a model of intestinal epithelium. Co-exposure to SiO 2 and MMS causes DNA damage in a synergistic way, which is not explained by the modulation of DNA repair protein mRNA expression. Together, this suggests that SiO 2 particles could adsorb genotoxic agents on their surface and, consequently, increase their DNA damaging potential

Assessment of oxidative damage induced by iron oxide nanoparticles on different nervous system cells

International audienc

Differential proteomics highlights macrophage-specific responses to amorphous silica nanoparticles

International audienceThe technological and economic benefits of engineered nanomaterials may be offset by their adverse effects on living organisms. One of the highly produced nanomaterials under such scrutiny is amorphous silica nanoparticles, which are known to have an appreciable, although reversible, inflammatory potential. This is due to their selective toxicity toward macrophages, and it is thus important to study the cellular responses of this cell type to silica nanoparticles to better understand the direct or indirect adverse effects of nanosilica. We have here studied the responses of the RAW264.7 murine macrophage cells and of the control MPC11 plasma cells to subtoxic concentrations of nanosilica, using a combination of pro-teomic and targeted approaches. This allowed us to document alterations in the cellular cytoskeleton, in the phagocytic capacity of the cells as well as their ability to respond to bacterial stimuli. More surprisingly, silica nanoparticles also induce a greater sensitivity of macrophages to DNA alkylating agents, such as styrene oxide, even at doses which do not induce any appreciable cell death

Toxicological impact of acute exposure to E171 food additive and TiO2 nanoparticles on a co-culture of Caco-2 and HT29-MTX intestinal cells

International audienceTiO2 particles are widely used in products for everyday consumption, such as cosmetics and food; their possible adverse effects on human health must therefore be investigated. The aim of this study was to document in vitro impact of the food additive E171, i.e. TiO2, and of TiO2 nanoparticles, on a co-culture of Caco-2 and HT29-MTX cells, which is an in vitro model for human intestine. Cells were exposed to TiO2 particles three days after seeding, i.e. while they were not fully differentiated. Cell viability, reactive oxygen species (ROS) levels and DNA integrity were assessed, by MTT assay, DCFH-DA assay, alkaline and Fpg-modified comet assay and 8-oxo-dGuo measurement by HPLC-MS/MS. The mRNA expression of genes involved in ROS regulation, DNA repair via base-excision repair, and endoplasmic reticulum stress was assessed by RT-qPCR. Exposure to TiO2 particles resulted in increased intracellular ROS levels, but did not impair cell viability and did not cause any oxidative damage to DNA. Only minor changes in mRNA expression were detected. Altogether, this shows that E171 food additive and TiO2 nanoparticles only produce minor effects to this in vitro intestinal cell model