Colloidal semiconductor nanocrystals (quantum dots) possess unique optical properties, which make them attractive emitters for diverse applications such as optoelectronic devices or biomedical applications. During their life cycle, aging of quantum dots can lead to their dissolution and induce high toxicity due to the release of toxic chemical compounds. In this context In-based QDs have been proposed as less hazardous than the more popular Cd-based QDs.<br/>We compared the toxicity and fate of In-based QDs, either in their pristine form, or after artificial weathering in a climatic chamber. These QDs had an alloyed core composed of InZnP or InPZnS, and a gradient shell composed of Zn(Se,S). They were transferred from the organic to the aqueous phase using either penicillamine or glutathione as novel surface ligands.<br/>First, the kinetics of the QD physicochemical transformations during the aging process were studied by means of photophysical characterization. The major transformation products were identified using X-ray absorption spectroscopy and scanning-transmission electron microscopy coupled to energy-dispersive X-ray spectroscopy. Second, the toxicity of these QDs was evaluated in vitro on primary human keratinocytes, and in vivo using the freshwater polyp Hydra Vulgaris as model organism.<br/>Our results indicate that the physicochemical transformation of QDs in the climatic chamber is very rapid, with a total transformation occurring during the first two hours of ageing. Transformation occurs via both dissolution and precipitation of large aggregates where Se and S segregate from In, P, and Zn. The transformation products are much more toxic than pristine QDs. Core/shell QDs are safer than core QDs, and QDs with a core composed of InPZnS appear to be slightly safer than QDs with a core composed of InPZn. On the other hand, the nature of the surface ligand has no detectable influence on QD toxicity. Importantly, also in Hydra tissues speciation using XANES confirms the fast dynamics of QD degradation. Both InP-based core and core/shell QDs are far less toxic compared to penicillamine coated CdSe/ZnS QDs and their stability can be increased by growing on top of the gradient shell an additional ZnS shell.

Influence of composition and surface state on the toxicity and fate of indium phosphide quantum dots

2019 Spring National Meeting

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