Cd-containing quantum dots transform during simulated human digestion causing increased adverse subcellular effects to intestinal cells

Abstract

Nanomaterials (NMs) entering the human body via the oral route are subjected to successive digestive chambers in the gastrointestinal (GI) tract, which could alter their physicochemical properties and toxicity profile. Commercially used quantum dots (QDs) exemplify emerging composite nanomaterials and can be used as the model material for transformation analysis, enabled by easier tracking and characterization due to their fluorescence properties. We synthesized a functional QD (CdSe/ZnS_P&E) according to a patented and commercially used QD, and subjected the particles to a three-phase simulated digestion process, consisting of salivary, gastric, and intestinal digestion. Size, surface chemistry, and dissolution extents were characterized before and after each digestion stage with the corresponding toxicity investigated on human intestinal epithelial cells (HIEC-6). The aggregation of QDs was minimally changed in the oral stage but metal components in aggregates decreased 60% in successive stages. Further, we observed the dissolution of up to 95% of zinc shells and the dynamic exchange of surface-adsorbed molecules with the surrounding matrix. In comparison to QD prior digestion, the salivary stage caused a decrease in QD cytotoxicity, whereas after the gastric and intestinal phases saw an increase in their cytotoxicity. Overall, this study advances our understanding of the transformation of complex NMs in the dynamic physiological environment of the human GI tract.