Nanotoxicity of fruit based carbon-dots using in vitro and in vivo models

Fluorescent carbon-dots (c-dots) are a class of recently discovered nanomaterials. C-dots are appealing considerable attention as benign substitutes of quantum dots, due to their small particle size (<10 nm), aqueous solubility and excellent biocompatibility. In addition to that, the possibility of preparing c-dots from natural products, such as fruits, attracted the study of these nanomaterials for applications in bioimaging, biosensing and drug delivery. In this way, information on their toxicological profile both in vitro and in vivo is crucial. To the best of our knowledge c-dots produced from fruits have been studied for the first time for their toxicity against cells and zebrafish embryos in this work. Here, three different c-dots synthesized from kiwi, pear and avocado fruits respectively, by one-pot green hydrothermal method, and characterized for their photoluminescence properties, were used. The potential toxicity of these nanoparticles was addressed using in vitro and in vivo models. Conventional in vitro cytotoxicity and anticancer potential of fruit based c-dots tests were performed using normal cells (human kidney derived) and cancer cells (human epithelial colorectal adenocarcinoma). In vivo toxicity was determined using zebrafish Danio rerio (Hamilton, 1822) given its peculiar embryogenesis with transparent embryos developing ex-utero, allowing for a real-time analysis. This model was also addressed to validate the internalization and distribution of novel fruit based c-dots by confocal imaging. It was found that the tested fruit based c-dots only presented toxicity at concentrations above 1.5 g/L in both in vitro and in vivo assays. Kiwi c-dots showed to be the most toxic to both cells and zebrafish embryos, presenting lower LD50 values. Conversely, c-dots synthesized from citric acid (commercial soruce reference) did not present toxicity. However, pepper c-dots (nonfruit reference) induced different toxicity towards cells and zebrafish. This suggests that the effects observed can be attributed to the starting material employed in their synthesis. The distribution of c-dots in zebrafish embryos was observed from their fluorescence emission especially in the eye and yolk sac, being avocado c-dots the ones more accumulated.