| Carbon nanomaterials is an important part of the artificial synthesis of nanomaterials. Recent advancements in carbonaceous nanomaterials research have opened up a wide range of applications in electrochemical devices, energy storage, cell imaging, drug delivery, biosensors. Graphene oxide, graphene oxide quantum dots and carbon nanotubes, which are members of the family of carbon nanomaterials, perform well in these areas. Given the potential occupational and public exposure to and biosafety aspect of carbonaceous nanomaterials due to its versatile applications. This problem should pay the attention of scientists, and assess the risks of carbonaceous nanomaterials to health and the ecosystem as soon as possible. However, this kind of work is relatively scarce at present. This study is trying to compare three typical carbon nanomaterials on the toxicity effect of chlorella to evaluate the risks of carbonaceous nanomaterials to health and the ecosystem, and also to explain the mechanism of nanotoxicology.First, the nanotoxicology of typical graphene oxide(GO) and carboxyl single-walled carbon nanotubes(C-SWCNT) was compared. The results showed that cell division of Chlorella vulgaris was promoted at 24 h and then inhibited at 96 h after nanomaterial exposure. At 96 h, GO and CSWCNT inhibited the rates of cell division by 0.08-15% and 0.8-28.3%, respectively. Both GO and C-SWCNT covered the cell surface, but the uptake percentage of C-SWCNT was 2-fold higher than that of GO. C-SWCNT induced stronger plasmolysis and mitochondrial membrane potential loss and decreased the cell viability to a greater extent than GO. Moreover, C-SWCNT-exposed cells exhibited more starch grains and lysosome formation and higher reactive oxygen species(ROS) levels than GO-exposed cells. Metabolomics analysis revealed significant differences in the metabolic profiles among the control, C-SWCNT and GO groups. The metabolisms of alkanes, lysine, octadecadienoic acid and valine was associated with ROS and could be considered as new biomarkers of ROS. The nanotoxicological mechanisms involved the inhibition of fatty acid, amino acid and small molecule acid metabolisms. These findings provided theoretical support into the effects of GO and C-SWCNT on cellular responses.The interactions between nanomaterials and cells are fundamental in biological responses to nanomaterials. However, the size-dependent synergistic effects of envelopment and internalization as well as the metabolic mechanisms of nanomaterials have remained unknown. The nanomaterials tested here were larger graphene oxide nanosheets(GO) and small graphene oxide quantum dots(GOQD). GO intensively entrapped single-celled Chlorella vulgaris, and envelopment by GO reduced the cell permeability. In contrast, GOQD-induced remarkable shrinkage of the plasma membrane and then enhanced cell permeability through strong internalization effects such as plasmolysis, uptake of nanomaterials, an oxidative stress increase, and inhibition of cell division and chlorophyll biosynthesis. Metabolomics with OPLS-DA analysis showed that amino acid metabolism was sensitive to nanomaterial exposure. Shrinkage of the plasma membrane may be linked to increases in the isoleucine levels. The inhibition of cell division and chlorophyll a biosynthesis may be associated with decreases in aspartic acid and serine, the precursors of chlorophyll a. The increases in mitochondrial membrane potential loss and oxidative stress were correlated with an increase in linolenic acid. The above metabolites can be used as indicators of the corresponding biological responses. These results enhance our systemic understanding of the size-dependent biological effects of nanomaterials. |
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