Envelopment–Internalization Synergistic Effects and Metabolic Mechanisms of Graphene Oxide on Single-Cell Chlorella vulgaris Are Dependent on the Nanomaterial Particle Size

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 (GONS) and small graphene oxide quantum dots (GOQD). GONS intensively entrapped single-celled Chlorella vulgaris, and envelopment by GONS 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 analysis showed that amino acid metabolism was sensitive to nanomaterial exposure. Shrinkage of the plasma membrane is proposed to be linked to increases in the isoleucine levels. The inhibition of cell division and chlor...