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Graphene quantum dots (GQDs) have gained popularity in nano-biotechnology due to their multifunctional delivery and imaging capabilities. The outcome of their therapeutic delivery applications relies on understanding cell internalization routes. Current literature presents often conflicting results based on surveying only a few endocytosis inhibitors. Herein, a holistic approach to cell uptake studies by utilizing six different inhibitors while considering their on- and off-target effects on internalization of the GQDs of different charges is provided. Endocytosis paths are explored by tracking intracellular GQD fluorescence in HeLa or HEK-293 cells. Contrary to the previous assumptions of a singular entry route, findings suggest that GQDs enter the cells through several endocytosis paths with some more prevalent than others. Selectivity between the pathways is based on GQD charge and functional groups. Positively charged nitrogen-doped GQDs (NGQDs) predominantly utilize a fast endophilin-mediated endocytosis (FEME) in HeLa cells with a secondary preference for clathrin-mediated endocytosis (CME). In HEK-293 cells NGQDs internalize via clathrin-independent, glycosylphosphatidylinositol-anchored protein-enriched compartments (CLIC/GEEC) and FEME. Conversely, GQDs with a substantial negative surface charge uptake through CME in HeLa cells. The optimization of these mechanisms can enhance GQD applications in biomedicine, ideally streamlining their translation into the clinic.
Topkiran et al. (Sun,) studied this question.