Ultra small carbon nanodots as fluorescence markers in primary human cells: uptake and cellular distribution*

Carbon nanodots (CNDs) are promising candidates for fluorescence labeling of cellular components as well as for drug and gene delivery. Therefore, the uptake dynamics of CNDs and their cellular distribution are of vital interest. Here, we report the preparation of CNDS by a simple pyrolysis process, their structural and spectroscopic characterization, and the observation of cell-specific uptake rates by the leukocyte family as well as for hematopoietic stem cells. Large uptake rates are observed, resulting in up to approximately $10^9$ CNDs per cell after 24 hours of incubation. [1] The CNDs distribute non-uniformly across the cells. In particular, they do not enter the nucleus and have a tendency to accumulate in the Golgi apparatus in living cells. Fixation of the cells leads to a homogenization of the CND distribution across the cytoplasm. We show that this behavior suggests uptake via endocytosis, followed by intra-cellular storage inside nanoscale vesicles. Furthermore, the CNDs have only a small effect on the cell viabilities over a period of 72 hours even at very large CND concentrations.
[1] S. Fasbender et al., RSC Advances 7, 12208 (2017).