The effect of surface charge on the cytotoxicity and uptake of carbon quantum dots in human umbilical cord derived mesenchymal stem cells

Carbon quantum dots (CQDs) are emerging as an ideal agent for efficient stem cell labeling. In current study, we synthesized a series of CQDs carrying different surface charges by changing the mass ratio of diammonium citrate (DC) and spermidine (Spd), and evaluated the effects of different surface charges on the cytotoxicity, cellular uptake, stability in human umbilical cord derived mesenchymal stem cells (hUCMSCs). We ascertained the optimal labeling time (24 h) and subtoxic concentration (50 mu g/mL) of all different charged CQDs. Our results demonstrated that, although positively charged CQDs are more cytotoxic and have lower photoluminescence (PL) compared to negative CQDs, they still have higher labeling efficiency for their higher uptake capacity. We found that relatively weak positive surface charges enabled CQDs to possess good biocompatibility and labeling efficiency in hUCMSCs. This work will helpfully contribute to the design and optimization of CQDs for tracking stem cells and further benefit to clinical research and application.