The effect of surface charge on cellular uptake and inflammatory behavior of carbon dots

Abstract

Synthesis of carbon dots (CDs) or carbon quantum dots (QCDs) from different carbon sources have attracted much attention due to their excellent potential to advance wide range of applications such as biosensing, bioimaging, photoscience and other biomedical usage. However, the interaction of CDs (without any complex surface functionalities) with different cell lines especially with respect to their surface charge still needs to be elaborated in certain phenomena i.e. cytotoxicity, cellular uptake and inflammatory profiling. In this study, two oppositely charged CDs were synthesized and compared for their surface charge dependent interaction with different cell lines. Positively charged CDs were synthesized by using bovine serum albumin (BSA) and negatively charged CDs were synthesized using citric acid (CA) by acidic hydrolysis and reflux methods, respectively. Using both CDs, a concentration dependent cytotoxicity was carried out on 3T3 fibroblast, MDA-MB-231 breast cancer and RAW 264.7 macrophage cell lines, while cellular uptake and inflammatory studies were conducted with RAW 264.7 macrophages cell line. Results showed that both BSA and CA-CDs were not cytotoxic up to 400 μg/mL. Flow-cytometry studies indicated that cellular uptake of negatively charged CA-CDs was quite higher (~6.25%) than that of positively charged BSA-CDs (~1.24%). On the other hand, positively charged BSA-CDs have significantly enhanced the inflammatory cytokines release by RAW 264.7 macrophages cells. A concentration dependent increase in tumor necrosis factor alpha (TNF-α) and interleukin-6 (IL-6) was observed when RAW 264.7 macrophages cells were treated with BSA-CDs. In comparison, CA-CDs did not show any effect on these cytokines release. Therefore, it was concluded that the interaction of CDs with different cells is dependent on their surface charge which can also control their cellular influx and release of inflammatory cytokines.