Green-emitting carbon dots from Protocatechuic acid and branched PEI: A multifunctional platform for bioimaging and gene delivery.

Carbon nanodots (CNDs) have emerged as promising candidates for bioimaging and gene delivery due to their excellent photostability, biocompatibility, and tunable optical properties. In this study, green-emitting CNDs were synthesized via a microwave-assisted method using protocatechuic acid (AP) and high molecular weight branched polyethyleneimine (bPEI25kDa) as precursors. The resulting AP-PEI25k CNDs exhibited uniform spherical morphology (average particle size of 9.2 nm), strong photoluminescence emission centered at 520 nm (greenish-yellow), high colloidal stability in solution, and positive surface charge (favorable to boost electrostatic interactions with negatively charged plasmid DNA). Stability assays confirmed their resistance to photobleaching and temperature variations, as well as good colloidal stability under a wide range of pH conditions. The CNDs effectively condensed and partially protected plasmid DNA from enzymatic degradation, with in vitro studies on HeLa and HGF cells demonstrating efficient gene delivery and reduced cytotoxicity compared to bPEI25kDa. Fluorescence microscopy confirmed the CNDs uptake and intracellular localization in HeLa cells. These results highlight that the prepared AP-PEI25k CNDs are suitable multifunctional platforms to explore further in vivo biomedical applications in combined gene therapy and cellular imaging.