Hydrophobically modified carbon dots as a multifunctional platform for serum-resistant gene delivery and cell imaging.

The development of novel multifunctional gene delivery systems with high efficiency is significant. Herein, due to the unique physical and optical properties of carbon dots (CDs), CDs prepared from polyethyleneimine (PEI) were modified with various hydrophobic chains and different degrees of substitution via an epoxide ring-opening reaction. The modification and substitution degree were confirmed using several analytical methods including 1H NMR spectroscopy, FT-IR spectroscopy, TEM, and XPS. These CDs were utilized as multifunctional, safe and efficient non-viral gene vectors. The results showed that these materials possessed capability for dual-channel imaging, which enabled the intracellular tracking of the delivered DNA. Both the type and substitution degree of the hydrophobic chain have a large influence on their transfection efficiency. Among the prepared CDs, Ole1.5-CD gave the highest transfection efficiency, which was up to 200 times higher than that of PEI 25 kDa in the presence of serum in A549 cells. Meanwhile, these CD materials showed much less cytotoxicity and better serum tolerance than the traditional cationic polymeric gene vector. The cellular uptake assay further confirmed the good serum tolerance and structure-activity relationship of the CD materials. Thus, these CDs with good biocompatibility, self-imaging and high gene transfection efficiency may serve as a promising platform for both gene delivery and bio-imaging.