Carbon dot (CD)-based multifunctional delivery systems have shown great potential in both drug/gene delivery and bio-imaging. In this work, we present a strategy to simply construct amphiphilic CDs (ACDs) by conjugating hydrophobic alkyl epoxide to the surface amino groups of PEI 600-derived CDs. ACDs could well dissolve in water or organic solvents and emit bright fluorescence both in solutions and cells. ¹HNMR also suggested that ACDs may form micelle-like structures in water, and their CMC could be determined. Enhanced green fluorescent protein (EGFP) expression and flow cytometry experiments showed that ACDs have higher transfection efficiency than Lipofectamine 2000 in A549 cells. Besides DNA, ACDs could also effectively transfect Sur siRNA toward A549 cells and cause early cell apoptosis. The 3D multicellular spheroids further confirmed their high potential for delivering therapeutic genes into the tumor tissue. On the other hand, ACDs also exhibited good drug loading ability. CLSM experiment results showed that DOX could be effectively internalized by the cell and slowly released from the drug/ACD complex. These results suggest that ACDs may not only serve as versatile delivery vectors with potential for applications in clinical cancer treatment, but also offer an inspiration for the discovery of CD-based gene/drug delivery systems.

Nano-theranostic agents play important roles in the development of therapeutic methods for serious diseases. In this study, novel carbon dots (CDs) L-CD/C-CD were prepared from Gd(III) salt/complexes, cationic polymers and citric acid in the hope that they would combine the abilities of gene delivery and multi-modal (MR/FL) imaging. The CDs inherited the properties of good water-solubility and positive charge from their precursor polymers. In vitro gene transfection results showed that the CDs have good transfection efficiency and anti-serum ability, especially for L-CD, which has 74 times higher transfection efficiency than PEI 25 kDa in the presence of 10% serum. The CDs exhibited bright fluorescence, which was stable for several days under various pH. Confocal laser scanning microscopy revealed that the CDs could image HeLa cells with blue or green fluorescence well, and realize the monitoring of the gene delivery process. Besides, the CDs showed favorable biocompatibility with excellent performance in longitudinal relaxivity rates (r₁) of 11.4 mM⁻¹ s⁻¹ for L-CD and 57.6 mM⁻¹ s⁻¹ for C-CD, which were about 3–15 times higher than that of the clinical Gd reagent Gd-DTPA (3.75 mM⁻¹ s⁻¹). Furthermore, the CDs could perform in vivo tumor-specific MR-imaging more clearly than Gd-DTPA, which is attributed to their suitable particle size and their resulting greater accumulation at tumor site via the EPR effect. This study provides a promising strategy for constructing multi-functional CDs for tumor theranostics.

A strategy that uses hyaluronic acid (HA) as a carbon source and polyethylenimine (PEI) as a passivant to construct carbon dots (HA-Cds) was proposed. The synthetic method is simple and green and no additive was required. These carbon dots could emit strong blue fluorescence under UV light. FT-IR and ¹H NMR spectra confirmed that part of characteristic residues of HA and PEI remained in the HA-Cds structure. These materials had much lower cytotoxicity than PEI and high serum tolerance. Up to 50 times higher transfection efficiency than that of PEI was obtained in the presence of 10% serum. BSA protein adsorption, flow cytometry, and confocal microscopy assays also supported their good performance with serum. Furthermore, as multifunctional materials, HA-Cds had good intracellular imaging ability and displayed tunable fluorescence emission under varying excitation wavelengths. An HA competition assay showed that they may have target cell imaging ability in CD44 overexpressed cells. These materials with fluorescence activity also facilitated co-localization experiments by CLSM, which revealed that the DNA cargo could be effectively released into the cytosol, leading to effective gene transfection. These properties make the carbon dots promising candidates for in vivo diagnosis and gene therapy.

Carbon dots (CDs) are photoluminescent nanoparticles with distinctive properties, having great potential in nano-biomaterial systems such as gene/drug delivery vectors and cell imaging agents. Fluorine-doped CD C-6F was prepared by a one-step ring-opening polymerization-dehydrative carbonization (RPDC) approach based on low molecular weight polyethyleneimine (PEI, 600 Da) and fluorinated diglycidyl ethers, while the non-fluorinated counterpart C-6H and the CD prepared from PEI 600 Da solely (C-600) were also prepared for comparison. TEM, FT-IR and XPS were performed to determine the compositions and surface states of the CDs. In vitro cell experiment results reveal that the CDs prepared from RPDC approach have much higher transfection efficiency and cellular uptake than PEI 600 contrasts in various cell lines. Compared to non-fluorinated C-6H, C-6F exhibited distinctly higher transfection efficiency, and up to 30 and 260 times higher efficiency than PEI 25 kDa could be achieved in the absence and presence of serum, respectively, indicating the advantage of F-doping. Besides, these CDs exhibit good cell imaging capability under single wavelength excitation, making the materials suitable for cellular tracking and transfection mechanism studies. These results demonstrate that fluorine-doping is an efficient approach to obtained CD gene vectors with high efficiency and serum tolerance.