Fine-Tuning Positive-Surface-Charge Carbon Dots for High-Efficiency and Low-Cytotoxicity Gene Delivery

Carbon dots (CDs) have emerged as a promising non-viral gene delivery vector due to their excellent biocompatibility and tunable surface properties. In this study, four CDs with gradient-positive zeta potentials (7.23 mV, 16.7 mV, 25.3 mV, 34.5 mV) were synthesized via a hydrothermal method. Among these, CDs-3 with an optimal zeta potential of 25.3 mV stood out, exhibiting ultra-low cytotoxicity (cell viability > 80% even at 50 μg/mL) and a transfection efficiency of nearly 100% (for GFP plasmid delivery), significantly outperforming commercial vectors Lipo2000 and PEI. A stable CDs-3/siIhh delivery system was constructed at a mass ratio of 2:1. In vitro evaluations confirmed that CDs-3/siIhh could efficiently regulate the Indian Hedgehog (Ihh) signaling pathway and osteoarthritis (OA)-related markers in both normal and IL-1β-induced inflammatory ATDC5 chondrocytes. Its regulatory effect was significantly superior to that of the commercial Lipo2000/siIhh and PEI/siIhh systems. This consistent "transcription-translation" regulation, combined with the carrier's safety and excellent cellular internalization capacity in chondrocytes, highlights its potential for OA gene therapy. Collectively, our work develops a novel, safe, and efficient positive-potential CD-based gene delivery vector, providing a promising gene regulatory capacity by leveraging optimized surface charge engineering.