Cerium-doped carbon dots for multifunctional biomedical applications: enhanced heavy metal sensing, antioxidant-driven wound healing, and RAFT polymer-mediated improved gene complexation capability.

Highly fluorescent cerium-doped carbon dots (Ce-CDs) were synthesized via a facile hydrothermal process using citric acid, urea, and cerous nitrate hexahydrate. Cerium incorporation markedly enhanced the fluorescence intensity and introduced a unique time-dependent colour evolution from dark green to red. The Ce-CDs exhibited selective heavy metal ion sensing behaviour, where Hg²⁺ caused an increase in absorbance intensity along with a blue shift of the absorption maximum, whereas Cd²⁺ and Pb²⁺ induced pronounced absorbance quenching. Beyond sensing, Ce-CDs demonstrated superior antioxidant activity in 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays compared to CDs, reflecting the contribution of the Ce³⁺/Ce⁴⁺ redox couple. This enhanced radical scavenging capability translated into improved biological performance. In vitro scratch assays using L929 fibroblast cells revealed complete wound closure within 24 h at Ce-CD concentrations of 50 and 100 µg/mL, while undoped CDs failed to achieve full healing under identical conditions. In addition, Ce-CDs showed significantly stronger antibacterial activity against Escherichia coli. To enable gene complexation capability, an amino acid-rich RAFT (Reversible Addition-Fragmentation Chain-Transfer) polymer, poly(hydroxyethyl methacrylate-phenylalanine-NH₂) (PHPA-NH₂), was conjugated onto Ce-CDs via carbodiimide coupling. Successful conjugation was confirmed by FTIR spectroscopy and a surface charge reversal from - 16.1 mV to + 40.5 mV. The resulting PHPA-NH₂@Ce-CDs efficiently condensed DNA at weight ratios ≥ 10:1, as confirmed by gel electrophoresis. Overall, cerium doping and polymer functionalization synergistically transform carbon dots into a multifunctional nanoplatform with strong potential for heavy metal sensing, wound healing, antibacterial therapy, and potential non-viral gene delivery platform applications.