N, O-Functionalized Curcumin-Derived Carbon Dots for Reactive Oxygen Species Regulation: Mechanistic Insights into Biomedical Applications

A mechanistic understanding of reactive oxygen species (ROS) regulation in N- and O-functionalized curcumin-derived carbon dots (Cur-CDs) has been elucidated through integrated experimental and time-dependent density functional theory (TD-DFT) studies. Cur-CDs were synthesized via a green hydrothermal method, yielding sub-10 nm, water-dispersible particles exhibiting broad UV-NIR absorption and bright blue photoluminescence. Photothermal conversion efficiency was measured at 29.6%, and time-resolved photoluminescence revealed a radiative lifetime of 1.8 ns and a dominant nonradiative decay component of 6.1 ns, suggesting both emissive and heat-dissipating pathways. TD-DFT calculations suggest that pyrrolic-N and graphitic-N surface functionalities reduce the singlet-triplet energy gap (ΔE_ST to 0.33 eV), which may promote intersystem crossing and facilitate light-induced ROS generation. In vitro assays indicated selective cytotoxicity toward HepG2 cancer cells (IC₅₀ = 200 ppm) relative to mesenchymal stem cells (IC₅₀ = 222.32 ppm), and fluorescence imaging showed an effective cellular uptake. These findings indicate the potential of Cur-CDs as multifunctional agents for cancer diagnostics and therapy. The integration of mechanistic analysis and functional evaluation positions Cur-CDs as a promising and sustainable nanomaterial for biomedical applications, while contributing to the broader understanding of structure-property relationships in ROS-active carbon-based systems.