Precursor-dependent modulation of DNA interaction in carbon quantum dots: Physico-chemical characterizations

Carbon Quantum dots (CQDs) have become a fascinating topic in nanobiotechnology, attributable to their tunable optical properties, versatile surface functionality, and biological compatibility. While applications of CQDs have been broad and diverse, a clear systematic understanding of the role of the precursor in the interaction mechanism with DNA has not been explored in depth. In this study, four structurally distinct CQDs from biomass and chemically derived precursors were synthesized to investigate their interaction with calf thymus DNA (ct-DNA). Each type of CQDs were characterized via UV-Visible spectroscopy, fluorescence spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Dynamic Light Scattering (DLS), zeta potential, Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray Spectroscopy (EDS), and X-Ray Photoelectron Spectroscopy (XPS). Interaction studies were carried out by UV-Visible absorption spectroscopy, competitive fluorescence displacement assays, Circular Dichroism (CD) spectroscopy, and Cyclic voltammetry (CV). Biomass-derived onion and tomato CQDs (OQDs, TQDs) showed sharp UV peaks at 283.5 nm along with negative zeta potentials and were bound with ct-DNA via external π-mediated surface association. The chemically derived thiourea and L-cysteine CQDs (UQDs, LQDs) showed sharp UV peaks at 338 nm and 332 nm respectively, along with positive surface charges and exhibited strong electrostatic and groove-directed binding with ct-DNA. UQDs exhibited the highest DNA-binding affinity (K_b = 1.77 × 10⁶ M^-1), among all four CQDs. All DNA interaction studies collectively supported predominantly non-intercalative interactions. This study might help in facilitating our understanding regarding nano-biorecognition, which may further be utilized for designing targeted CQD-based systems for various biomedical applications.