Green-Synthesized Carbon Quantum Dots (CQDs): Integrated Spectroscopic and Computational Investigation of Bovine Serum Albumin (BSA) Binding Interaction

Carbon quantum dots (CQDs) have recently gained significant attention in biological applications due to their low toxicity and high biocompatibility. However, there are still limited studies on how they interact in biological systems. In this study, CQDs were green-synthesized from capsicum and their formation was confirmed through XRD, HR-TEM, XPS, FTIR, UV–visible, and PL spectroscopy. The binding interaction mechanism of the BSA–CQD complex system was systematically investigated by using various biophysical techniques. Steady-state fluorescence studies revealed that CQDs induce fluorescence quenching of BSA predominantly through a static quenching mechanism. CD spectroscopy confirmed that CQD binding changes the secondary structure of BSA. Thermodynamic analysis showed a negative Gibbs free energy change (−3.5 kcal/mol), indicating that the interaction is spontaneous and driven by hydrogen bonds and van der Waals forces. Since synthesized CQDs are amorphous, we carried out an atomistic modeling with DFT and TD-DFT, guided by experimentally obtained FTIR and UV–visible spectra. Additionally, molecular docking simulations supported our experimental results by identifying hydrogen bonds and van der Waals interactions as the main forces in the BSA–CQD complex. Molecular dynamics simulations and single-point DFT calculations provided further insights into the stability and interaction behavior of CQDs within the BSA complex system.