Green Synthesis of Highly Luminescent Carbon Quantum Dots from Asafoetida and Their Antibacterial Properties

Highly luminescent carbon quantum dots (CQDs) and copper-doped CQDs (Cu-CQDs) were synthesized from Asafoetida powder using a one-pot hydrothermal method. The structural, morphological, and optical properties of the synthesized CQDs were characterized via microscopic and spectroscopic techniques. Photoluminescence studies revealed that CQDs exhibited maximum emission at 450 nm under 335 nm excitation with a quantum yield of 37%, while Cu-CQDs showed a red-shifted emission at 455 nm under 330 nm excitation and a significantly enhanced quantum yield of 73.4%. As a proof of concept for potential biomedical and surface-coating applications, the antimicrobial activity of both CQDs was evaluated against <i>Escherichia coli</i> (<i>E. coli</i>) and <i>Staphylococcus aureus</i> (<i>S. aureus</i>). Cu-CQDs exhibited superior antibacterial efficacy, with a minimum inhibitory concentration of 0.3 mg mL^-1. Furthermore, Cu-CQDs were immobilized on polyvinyl chloride (PVC) surface, and fluorescence microscopy confirmed their antibacterial effectiveness, demonstrating their potential for functionalized antimicrobial coatings.