Preparation of turmeric-derived sulfur-functionalized carbon dots: antibacterial and antioxidant activity

The work describes the preparation of carbon dots using turmeric as the carbon source and their functionalization with sulfur to enhance the functionality. The turmeric-derived carbon dots (CD) and sulfur-functionalized carbon dots (S-CD) were fabricated by a hydrothermal method. The prepared CD was in size range of 10 nm as confirmed by FETEM, and the sulfur functionalization of the CD was verified by FTIR and XPS tests. The CD showed a clear color change from yellowish-brown to green under UV light and exhibited tunable photoluminescence properties. Both CD and S-CD showed strong antioxidant activity in DPPH and ABTS assays. In addition, the S-CD exhibited potent antibacterial activity against E. coli and L. monocytogenes. The sulfur-functionalized CD produced more reactive oxygen than the non-functionalized CD, confirming the stronger antibacterial activity of S-CD. Additionally, the cytotoxicity of the CD was checked against fibroblast L929 cells, and results showed over 80% of viable cells at 1000 μg/mL for 72 h, indicating the low cytotoxicity. Therefore, multifunctional CD materials made from turmeric can be safely used for biomedical and food packaging applications.