Green synthesis of quercetin-mediated ZnS quantum dots and their photocatalytic, antimicrobial, and cytotoxic performances

In this study, ZnS quantum dots (QDs) were synthesized via a green, simple, cost-effective, and sustainable method using quercetin as a reducing and stabilizing agent. Successful synthesis was confirmed by UV–vis and Photoluminescence (PL) spectroscopy, revealing characteristic optical properties. Structural and morphological features were analyzed by ATR-FTIR, XRD, SEM–EDX, and TEM, showing crystallinity, surface functionalities, and nanostructure, with TEM confirming particle sizes ≤ 10 nm. The anti-biofilm activity was tested against E. coli ATCC 35218 and P. aeruginosa ATCC 27853, showing significant inhibition, especially against E. coli. Antifungal activity against C. albicans ATCC 10239 (agar disk diffusion) revealed larger inhibition zone (22 mm) than the reference antibiotic (20 mm). The MTT assay revealed high biocompatibility, with L929 fibroblast cell viability remaining above 75% across all test conditions. Under 24 h of UV irradiation, the photocatalytic degradation efficiency reached 85% for Brilliant Green (BG) and approximately 70% for Methylene Blue (MB). Photoluminescence stability was examined between 0–40 °C, showing good thermal stability with minimal structural degradation. These results suggest ZnS QDs possess promising antimicrobial, antifungal, photocatalytic, and biocompatible properties, supporting their potential in biomedical and environmental applications.