Photodynamic antibacterial potential of pomegranate peel-derived carbon quantum dots synthesized via pyrolytic and hydrothermal methods

In this study, carbon quantum dots (CQDs) were synthesized from pomegranate peel via pyrolytic (PY-ppCQD) and hydrothermal (HT-ppCQD) methods at 160 °C and 180 °C. Transmission electron microscopy (TEM) revealed uniformly dispersed nanoparticles with diameters ranging from 2 to 5 nm and lattice fringes indicative of graphitic carbon structures. FTIR and XPS analyses confirmed the presence of surface functional groups—such as hydroxyl, carboxyl, and carbonyl moieties—originating from the polyphenolic components of the raw biomass, indicating effective retention of bioactive functionalities. Cytotoxicity assessment using the MTT assay showed dose-dependent effects on HEK-293 cells, with significant inhibition observed at 800 μg/mL, supporting the selection of 0–400 μg/mL for subsequent antibacterial evaluations. The antibacterial efficacy of CQDs against Staphylococcus aureus (SA) was assessed via OD600 and colony-forming unit (CFU) measurements, revealing concentration-dependent growth inhibition, with PY-ppCQD exhibiting slightly superior activity compared to HT-ppCQD, particularly at 400 μg/mL. Under 440 nm blue light irradiation, antibacterial activity was significantly enhanced for both CQDs, attributed to the generation of reactive oxygen species (ROS) that induce bacterial membrane damage. Scanning electron microscopy (SEM) further confirmed morphological deformation and cell rupture, especially in the PY-ppCQD-treated groups under light exposure. These findings demonstrate that pomegranate peel-derived CQDs—particularly those prepared via pyrolysis—possess strong intrinsic and photo-enhanced antibacterial properties, highlighting their potential as sustainable and multifunctional nanomaterials for biomedical and antimicrobial applications.