Multifunctional ZnO Nanoparticles Synthesized Using Spirodela polyrhiza Extract: Characterization, Photocatalytic...

This study investigates the green synthesis of zinc oxide nanoparticles (ZnO NPs) using the aqueous extract of the aquatic plant Spirodela polyrhiza (greater duckweed) and evaluates their multifunctional properties. The ZnO NPs were synthesized via a sustainable method and characterized using UV-visible spectroscopy, TEM, FESEM, EDX, FTIR, and XRD analyses. UV-visible spectroscopy confirmed the formation of ZnO NPs with a characteristic absorption peak at ∼349 nm. TEM and FESEM analyses revealed spherical and nonspherical particles ranging from 20 to 70 nm. The antimicrobial activity of ZnO NPs was assessed against three bacterial strains (Escherichia coli, Staphylococcus aureus, and Bacillus subtilis) and three fungal strains (Aspergillus niger, Penicillium chrysogenum, and Candida albicans). Notably, B. subtilis showed a maximum inhibition zone of 18 mm at 100 mg/mL, while A. niger exhibited the highest antifungal response with a zone of 22 mm and an activity index (AI) of 1.15, indicating comparable or superior activity to ketoconazole at higher concentrations. Molecular docking simulations using the crystal structure of B. subtilis YmaH (Hfq) protein (PDB ID: 3HSB) revealed strong noncovalent interactions with Zn atoms of the NPs, particularly involving HIS57 and LEU26 residues. Additionally, ZnO NPs demonstrated a noteworthy photocatalytic degradation (90.4%) of methylene blue dye under sunlight exposure. These results highlight the potential of S. polyrhiza-mediated ZnO NPs for use in antimicrobial therapies and environmental remediation applications.