Green Synthesis and Characterization of Zinc Oxide Nanoparticles Using Ehretia Cymosa Leaf Extract and Evaluation of Antimicrobial Efficacy

This study focuses on an eco-friendly and cost-effective green synthesis of zinc oxide nanoparticles using the aqueous leaf extract of Ehretia cymosa as a natural capping and stabilizing agent, combined with zinc acetate dihydrate as a precursor. Synthesis was conducted across various volumetric precursor-to-extract ratios (1:1, 1:2, and 1:3 v/v) at pH 12, followed by thermal annealing at 500°C. X-ray diffraction analysis confirmed the formation of phase-pure, highly crystalline ZnO NPs featuring a hexagonal wurtzite crystal structure. Based on the Debye-Scherrer equation, the calculated average crystallite sizes were 17.84 nm for the 1:1 ratio and 18.25 nm for the 1:3 ratio. The smaller particle size observed in the 1:1 formulation is attributed to higher concentrations of phytochemical capping agents that prevented nanoparticle aggregation. The antibacterial efficacy of the synthesized ZnO NPs was evaluated against Gram-negative ( Escherichia coli ) and Gram-positive ( Staphylococcus aureus ) bacterial strains using the disc diffusion method. The nanoparticles exhibited strong, dose-dependent antibacterial activity against both pathogens. Higher antibacterial susceptibility was observed in S. aureus (26 mm inhibition zone at 0.04 mg/mL) compared to E. coli (25 mm inhibition zone at 0.04 mg/mL). This differential sensitivity is linked to structural variations in their cell walls, as the outer membrane of Gram-negative bacteria acts as a partial permeability barrier. Generally, Ehretia cymosa leaf extract provides a sustainable biological platform for producing functional ZnO nanomaterials with effective antimicrobial properties.