Plant-mediated green synthesis of ZnO nanoparticles utilizing Garcinia cowa leaf extract: Structural, bioactive, and In Silico molecular docking insights

This study reports the green synthesis of zinc oxide nanoparticles (ZnO NPs) using Garcinia cowa leaf extract at varying precursor concentrations (0.1, 0.2, and 0.5 M) and compares their properties with chemically synthesized ZnO NPs. Structural characterization confirmed the formation of hexagonal wurtzite ZnO NPs with crystallite sizes ranging from 16.7 to 25.7 nm, as determined by X-ray diffraction (XRD) analysis. UV-Visible spectroscopy revealed a concentration-dependent band gap variation from 3.71 to 3.33 eV, indicating that with the particle size increase band gap decreased and is consistent with the quantum confinement effect. Fourier Transform Infrared Spectroscopy (FTIR) spectra exhibited characteristic Zn-O vibrational modes between 400 and 562 cm −1 , while electron microscopy (Field Emission Scanning Electron Microscopy (FESEM)/Transmission Electron Microscopy (TEM)) demonstrated quasi-spherical morphologies with average particle sizes increasing from 22.6 nm (green-synthesized) to 74.9 nm (chemically synthesized). Energy Dispersive X-ray Spectroscopy (EDX) analysis confirmed high purity with Zn:O atomic ratios approaching 1:1. The biosynthesized ZnO NPs displayed enhanced bioactivity, exhibiting up to 59.7 % DPPH radical scavenging at 400 μg/mL compared to 57.4 % for chemically synthesized NPs. Furthermore, antibacterial assays confirmed bactericidal properties against both Gram-positive ( B. subtilis ) and Gram-negative ( P. aeruginosa ) strains. In silico molecular docking studies provided mechanistic insights, showing strong binding affinities of −4.9 kcal/mol with subtilisin ( B. subtilis ) and −5.1 kcal/mol with RhlR quorum-sensing receptor ( P. aeruginosa ), involving key interactions with active site residues. ADMET predictions indicated a favorable safety profile for the green-synthesized ZnO NPs, with no predicted hepatotoxicity or mutagenicity. These findings demonstrate that Garcinia cowa -mediated synthesis produces ZnO NPs with excellent structural and bioactive properties, offering a sustainable alternative for biomedical and optoelectronic applications.