Biosynthesis of ZnO nanoparticles using fresh and dried leaf extracts of Moringa oleifera, Hibiscus sabdariffa, Centella asiatica, and Triticum aestivum for antimicrobial and antioxidant applications

Zinc oxide nanoparticles (ZnO NPs) have attracted major scientific interest due to their biocompatibility, photocatalytic nature, and promising antibacterial and antioxidant properties. In the present work, an eco-friendly biosynthesis approach was employed to synthesize ZnO nanoparticles using fresh and dried leaf extracts of four plants, namely Moringa oleifera, Hibiscus sabdariffa, Centella asiatica , and Triticum aestivum . This study presents an innovative eco-friendly method for synthesizing ZnO NPs, exploring the effect of extraction state (fresh and dried) on nanoparticle formation, optical properties, and biological performance. The ZnO NPs are prepared by biosynthesis with zinc salt as a precursor and leaf extracts as stabilizing and reducing agents. Characterisation using UV-Vis diffuse reflectance spectroscopy showed absorption edge between 350 and 370 nm with bandgap energies of 3.10-3.20 eV, confirming nanoscale bandgap modifications. X-ray Diffraction analysis validated the hexagonal wurtzite phase with crystallite sizes ranging from 8 to 18 nm. The FT-IR spectrum shows the presences of phytochemicals on the ZnO NPs surface. The morphology and elemental composition were examined using Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray analysis, revealing quasi-spherical particles mostly composed of Zn and O. High Resolution Transmission Electron Microscopy confirmed nano crystallinity with d-spacing values of 0.239-0.279 nm corresponding to (101), (100) and (002) planes. The zeta potential values (-10.3 to -15.5 mV) indicated moderate electro steric colloidal stability. Antibacterial tests showed substantial activity against Staphylococcus aureus and Escherichia coli , with roselle-derived ZnO NPs showing a higher inhibitory zone (at 1000 µg/ml). The DPPH assay demonstrated progressive radical scavenging with nanoparticle concentration, with roselle and moringa showing superior electron-donating capacity. This study shows the effects of plant extracts based on fresh and dried versions of the leaves and their impact on NPs properties.