Phytogenic synthesis of ZnO nanoparticles: towards eco-friendly strategies for antibacterial applications

The accelerating threat of antimicrobial resistance (AMR) underscores the urgent need for sustainable, safe, and cost-effective alternatives to conventional antibiotics. The field of nanotechnology has advanced significantly, with zinc oxide nanoparticles (ZnO-NPs) gaining attention for their exceptional stability, biocompatibility, and strong antimicrobial potential. However, traditional fabrication techniques frequently utilize hazardous chemicals and require high energy inputs, leading to ecological and safety issues. In contrast, green synthesis mediated by plant extracts presents a viable, eco-friendly substitute. This approach is not only cost-effective and simple but also enhances nanomaterials (NMs) by integrating bioactive phytocompounds. This research employs a facile, green chemistry route to fabricate ZnO-NPs, utilizing pulp extracts from Agave azul (Agave tequilana), Chiku (Manilkara zapota), and Soursop (Annona muricata). acting as bio-reducing, stabilizing, and capping agents. Zinc acetate dihydrate was selected as the metal precursor, subjected to controlled thermal treatment and calcination. This methodology successfully yielded stable nanoparticles while completely avoiding the use of hazardous synthetic reagents. Comprehensive characterization confirmed the successful formation of ZnO-NPs. XRD validated their crystalline wurtzite structure, while electron microscopy revealed distinct morphologies: flower-like quasi-spherical aggregates for Agave-derived ZnO, mixed quasi-spherical and hexagonal particles for Chiku-derived ZnO, and predominantly quasi-spherical particles with occasional rod-like structures for Soursop-derived ZnO. The average NPs sizes were 15.94 nm, 18.08 nm, and 23.32 nm, respectively. FTIR confirmed Zn–O bonding with minimal organic residues, and UV-Vis spectroscopy revealed absorption edges between 345–380 nm, with band gap energies ranging from 3.08 to 3.17 eV respectively. Disc diffusion method was employed to evaluate the antibacterial performance. Agave-derived ZnO-NPs consistently produced the maximum inhibition zones (22.03 mm for E. coli; 19.06 mm for S. aureus at 50 μg/mL), followed by Chiku-derived ZnO-NPs and Soursop-derived ZnO-NPs. These results highlight the strong influence of nanoparticle size, morphology, and dispersion on biological efficacy. E. coli exhibited greater susceptibility than S. aureus, reflecting differences in their cell wall structures. This study introduces a novel sustainable pathway for nanoparticle synthesis, showing that natural extracts can produce antimicrobial NMs with strong activity. Beyond confirming their antibacterial efficacy, it underscores the role of green nanotechnology in minimizing environmental chemical burdens and advancing sustainable practices. Future directions include optimizing synthesis conditions, advancing toward scalable industrial production and extending evaluations against multidrug-resistant pathogens to unlock broader applications of Phytosynthesized ZnO-NPs in biomedical, pharmaceutical, food safety and sustainable material development domains.

https://orcid.org/0000-0003-1902-5550