Eco-Friendly Synthesis of Silver Nanoparticles Using Neem and Eucalyptus Leaf Extracts: Characterization and Antimicrobial Efficacy Against Pathogenic Microbes

Silver nanoparticles are widely recognized for their potent antimicrobial properties. Conventional synthesis methods rely on toxic chemicals and high energy input, posing environmental and biomedical concerns. This study presents an eco-friendly, cost-effective synthesis of AgNPs using aqueous leaf extracts of Neem (Azadirachta indica) and Eucalyptus (Eucalyptus globulus) as reducing and stabilizing agents. Optimization of synthesis parameters, including extract-to-silver nitrate ratio, temperature, and incubation time, yielded stable, uniformly dispersed nanoparticles. Formation of AgNPs was confirmed visually and by UV–Vis spectroscopy (SPR peak 412–425 nm). TEM and SEM revealed spherical particles (Neem: 15–35 nm; Eucalyptus: 10–25 nm). XRD confirmed the crystalline face-centered cubic structure, while FTIR analysis indicated functional groups (hydroxyl, carbonyl, ether) involved in capping. Zeta potential analysis demonstrated greater colloidal stability for Eucalyptus-mediated AgNPs (−30.3 mV) compared to Neem (−22.1 mV). Antimicrobial assays against Gram-positive (Staphylococcus aureus, Bacillus subtilis), Gram-negative (Escherichia coli, Pseudomonas aeruginosa), and Candida albicans revealed significant activity of both Neem- and Eucalyptus-AgNPs, with Eucalyptus showing superior efficacy. One-way ANOVA and Tukey post-hoc analysis confirmed statistically significant differences (p < 0.001). This study demonstrates that green synthesis using plant extracts produces stable, biofunctional AgNPs with broad-spectrum antimicrobial activity, highlighting their potential for pharmaceutical applications such as wound dressings and topical antimicrobials.