Comparative Biosynthesis, Physicochemical Characterization and Agronomic Application of Zinc Nanoparticles Produced through Bacterial and Plant-Mediated Green Synthesis Routes

Abstract

Green nanotechnology has emerged as an environmentally responsible alternative to conventional physicochemical routes for the fabrication of metal nanoparticles. The present investigation reports a comparative appraisal of bacterium-mediated and plant-mediated biosynthesis of zinc nanoparticles (ZnNPs), undertaken as part of a broader programme evaluating biogenic metal-nanoparticle production. An indigenous bacterial isolate recovered from industrial effluent, identified through 16S rRNA gene sequencing as Bacillus paramycoides, and an aqueous leaf extract of Moringa oleifera (drumstick) were separately employed as reducing and capping agents to convert zinc nitrate into ZnNPs. Nanoparticle formation was confirmed by a visible colour change and by the appearance of a characteristic surface plasmon resonance band in the ultraviolet-visible region. The particles were further examined by dynamic light scattering, zeta potential measurement, transmission electron microscopy, scanning electron microscopy and Fourier-transform infrared spectroscopy, and culture parameters governing microbial synthesis were optimized. The bacterium produced comparatively larger, more aggregated particles with markedly higher colloidal charge instability, whereas the plant extract yielded smaller, smoother, near-spherical particles with a narrower size range. Independent-samples statistical comparison confirmed that zeta potential differed significantly between the two synthesis routes, while particle-size parameters differed by a large practical margin without reaching conventional statistical significance, reflecting the constrained sample size typical of exploratory green-synthesis studies. Application of both ZnNP preparations to chilli (Capsicum annuum) seeds markedly improved germination percentage and seedling length relative to an untreated control, with the plant-derived nanoparticles conferring the greater agronomic benefit. These findings indicate that microbial and phytogenic synthesis routes are complementary rather than competing strategies: the bacterial route is advantageous where long-term colloidal stability is prioritised, whereas the phyto-synthetic route is preferable when fine particle size and growth-promoting bioactivity are the primary objectives. The study contributes baseline data toward the rational, application-driven selection of biological platforms for sustainable zinc nanoparticle manufacture.