Plant-mediated green synthesis of silver nanoparticles using Amaranthus spinosus L. extract: antimicrobial, antioxidant and nano-seedling enhancement

Amaranthus spinosus is a medicinal plant rich in bioactive metabolites with potential biomedical applications. Our present study was designed to investigate Egyptian-grown A. spinosus as a sustainable biological source for silver nanoparticles (AgNPs) synthesis and to characterize the resulting nanoparticles and evaluate their biological properties. In the current investigation, AgNPs were successfully biosynthesized using the plant extract of A. spinosus as a natural stabilizing and reducing agent. Phytochemical screening proved the presence of phenol, flavonoids, saponins, and terpenoids in the plant extract. The synthesized AgNPs were evaluated by UV–Vis spectroscopy, FTIR, TEM, FE-SEM, EDX, and XRD analyses. Morphological observations revealed predominantly spherical and well-dispersed nanoparticles with nanoscale dimensions and crystalline cubic-phase geometry. Comparative analyses demonstrated that AgNPs displayed relatively higher antioxidant, antimicrobial, and cell viability assessment than the plant extract. The nanoparticles also revealed strong antibacterial activity against Acinetobacter baumannii , Enterobacter cloacae , Staphylococcus aureus , and Staphylococcus haemolyticus . Pronounced antifungal activity was also observed against Cochliobolus specifier , Fusarium oxysporum , and F usarium solani . The plant extract exhibited good cellular compatibility, with viability exceeding 100%, but the manufactured AgNPs showed severe cytotoxicity toward RAW264.7 macrophages, with cell viability falling to about 1% at both tested dosages (10 and 25 µg/mL). Furthermore, the AgNPs showed very little NO inhibition (0.74% and 2.85% at 10 and 25 µg/mL, respectively), which was linked to significant cytotoxicity and cannot be regarded as conclusive proof of anti-inflammatory efficacy. These results suggest that the plant extract has a better cytocompatibility profile than the synthetic AgNPs. To prove the plant extract’s anti-inflammatory efficacy, more research employing non-cytotoxic doses and additional inflammatory biomarkers is needed. Furthermore, AgNPs treatment significantly promoted seed germination and seedling growth of Hordeum vulgare in a concentration-dependent manner. These findings highlight the prospect of green-synthesized AgNPs as multifunctional nanomaterials for agricultural, pharmaceutical, and biomedical applications.