Phyto-Fabrication of Zinc Oxide Nanoparticles Using Senna occidentalis: Comprehensive Characterization, Phytochemical Profiling, and Antimicrobial Assessment

This study reports the green synthesis of ZnONPs using aqueous leaf extract of Senna occidentalis, a phytochemically rich medicinal plant. The synthesized nanoparticles were characterized using UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), energy-dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). UV-visible analysis confirmed nanoparticle formation through a characteristic absorption peak at 393 nm with 13.85% intensity. TEM micrographs revealed predominantly spherical and aggregated ZnONPs with an average size of 93 nm. EDS analysis confirmed the presence of elemental zinc through distinct peaks at 1.0, 8.8, and 9.8 keV. FTIR spectra identified a prominent O–H stretching vibration at 3493 cm⁻¹, indicating the presence of polyphenolic compounds involved in nanoparticle stabilization. The antimicrobial activity of both ZnONPs and doped ZnO/AgNPs was evaluated via agar well diffusion assays against clinical strains of Escherichia coli, Staphylococcus aureus, and Streptococcus pyogenes. The doped nanoparticles demonstrated enhanced and species-selective antimicrobial effects, particularly against S. pyogenes, suggesting possible differential mechanisms of bacterial inhibition. This research highlights the viability of Senna occidentalis-mediated biosynthesis of ZnONPs as a scalable, eco-conscious approach to nanoparticle production. In addition to the antimicrobial results, the biosynthesis route employed here aligns with the principles of green chemistry, eliminating the need for hazardous reducing agents and minimizing energy consumption. The rich phytochemical profile of S. occidentalis, including flavonoids, tannins, saponins, and phenolic acids, not only facilitates the reduction of zinc salts into ZnONPs but also contributes to the stabilization and capping of the nanoparticles, enhancing their colloidal stability and bioactivity. Furthermore, doping ZnONPs with silver particles resulted in synergistic effects, likely due to the combined mechanisms of reactive oxygen species generation, membrane disruption, and interference with essential metabolic pathways in bacteria. The observed enhanced antimicrobial effect of doped ZnO/AgNPs over pure ZnONPs may also be attributed to improved surface reactivity and increased particle–cell contact, which can accelerate bacterial cell wall penetration. Considering the urgent need for alternative antimicrobial strategies, such biosynthesized nanomaterials offer a sustainable route toward developing next-generation therapeutics. Future studies should also focus on shelf-life assessment, scalability trials, and potential integration with other natural biocidal agents to broaden their application scope in medical, agricultural, and environmental sectors. The eco-friendly synthesis described in this work presents several advantages over conventional chemical and physical methods of nanoparticle production. By harnessing the phytochemical constituents of S. occidentalis, the process achieves dual functionality—acting both as a reducing and capping agent—while avoiding toxic solvents or high-energy inputs. This approach not only reduces the overall cost but also minimizes potential environmental hazards. Moreover, the resulting ZnONPs and ZnO/AgNPs exhibit promising bioactivity that can be tailored for specific therapeutic applications through controlled synthesis parameters. Such versatility enhances their potential use in topical antimicrobial formulations, medical device coatings, and targeted drug delivery systems. In addition, their biocompatibility, once validated through in vitro and in vivo studies, could support broader applications in regenerative medicine. Overall, these findings contribute to advancing sustainable nanotechnology in addressing the growing problem of multidrug-resistant infections. These advancements reinforce green-synthesized nanoparticles in future biomedical and pharmaceutical innovations.