Green Synthesis and Characterization of Plant Leaf Extract–Mediated Silver Nanoparticles and Their Antimicrobial Activity

This study details the eco-friendly synthesis of silver nanoparticles utilizing Azadirachta indica (Neem) leaf extracts, which function as both stabilizing and reducing agents for the transformation of silver ions. Phytochemical constituents, including flavonoids, phenolics, and alkaloids, facilitate this metal ion reduction, providing a sustainable alternative to conventional chemical methods. To ensure reproducibility and elucidate the specific biomolecules involved, phytochemical profiling was conducted via HPLC/GC-MS, identifying quercetin and rutin as primary capping agents. Analytical characterization via UV-visible spectroscopy and field-emission scanning electron microscopy confirms the formation of stable, spherical nanoparticles with dimensions often falling within the sub-100 nm range. Dynamic Light Scattering (DLS) confirmed an average hydrodynamic size of 68 nm with a Polydispersity Index (PDI) of 0.18, while Zeta potential measurements (-34.5 mV) and pH/ionic strength stress tests validated long-term colloidal stability. Furthermore, Fourier-transform infrared spectroscopy analysis elucidates the specific functional groups responsible for the capping and long-term stabilization of these biogenic nanostructures. The surface plasmon resonance observed via UV-vis spectroscopy typically yields a characteristic absorption peak between 410 and 450 nm, confirming the successful conversion of silver ions into stable colloidal nanoparticles. In addition to their structural verification, these biogenic silver nanoparticles have demonstrated potent bactericidal efficacy against both Gram-positive and Gram-negative pathogens, such as Escherichia coli and Staphylococcus aureus. Quantitative evaluation via micro-dilution established robust Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) values of 12.5 µg/mL and 25.0 µg/mL, respectively, outperforming chemical AgNP controls. Furthermore, quantitative evaluation of these inhibition zones suggests that the interaction between the leaf-derived organic capping agents and the bacterial cell wall enhances the bioactivity of the particles. Mechanistic ROS and membrane leakage assays confirmed significant cellular disruption, while MTT cytotoxicity assays on HEK-293 mammalian cells (>85% viability) established a strong safety profile for clinical applications.

Green synthesis, silver nanoparticles, Azadirachta indica, antimicrobial activity

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