Eco-friendly silver nanoparticles from neem extracts: a dual approach to heavy metal sensing and antimicrobial applications

This work investigates the green synthesis of silver nanoparticles (AgNPs) using mixed aqueous extracts of Azadirachta indica leaves and roots as natural reducing and stabilizing agents. The synthesis was optimized by varying extract concentration, pH, and temperature, and nanoparticle formation was confirmed by UV-Vis spectroscopy showing a characteristic surface plasmon resonance between 350 and 450 nm. Structural and morphological analyses {X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier-Transform Infrared (FT-IR), particle size analysis} revealed predominantly crystalline, spherical AgNPs capped by phytochemicals like flavonoids, phenols, amide- and carbonyl-containing compounds. The phytochemical profile of the extract was further validated by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. The biosynthesized AgNPs exhibited strong colorimetric sensing capability for heavy metals, showing noticeable spectral and visible color changes particularly in the presence of Hg²⁺, Pb²⁺, and Cd²⁺ ions. Antibacterial evaluation indicated significant inhibitory activity against Staphylococcus aureus (33 ± 0.13 mm) and Escherichia coli (45 ± 0.21 mm), outperforming standard gentamycin controls. These findings highlight neem-derived AgNPs as low-cost, eco-friendly nanomaterials with dual applications in environmental monitoring of heavy metals and antimicrobial therapy.