Biogenic synthesis of silver nanoparticles using Azadirachta indica and Thevetia peruviana leaf extracts: Characterization, antibacterial analysis, machine learning-based toxicity, and In-Silico molecular docking studies for potential biomedical applications

Abstract

This study reports the eco-friendly synthesis of silver nanoparticles (Ag NPs) using leaf extracts of Azadirachta indica (Neem) and Thevetia peruviana (Kaner). Kaner-derived NPs exhibited superior properties with 24 nm crystallite size and 98.63 % purity, while Neem NPs showed irregular morphology (93.67 % Ag). The combined extract produced uniform, quasi-spherical particles (97.56 % Ag, 25–35 nm diameter), demonstrating synergistic stabilization. XRD analysis confirmed the presence of cubic/tetragonal crystal structures, and FTIR identified hydroxyl, carbonyl, and carboxyl groups as reducing/stabilizing agents. DLS measurements revealed hydrodynamic sizes of 80–180 nm with excellent colloidal stability for Kaner NPs (ζ-potential: −19.5 mV). Antibacterial assays showed concentration-dependent activity, with Kaner NPs demonstrating 12 mm inhibition zones against E. coli at 100 μg/mL and effectiveness against Bacillus subtilis. Molecular docking revealed interactions between the Ag atom and β-lactamase and MurA bacterial enzymes (binding energies: −0.74 to −0.93 kcal/mol), elucidating the antibacterial mechanism. Machine learning analysis (LightGBM) predicted dose-dependent behavior of 25–30 nm Ag-NPs across human cell lines, showing high LC50 values (375–850 µg/mL), ∼100 % viability, and negligible toxicity, confirming biocompatibility. These findings establish plant extract combinations as viable routes for the controlled synthesis of NPs with enhanced biomedical potential.