BIOSYNTHESIS AND CHARACTERIZATION OF SILVER NANOPARTICLES FROM AZADIRACHTA INDICA LEAF EXTRACT AND THEIR ANTIMICROBIAL AND ANTIOXIDANT POTENTIAL

Abstract

Background: Green synthesis of silver nanoparticles using medicinal plants has emerged as an environmentally friendly and sustainable approach for developing novel antimicrobial agents. Azadirachta indica (Neem) is a well-known medicinal plant rich in bioactive phytochemicals that possess diverse therapeutic properties and can act as natural reducing and stabilizing agents during nanoparticle synthesis. Objective: The present study aimed to biosynthesize silver nanoparticles (AgNPs) using Azadirachta indica leaf extract and evaluate their phytochemical composition, FTIR characterization, antioxidant potential, and antimicrobial efficacy against selected pathogenic microorganisms. Methods: Fresh Neem leaf extract was used for the green synthesis of AgNPs using 1 mM silver nitrate solution. Preliminary phytochemical screening was performed using standard qualitative methods. The synthesized nanoparticles were characterized by Fourier Transform Infrared (FTIR) spectroscopy to identify the functional groups involved in nanoparticle synthesis and stabilization. Antioxidant activity was evaluated using the DPPH free radical scavenging assay, while antimicrobial activity was assessed by the agar well diffusion method against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis. Results: Preliminary phytochemical screening confirmed the presence of phenolics, flavonoids, tannins, alkaloids, terpenoids, and saponins in the Neem leaf extract. FTIR analysis revealed characteristic absorption peaks at 3421, 2926, 1634, 1382, and 1084 cm⁻¹, corresponding to hydroxyl (–OH), aliphatic C–H, carbonyl (C=O), amine (C–N), and C–O functional groups, respectively, indicating their role in the reduction and stabilization of silver nanoparticles. The synthesized AgNPs exhibited potent antioxidant activity with an IC₅₀ value of 41.8 µg/mL. The highest antibacterial activity was observed against Pseudomonas aeruginosa (24.8 ± 0.6 mm), followed by Escherichia coli (23.5 ± 0.5 mm), Staphylococcus aureus (22.3 ± 0.4 mm), and Bacillus subtilis (20.9 ± 0.7 mm), which was significantly greater than that of the crude leaf extract (p < 0.05). Conclusion: The FTIR findings confirmed the involvement of bioactive phytochemicals in the biosynthesis and stabilization of silver nanoparticles. The biosynthesized AgNPs demonstrated significant antioxidant and broad-spectrum antimicrobial activities, suggesting their potential application as eco-friendly nanomaterials for pharmaceutical and biomedical applications.