Design, synthesis and optimization of silver nanoparticles using Azadirachta indica bark extract and its antibacterial application

The antibacterial effects of bio-inspired silver nanoparticles from Azadirachta indica bark were explored in this research work. Herein, the AgNPs were synthesized using aqueous extract of A. indica bark. The optimization of parameters was carried out using Box-Behnken Design using response surface methodology. The physicochemical characterizations of AgNPs were done by DLS, SEM, Zeta potential and FTIR. The DLS and SEM data revealed the average size of particles to be 76.35 nm and 30.6 nm, respectively. FTIR analysis has shown the involvement of conjugated alkenes in the biosynthesis and capping process. The antimicrobial activity was found to be increased in a dose dependent manner. Exploration of the mechanistic aspect of antibacterial activity suggested of cellular damages caused by AgNPs treatment due to membrane leakage. The binding of AgNPs with bacterial cell and cellular leakage were visualized by SEM. Further, in silico docking studies suggested of strong binding of BamA and PBP4 proteins found in E. coli and S. aureus, respectively, with β-sitosterol, salannin, nimbin etc. biomolecules found in the A. indica bark extract.