Green Synthesis of Silver Nanoparticles: Their Characterization, Antimicrobial, Antioxidant Activity and Nanogel Formulation

This study investigates an efficient and sustainable route of preparing Ag nanoparticles (NPs) using 1–5 mmol/L aqueous silver nitrate with leaf extracts of five plants—Musa balbisiana (banana), Azadiracta indica (neem), Ricinus communis (castor-oil plant), Tridax procumbens (tridax), and Cardiospermum halicacabum (balloon vine) for their wide availability. These synthesized nanoparticles were characterized with the help of ultraviolet (UV)–visible (Vis) spectrophotometer. The peaks were observed in 418–493 nm. For M. balbisiana, A. indica, R. communis, and C. halicacabum, the average size of nanoparticles was in the range of 90–100 nm. For T. procumbens, it was 39–60 nm as determined by dynamic light scattering. Energy dispersive X-ray spectroscopy analysis showed the peak in silver region confirming presence of elemental silver. Field emission scanning electron microscopy showed that the particles were of a spherical shape in M. balbisiana sample with an average size of 33.87 nm as well as in T. procumbents sample with an average size of 28.512 nm. Ag NPs showed effective antibacterial and antifungal activity against representative pathogens of bacteria and fungi. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity of Ag NPs was found to be in the range of 8.9%–78.86%. H₂O₂ radical scavenging activity was recorded in the range of 6.036%–57.342%. The nanogel was prepared from synthesized Ag NPs, and its properties like viscosity and stability were evaluated. The results confirmed that this protocol is a simple, rapid, one-step, eco-friendly, nontoxic, and alternative conventional physical/chemical method.