Green Synthesis of Silver Nanoparticles with Extracts from Kalanchoe fedtschenkoi: Characterization and Bioactivities

In this work, the hexane, chloroform, and methanol extracts from Kalanchoe fedtschenkoi were utilized to green-synthesize silver nanoparticles (Kf₁-, Kf₂-, and Kf₃-AgNPs). The Kf₁-, Kf₂-, and Kf₃-AgNPs were characterized by spectroscopy and microscopy techniques. The antibacterial activity of AgNPs was studied against bacteria strains, utilizing the microdilution assay. The DPPH and H₂O₂ assays were considered to assess the antioxidant activity of AgNPs. The results revealed that Kf₁-, Kf₂-, and Kf₃-AgNPs exhibit an average diameter of 39.9, 111, and 42 nm, respectively. The calculated ζ-potential of Kf₁-, Kf₂-, and Kf₃-AgNPs were -20.5, -10.6, and -7.9 mV, respectively. The UV-vis analysis of the three samples demonstrated characteristic absorption bands within the range of 350-450 nm, which confirmed the formation of AgNPs. The FTIR analysis of AgNPs exhibited a series of bands from 3500 to 750 cm^-1, related to the presence of extracts on their surfaces. SEM observations unveiled that Kf₁- and Kf₂-AgNPs adopted structural arrangements related to nano-popcorns and nanoflowers, whereas Kf₃-AgNPs were spherical in shape. It was determined that treatment with Kf₁-, Kf₂-, and Kf₃-AgNPs was demonstrated to inhibit the growth of E. coli, S. aureus, and P. aeruginosa in a dose-dependent manner (50-300 μg/mL). Within the same range, treatment with Kf₁-, Kf₂-, and Kf₃-AgNPs decreased the generation of DPPH (IC₅₀ 57.02-2.09 μg/mL) and H₂O₂ (IC₅₀ 3.15-3.45 μg/mL) radicals. This study highlights the importance of using inorganic nanomaterials to improve the biological performance of plant extracts as an efficient nanotechnological approach.