Hydrothermal Assisted Synthesis and Biological Evaluation of Biogenic Silver Nanoparticles

Abstract We report on hydrothermal synthesis of biogenic silver nanoparticles (AgNPs) using aqueous leaf extract of Alchornea laxiflora for threefold applications in antibacterial screening against Escherichia coli and Staphylococcus aureus , tyrosinase inhibition of mushroom tyrosine enzymes with 3,4-dihydroxyphenylalanine as a substrate and photocatalytic degradation of malachite green dye. The mode of action for the tyrosinase application and kinetics of both the tyrosinase and photocatalytic activities were provided. The localized surface resonance bands of the AgNPs were observed within the range of 424 – 435 nm from the electronic spectral analysis. Fourier transform-infrared studies reveal the functional groups of plant metabolites such as phenolic compounds and amines on the nanoparticles. The Energy Dispersive X-ray result reveals the presence of silver and other elemental compositions from the plant extract. X-ray diffraction result showed a face-centred cubic crystalline structure for the AgNPs. The SEM analyses reveal that the nanoparticles are spherical in shape with average size range of 20-52 nm. The AgNPs exhibited a dose dependent tyrosinase inhibition activity with IC 50 of 20.83 µg/ml and a competitive mode of inhibition. The results of photocatalytic degradation of malachite green dye depicted rapid photo inspired degradation of 86 % in less than a min and at reaction rate of 0.136 min -1 . The silver nanoparticles showed enhanced antibacterial activities compared to the precursors: silver nitrate and aqueous extract of Alchornea laxiflora .