Plant mediated synthesis of silver nanoparticles and their biological applications

The green synthesis of nanoparticles using plants and their extracts is considered as a representative approach in material synthesis for environmental benignity. Numerous metal nanoparticles with potential bioactivities have been prepared based on plant extracts. In this paper, we report an eco-friendly technique for the preparation of silver nanoparticles using plant extract of  Justicia diffusa  Willd. and the evaluation of their antioxidant, antidiabetic, and  cytotoxicity  activities. UV-visible spectroscopy, transmission electron microscopy, scanning electron microscopy and atomic force microscopy analysis were used to characterize the morphology and size of silver nanoparticles. The stability of silver nanoparticles toward acidity, alkalinity, salinity and temperature showed that they remained stable at room temperature for more than two months. UV–vis spectrum of the aqueous medium containing silver nanoparticles showed an absorption peak at around 420 nm. The scanning electron microscopy analysis of the silver nanoparticles showed that they have a uniform spherical shape with an average size in the range of 40–78 nm. This was confirmed by transmission electron microscopy analysis which showed an average size of about 50 nm. Thus green system showed better capping and stabilizing agent for the fine particles. Further 1-diphenyl-2-picrylhydrazl radical in Justicia diffusa mediated silver nanoparticles showed a maximum activity of 67% at concentration of 200 μg/mL. Hydrogen peroxide scavenging assay in Justicia diffusa  mediated silver nanoparticles showed a maximum activity of 89% at concentration of 200 μg/mL. Reducing power of Justicia diffusa  silver nanoparticles exhibited a higher activity of 246 μg/mL at concentration of 200 μg/mL. These NPs showed the cytotoxic effects against brine shrimp ( Artemia salina ) Nauplii with a value of 35% and LD value of 271 μg/mL. The AgNPs synthesized using  Justicia diffusa  Willd.  extract also show remarkable antidiabetic activities. KEY WORDS : Justicia diffusa , Nanoparticles, TEM, SEM, AFM Bull. Chem. Soc. Ethiop. 2018 , 32(3), 469-479. DOI: https://dx.doi.org/10.4314/bcse.v32i3.6