Synthesis of silver nanoparticles using natural pigments extracted from Alfalfa leaves and its use for antimicrobial activity

The synthesis and characterization of silver nanoparticles (AgNPs) using natural pigments from plants as reducing agents is presented in this study. The natural pigments were extracted from Alfalfa leaves. The reduction reaction was investigated by UV-Vis and FTIR analyses. The synthesized AgNPs were characterized by UV-Vis, XRD, TEM, and DLS. UV-Vis analysis revealed that AgNPs were produced with a persistent plasmonic absorption peak at about 418 nm accompanied by consumption of pigments. The reduction is suggested to occur, mainly, by chlorophyll a and carotenes. Characterization revealed pure synthesized AgNPs with an average particle size of 25 nm. In an interesting novel experiment, the progress of reduction reaction was traced at the interface between reacting phases under UV illumination making use of fluorescence of both chlorophylls and formed Ag nano-clusters (AgNCs). The enrollment of chlorophylls in reduction was suggested depending on FTIR and fluorescence analyses. The synthesized AgNPs possessed a superior antimicrobial activity towards Staphylococcus aureus ATCC 29213; 24.0 mm ZOI, followed by Escherichia coli ATCC 25922; 17.0 mm ZOI. In addition, AgNPs were a strong antifungal agent against Candida albicans ATCC 10231; 26.0 mm ZOI.