Cyanobacteria mediated green synthesis of gold-silver nanoalloy

Green synthesis is a significant process for non-toxic metal nanoparticle production employing plant materials. In the present investigation we reported an environmentally friendly method for gold-silver nano-alloy biosynthesis using a cyanobacterial strain, Lyngbya majuscula as bio-reagent. On exposure of Lyngbya thallus to equimolar solution of gold and silver (1 mM, pH 4) for 72 hrs and subsequent pink coloration of the experimental biomass indicated the nanoparticle synthesis. Extracted nanoparticles showed a distinct single plasmon band at 481 nm and further EDX analysis confirmed the presence of both the metals Au and Ag in nano-alloy form. It was also observed from TEM study that all the synthesized particles were spherical in nature with a size range of ~5-25 nm. The SEM pictures of the metal treated biomass confirmed the intra and extracellular nano-alloy formation. The XRD analysis of particle loaded biomass revealed that the 2θ values appeared at 38.2°, 44.5°, 64.8°and 77.8° that were indexed at (111), (200), (220) and (311) lattice planes. Presence of different functional groups viz. N-H, C=C, C–O, C=O on the surface of nanoparticles were recorded by FTIR. Overall, this technique requires low energy and less manufacturing cost for metal alloy biosynthesis.