Biogenic Synthesis of Au Nanoparticles Using Vascular Plants

The known metallophytes Brassica juncea (B juncea) and Medic:ago saliva (M saliva) were investigated for their ability to accumulate and sequester gold (Au) from aqueous solutions of KAuCl4 Once sequestered, some of the metal was stored as nanoparticles, throughout the epidermis, cortex, and vascular tissue for both species, but predominantly located in the xylem parenchyma cells Nanoparticle size distribution within the plant tissues was determined In general, particle sizes ranged between 2 nm to 2 mu m in B juncea and 2 nm to 1 mu m in M saliva and was location dependent, root located nanoparticles had similar size distributions in both species, whereas the distribution within above ground tissues differed between M saliva and B juncea, with B juncea showing a much broader range of particle sizes Au(0) nanoparticles were also formed ex vivo following contact between root exudates and an aqueous solution of KAuCl4 resulting in the reduction of Au(III) to Au(0) The largest proportion of particles was in the range 5-10 nm (B juncea) and 10-20 nm (M saliva) The mechanism of growth of Au(0) nanoparticles using live plants, both in vivo and ex vivo is consistent with Turkevich [Gold Bull 1985, 18 (3), 86-91], who suggested that the process of Au(0) particle formation involved the interplay of crystal nucleation, growth, and coagulation