Silver and gold nanoparticles in plants: sites for the reduction to metal

Abstract

Induced formation of metal nanoparticles in living plants is poorly understood. The sites for the reduction of Ag(+) and Au(3+) to Ag(0) and Au(0) metal nanoparticles in vivo in plants were investigated in order to better understand the mechanism of the reduction processes. Brassica juncea was grown hydroponically, followed by growth in solutions of AgNO(3), [Ag(NH(3))(2)]NO(3) or HAuCl(4). Harvested plants were sectioned and studied by transmission electron microscopy. Total metal content was analysed by atomic absorption spectroscopy. The chemical state of the metals was determined by X-ray absorption spectroscopy. Nanoparticles of Ag(0) and Au(0) were found in leaves, stem, roots and cell walls of the plants at a concentration of 0.40% Ag and 0.44% Au in the leaves. Particles which were approximately spherical were formed with sizes of 2-100 nm. The sites of the most abundant reduction of metal salts to nanoparticles were the chloroplasts, regions of high reducing sugar (glucose and fructose) content. We propose that these sugars are responsible for the reduction of these metals and other metal salts with reduction potentials over +0.16 V and that the amount of reducing sugar present or produced determines the quantity of metal nanoparticles that may be formed.

Synthesis of metal nanoparticles in living plants

“…On the contrary, little has been understood about this process in living plants. Beattie and Haverkamp (2011) recently investigated the location of Au and AgNPs formation within the tissues of Brassica juncea with the aim of clarifying the mechanisms of NPs formation. A couple of experimental observations were recorded.…”

Biosynthesis of gold nanoparticles using chloroplasts

“…When Shama et al 23 bioreduced Au 3+ to Au 0 nanoparticles in plants, they discovered an interesting phenomena that many GNPs surrounded organelles. Additionally, Beattie and Haverkamp 24 demonstrated that the site of the most abundant reduction of Au 3+ metal salts to Au 0 nanoparticles in plants were chloroplasts. This prompted the authors of the present paper to investigate the possibility of biosynthesizing GNPs using chloroplasts as biological templates.…”

The ways to increase efficiency of soil bioremediation

“…When research had been conducted on bioreduced Au 3+ to Au 0 nanoparticles in plants by Sharma et al [80], they discovered that many gold nanoparticles surrounded organelles. Moreover, Beattie and Haverkamp [81] demonstrated that chloroplasts were the site of the most abundant reduction of Au 3+ salts to Au 0 nanoparticles in plants. This prompted the authors to investigate the possibility of biosynthesized gold nanoparticles using chloroplasts as biological templates and the chloroplasts acted in dual roles, ie as reducing agents and stabilizers in the course of the formation of gold nanoparticles [82].…”