The mechanism of metal nanoparticle formation in plants: limits on accumulation
- 1.7k Downloads
Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal deposition and metal salt accumulation. This work describes the uptake of AgNO3, Na3Ag(S2O3)2, and Ag(NH3)2NO3 solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy (AAS) for total Ag, the quantity of reduction of AgI to Ag0 is reported. Transmission electron microscopy (TEM) showed Ag particles of 2–35 nm. The factors controlling the amount of silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited, of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals, is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode).
KeywordsSilver Nanoparticle Phytomining Phytoremediation XAS XANES EXAFS Nanobiotechnology
The authors wish to thank the Photon Factory Advanced Ring, Tsukuba, Japan, for beam time access under proposal 2008G207; Dr Masaharu Nomura and Garry Foran, Photon Factory, Tsukuba, for their assistance; NZ Synchrotron Group Limited for a travel grant; Prof Clive Davies for advice on hydroponics and Doug Hopcroft, Manawatu Microscopy Centre, for assistance with the TEM work.
- Aldrich MV, Gardea-Torresdey JL, Peralta-Videa JR, Parsons JG (2003) Uptake and reduction of Cr(VI) to Cr(III) by mesquite (Prosopis spp): chromate–plant interaction in hydroponics and solid media studied using XAS. Environ Sci Technol 37(9):1859–1864. doi: 10.1021/es0208916 PubMedCrossRefGoogle Scholar
- Aylward G, Findlay T (2002) SI chemical data, 5th edn. Wiley, MiltonGoogle Scholar
- Bard AJ, Parsons R, Jordan J (1985) Standard potentials in aqueous solution. Marcel Dekker, New YorkGoogle Scholar
- Bocquet ML, Michaelides A (2006) Exploring the catalytic activity of a noble metal: the Ag catalyzed ethylene epoxidation reaction. In: Grütter P, Hofer W, Rosei F (eds) Properties of single organic molecules on crystal surfaces. Imperial College Press, London, pp 389–424Google Scholar
- Brooks RR (1992) Noble metals and biological systems; their role in medicine, mineral exploration, and the environment. CRC, Boca RatonGoogle Scholar
- De La Rosa G, Peralta-Videa JR, Montes M, Parsons JG, Cano-Aguilera I, Gardea-Torresdey JL (2004) Cadmium uptake and translocation in tumbleweed (Salsola kali), a potential Cd-hyperaccumulator desert plant species: ICP/OES and XAS studies. Chemosphere 55(9):1159–1168. doi: 10.1016/j.chemosphere.2004.01.028 PubMedCrossRefGoogle Scholar
- Gardea-Torresdey J, Rodriguez E, Parsons JG, Peralta-Videa JR, Meitzner G, Cruz-Jimenez G (2005a) Use of ICP and XAS to determine the enhancement of gold phytoextraction by Chilopsis linearis using thiocyanate as a complexing agent. Anal Bioanal Chem 382(2):347–352. doi: 10.1007/s00216-004-2966-6 PubMedCrossRefGoogle Scholar
- Montes-Bayon M, Yanes EG, De Leon CP, Jayasimhulu K, Stalcup A, Shann J, Caruso JA (2002) Initial studies of selenium speciation in Brassica juncea by LC with ICPMS and ES-MS detection: an approach for phytoremediation studies. Anal Chem 74(1):107–113. doi: 10.1166/jbn.2007.041 PubMedCrossRefGoogle Scholar
- Nomura M, Koike Y, Sato M, Koyama A, Inada Y, Asakura K (2007) A new XAFS beamline NWIOA at the photon factory. In: Hedman B, Pianetta P (eds) XAFS13—13th international conference, 882 (X-ray absorption fine structure) AIP conference proceedingsGoogle Scholar