Formation and Growth of Au Nanoparticles inside Live Alfalfa Plants J. L. Gardea-Torresdey, † J. G. Parsons, † E. Gomez, † J. Peralta-Videa, † H. E. Troiani, ‡ P. Santiago, ‡,§ and M. Jose Yacaman* ,‡,| Department of Chemistry, and EnVironmental Science and Engineering Ph.D. Program, UniVersity of Texas, El Paso, Texas 79968, CNM, Texas Materials Institute and Chemical Engineering Department, UniVersity of Texas, Austin, Texas 78712, and Instituto Nacional de InVestigaciones Nucleares, ININ, Mexico, and Instituto de Fisica, UNAM, Apdo 20-364, Mexico 20 DF Received November 21, 2001; Revised Manuscript Received January 9, 2002 ABSTRACT In modern nanotechnology one of the most exciting areas is the interaction between inorganic quantum dots and biological structures. For instance gold clusters surrounded by a shell of organic ligands covalently attach to proteins or other biological substances and can be used for labeling in structural biology. In the present report we show the possibility of using live plants for the fabrication of nanoparticles. Alfalfa plants were grown in an AuCl 4 rich environment. The absorption of Au metal by the plants was confirmed by X-ray absorption studies (XAS), and transmission electron microscopy (TEM). Atomic resolution analysis confirmed the nucleation and growth of Au nanoparticles inside the plant and that the Au nanoparticles are in a crystalline state. Images also showed defects such as twins in the crystal structure, and in some cases icosahedral nanoparticles were found. X-ray EDS studies corroborated that the nanoparticles are pure gold. This is the first report on the formation of gold nanoparticles by living plants and opens up new and exciting ways to fabricate nanoparticles. It shows how it is possible to link materials science and biotechnology in the new emerging field of nanobiotechnology. The field of nanotechnology is one of the most active areas of research in modern materials science. New applications of nanoparticles and nanomaterials are emerging rapidly. 1-3 The synthesis of nanoparticles and their self-assembly is a cornerstone of nanotechnology. New methods to manufacture nanoparticles are constantly being studied and developed. Additionally, environmental metal contamination byproducts associated with metal production has become a great concern for environmental reasons. 4 An example is the processing of valuable metal ores, which provides a route for toxic compounds to enter the environment. A paradigm of this is the current technology to extract gold, in which cyanide is used to release gold from the ore into a solution as gold cyanide [AuCN 2 ]. Currently, the AuCN 2 is still absorbed onto activated carbon and is subsequently stripped from the carbon followed by electrochemical reduction to gold(0), which is a very expensive process. Recently, it has been shown that several types of inactivated biomasses and living organisms have the ability to remove high concentrations of gold(III) from solution and to reduce gold(III) to gold(0). 5-7 These studies provide the possibility of an environmentally friendly method to remediate mining wastes. Although it is well-known that inactivated biological systems interact with metal ions, the connection between metal ions and biological systems is more in depth. As is well-known, many elements at trace concentrations are essential for plant growth and propagation; however, these same elements at higher concentrations are toxic to some plants. More specifically it has been shown that many bacteria and plants can actively uptake and bioreduce metal ions from soils and solutions. A well-known example of bioreduction and nanoparticle production is the magnetostatic bacteria that can synthesize magnetic nanoparticles. 2 Another example of nanoparticle production using inactivated alfalfa biomass has shown that biomass can reduce gold(III) ions in solution to gold(0) nanoparticles. 8 The use of inactivated biomass to recover metal ions from solution has been studied extensively. The possibility of using live bacteria for the remediation of metal-contaminated waters has shown the bacterial production of silver-carbon composite materials. Also, the formation of surface trapping of nanoparticles by fungus has been reported. 3,9 These are examples that link biotechnology and material science (nanobiotechnology). 3,9,10 * To whom correspondence should be addressed. E-mail: yacaman@ che.utexas.ed. ² Department of Chemistry and Environmental Science and Engineering Ph.D. Program at the University of Texas. ‡ CNM, Texas Materials Institute and Chemical Engineering Department. § Instituto Nacional de Investigaciones Nucleares. | Instituto de Fisica. NANO LETTERS xxxx Vol. 0, No. 0 A-E 10.1021/nl015673+ CCC: $22.00 © xxxx American Chemical Society PAGE EST: 4.8 Published on Web 00/00/0000