Microbial Synthesis of Noble Metal Nanoparticles using Metal-reducing Bacteria
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0942-W13-01
Microbial Synthesis of Noble Metal Nanoparticles using Metal-reducing Bacteria Yasuhiro Konishi, Kaori Ohno, Norizoh Saitoh, Toshiyuki Nomura, and Shinsuke Nagamine Dept. of Chemical Engineering, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka, 599-8531, Japan
ABSTRACT Microbial synthesis of gold nanoparticles was achieved at 25°C and pH 7 to 1 using the mesophilic bacterium Shewanella algae with H2 as the electron donor. The microbial synthesis of gold nanoparticles was a fast process: 1 mM AuCl4- ions was completely reduced to insoluble gold within 30 min. At pH 7, gold nanoparticles of 10-20 nm were synthesized in the periplasmic space of S. algae cells. When the solution pH was decreased to 1, gold nanoparticles of 50-500 nm were precipitated extracellularly. The solution pH was an important factor in controlling the morphology of biogenic gold particles and the location of gold deposition. INTRODUCTION Noble metal nanoparticles can be applied to a wide range of functions such as catalysis, optics and biosensing. Although chemical and physical synthetic routes for the production of noble metal nanoparticles have been extensively developed, another possibility is synthesis by bioreduction of noble metal ions using microorganisms. The microbial synthetic route to noble metal nanoparticles offers large savings in reductant and energy costs over conventional routes, and microbial synthesis is potentially attractive as an environmentally friendly method. There are several reports concerning the microbial synthesis of gold nanoparticles: intracellular synthesis by the actinomycete Rhodococcus sp. [1], the fungus Verticillium sp. [2] and the bacterium Acidithiobacillus thiooxidans [3]; extracellular synthesis by the fungus Fusarium oxysporum [4] and the actinomycete Thermomonospora sp. [5]; and intra- and extracellular synthesis by the cyanobacterium Plectonema boryanum [6]. Use of these microorganisms in gold precipitation has the disadvantage that the reduction of aqueous AuCl4ions is very slow, with complete reduction taking 2-30 days. In contrast, metal-reducing bacteria (e.g., Shewanella algae) were able to precipitate gold from about 1 mM aqueous HAuCl4 solutions at pH 7 within 30 min [7, 8]. Although the mesophile S. algae is a candidate microbe for rapid reduction of aqueous AuCl4- ions into insoluble gold, information is generally lacking concerning the characterization of the gold precipitates produced by S. algae. Moreover, a limited amount of information exists on the effect of operating conditions on the morphology and size of biogenic gold particles. This paper describes the intracellular and extracellular synthesis of gold nanoparticles by microbial reduction of aqueous AuCl4- ions using the metal-reducing bacterium S. algae at 25°C. The microbial synthesis of gold nanoparticles was studied to examine the effect of solution pH on the reduction rate and particle morphology.
EXPERIMENTAL DETAILS S. algae ATCC 51181 was obtained from the American Type Culture Collection (ATCC). Th
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