Journal of Microbiology and Biotechnology Research Scholars Research Library J. Microbiol. Biotech. Res., 2012, 2 (4):485-492 (http://scholarsresearchlibrary.com/archive.html) ISSN : 2231 –3168 CODEN (USA) : JMBRB4 485 Available online at www.scholarsresearchlibrary.com Biogenic Fabrication of Gold Nanoparticles using Halomonas salina Ritu Shah, Goldie Oza, Sunil Pandey and Madhuri Sharon* N. S. N. Research Centre for Nanotechnology and Bionanotechnology, Jambhul Phata, Ambernath (W) 421 505, Maharashtra, India _____________________________________________________________________________________________ ABSTRACT Use of microorganisms as novel and eco-friendly approach for biosynthesis of gold nanoparticles by exploiting the reducing and thermodynamically efficient molecular mechanisms of Halomonas salina is reported in the present work. The biosynthesis was significantly impacted by both pH and temperature of the reactants. At lower temperature (30ºC) the optimum parameters were pH 9 and 100 ppm of aurochlorate salt for fabrication of thermodynamically stable isotropic nanostructures. Whereas under same conditions pH 4, resulted into anisotropic orchestration of biogenically derived gold nanoparticles of size 30 - 100 nm. The stability of gold nanoparticles was also studied using 5 M NaCl salt. The contribution of nitrate reductase in reducing the gold ions to gold nanoparticles was assayed biochemically. The nitrate reductase activity got drastically reduced from 1.21 μmole/min/ml supernatant to 0.23 μmole/min/ml supernatant; after biogenic fabrication of gold nanoparticles. The morphology and the crystal structure of the gold nanoparticles (GNP) were characterized using electron microscopy and X Ray Diffraction respectively. Keywords: Halomonas salina, Biosynthesis, Gold nanoparticles, Surface Plasmon Resonance, Stability, Nitrate reductase. _____________________________________________________________________________________________ INTRODUCTION The bio-based protocols for synthesis of nanometals are both environmentally and economically green as they are based on green chemistry principles and are simple and relatively inexpensive. The chemical methods available are often expensive, utilize toxic chemicals and are comparatively complicated. Certainly such methods are not eco- friendly and hence cleaner, cheaper, green processes that do not employ toxic chemicals for the synthesis of nanoparticles have to be devised. Material scientists are constantly striving hard for synthesizing plethora of different methods for synthesis of gold nanoparticles of uniform size, shape, composition and mono-dispersity. There is overwhelming need for green synthesis of environmental friendly method of nanoparticle synthesis, thus generating negligible amounts of toxic chemicals. Thus, to refrain from catastrophic toxic chemical synthetic strategies, material scientists have turned to organisms for inspiration. The optoelectronic and physicochemical properties of nanoscale matter are size- and shape-dependent [1–3]. So the synthesis of gold nanoparticles of different sizes and shapes is of great importance for their applications in optical devices, electronics, biotechnologies and catalysis [4–6]. Conventional synthetic methods of gold nanoparticles have involved a number of chemical methods [7–10]. There is an increasing pressure to develop clean, nontoxic and environmentally benign synthetic technologies. Microbial resistance against heavy metal ions has been exploited for biological metal recovery via reduction of the metal ions or formation of metal sulfides [11]. So the attractive procedure is using microorganisms such as bacteria and fungi to synthesize gold nanoparticles. An earlier study found that Bacillus subtilis 168 [12]