Coalescence of Nanoclusters and Formation of Submicron Crystallites Assisted by Lactobacillus Stra

Coalescence of Nanoclusters and Formation of Submicron Crystallites Assisted by Lactobacillus Stra

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Coalescence of Nanoclusters and Formation of Submicron Crystallites Assisted by Lactobacillus Strains Binoj Nair and T. Pradeep* Department of Chemistry and Regional Sophisticated Instrumentation Centre, Indian Institute of Technology, Madras 600 036, India Received April 6, 2002; Revised Manuscript Received May 13, 2002 ABSTRACT: Lactobacillus strains, common in buttermilk, assist the growth of gold, silver, and gold - silver alloy crystals of submicron dimensions upon exposure to the precursor ions. Several well-defined crystal morphologies are observed. Crystal growth occurs by the coalescence of clusters, and tens of crystals are found within the bacterial contour. Crystal growth does not affect the viability of the bacteria. Crystals are presumably nucleated through nanoclusters, which are formed within as well as transported into the bacteria. Biomass with the crystals can be harvested completely. Results point to potential applications in analytical chemistry, nanotechnology, medicine, and metal ion recovery. Coalescence appears to be a route by which surface area of the crystal is reduced so that it can be effectively protected to avoid biological damage. Introduction Tomorrow’s technology is going to depend on nano- structured metals 1 and semiconductors. 2 It is predicted that the impact of this technology will be felt greatly at the interface of chemistry and biology. 3 The desire to synthesize materials using efficient and green chemistry approaches is considerable, which has led to the use of microorganisms. Although efforts directed toward nano- materials are recent, metal ion interaction with prokary- otic species has been one of the focal points of research for a long time. 4 Bacteria have been known to enrich ions, 5 synthesize magnetite crystals, 5,6 reduce Ag + into metal particles, 7 form nanoparticles 5,8 as well as octa- hedral gold 9 containing S and P, and recently, prepare ceramic to metal composites 10 (cermets). Formation of minerals by unicellular and multicellular organisms has long been recognized; the synthesis of siliceous materi- als 11 by diatoms and the preparation of gypsum and calcium carbonate 12 by S-layer bacteria are some of the examples. Single-crystalline semiconducting particles such as CdS have been synthesized in algae. 13 The most recent addition into this biosynthesis approach is the reduction of gold and silver by fungi. 14 Variety and diversity of this chemistry suggest nu- merous possibilities with other, more common micro- organisms. Herein we report the growth of gold, silver, and gold - silver alloy crystals with well-defined mor- phologies assisted by most common Lactobacillus strains found in buttermilk, when exposed to appropriate ions. Accumulation of metals occurs to such an extent that
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Coalescence of Nanoclusters and Formation of Submicron Crystallites Assisted by Lactobacillus Stra

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