Biological synthesis of metallic nanoparticles.

Biological synthesis of metal nanoparticles by microbes.

Nanotechnology is a new and emerging technology with wealth of applications. It involves the synthesis and application of materials having one of the dimensions in the range of 1-100 nm. A wide variety of physico-chemical approaches are being used these days for the synthesis of nanoparticles (NPs). However, biogenic reduction of metal precursors to produce corresponding NPs is eco-friendly, less expensive, free of chemical contaminants for medical and biological applications where purity of NPs is of major concern. Biogenic reduction is a "Bottom Up" approach similar to chemical reduction where a reducing agent is replaced by extract of a natural products with inherent stabilizing, growth terminating and capping properties. Furthermore, the nature of biological entities in different concentrations in combination with reducing organic agents influence the size and shape of NPs. Present review focuses on microbes or plants based green synthesis of Ag, Au, Cu, Fe, Pd, Ru, PbS, CdS, CuO, CeO2, Fe3O4, TiO2, and ZnO NPs and their potential applications.

Green synthesis of nanoparticles and its potential application.

Recent advances in nanoscience and nanotechnology have also led to the development of novel nanomaterials, which ultimately increase potential health and environmental hazards. Interest in developing environmentally benign procedures for the synthesis of metallic nanoparticles has been increased. The purpose is to minimize the negative impacts of synthetic procedures, their accompanying chemicals and derivative compounds. The exploitation of different biomaterials for the synthesis of nanoparticles is considered a valuable approach in green nanotechnology. Biological resources such as bacteria, algae fungi and plants have been used for the production of low-cost, energy-efficient, and nontoxic environmental friendly metallic nanoparticles. This review provides an overview of various reports of green synthesised zero valent metallic iron (ZVMI) and iron oxide (Fe₂O₃/Fe₃O₄) nanoparticles (NPs) and highlights their substantial applications in environmental pollution control. This review also summarizes the ecotoxicological impacts of green synthesised iron nanoparticles opposed to non-green synthesised iron nanoparticles.

Green Synthesis of Iron Nanoparticles and Their Environmental Applications and Implications

Large-scale hydrophilic Fe 3O 4 nanoparticles (NPs) were prepared in the presence of citrate and sodium nitrate via a facile method. The Fe 3O 4 NPs are quite stable and can be freely dispersed in water. The as-prepared magnetic nanoparticle solution can be stable for more than 1 month. The mean diameter of the Fe 3O 4 NPs can be controlled in the range of ∼20 to ∼40 nm in mean diameter. The NPs show superparamagnetic properties with a relatively high saturation magnetization moment 58 emu/mg at room temperature. Furthermore, a possible formation mechanism is proposed to explain why the magnetic nanoparticles are very well soluble in water.

Large-Scale Fe3O4 Nanoparticles Soluble in Water Synthesized by a Facile Method

The synthesis of iron oxide nanoparticles of the predominantly magnetite phase by the reaction of aqueous iron complexes with the bacterium, Actinobacter spp., is described. This reaction occurs at room temperature and under aerobic conditions, resulting in the formation of superparamagnetic magnetite.

Bacterial aerobic synthesis of nanocrystalline magnetite.

Molecular analyses of microbial diversity associated with the Lonar soda lake in India: an impact crater in a basalt area.

The diversity of methanogenic archaea in enrichment cultures established from the sediments of Lonar Lake (India), a soda lake having pH ≈ 10, was investigated using 16S rDNA molecular phylogenetic approach. Methanogenic enrichment cultures were developed in a medium that simulated conditions of soda lake with three different substrates viz., H2:CO2, sodium acetate, and trimethylamine (TMA), at alkaline pH. Archaeal 16S rRNA clone libraries were generated from enrichment cultures and 13 RFLP groups were obtained. Representative sequence analysis of each RFLP group indicated that the majority of the 16S rRNA gene sequences were phylogenetically affiliated with uncultured Archaea. Some of the groups may belong to new archaeal genera or families. Three RFLP groups were related to Methanoculleus sp, while two related to Methanocalculus sp. 16S rRNA gene sequences found in Lonar Lake were different from sequences reported from other soda lakes and more similar to those of oil reservoirs, palm oil waste treatment digesters, and paddy fields. In culture-based studies, three isolates were obtained. Two of these were related to Methanoculleus sp. IIE1 and one to Methanocalculus sp. 01F97C. These results clearly show that the Lonar Lake ecosystem harbors unexplored methanogens.

Aijaz Ahmad Wani

Papers

Bacterial aerobic synthesis of nanocrystalline magnetite.

Molecular analyses of microbial diversity associated with the Lonar soda lake in India: an impact crater in a basalt area.

Phylogenetic Analysis of Methanogenic Enrichment Cultures Obtained from Lonar Lake in India: Isolation of Methanocalculus sp. and Methanoculleus sp.