Biological Synthesis of Metallic Nanoparticles by Bacteria, Fungi and Plants

Abstract

Over the past few decades interest in metallic nanoparticles and their synthesis has greatly increased. This has resulted in the development of numerous ways of producing metallic nanoparticles using chemical and physical methods. However, drawbacks such as the involvement of toxic chemicals and the high-energy requirements of production make it difficult for them to be widely implemented. An alternative way of synthesising metallic nanoparticles is by using living organisms such as bacteria, fungi and plants. This "green" method of biological nanoparticle production is a promising approach that allows synthesis in aqueous conditions, with low energy requirements and low-costs. This review gives an overview of some of these environmentally friendly methods of biological metallic nanoparticle synthesis. It also highlights the potential importance of these methods in assessing nanoparticle risk to both health and the environment.techniques, which are generally low-cost and high-volume. However, the need for toxic solvents and the contamination from chemicals used in nanoparticle production limit their potential use in biomedical applications [15]. Therefore a "green", non-toxic way of synthesising metallic nanoparticles is needed in order to allow them to be used in a wider range of industries. This could potentially be achieved by using biological methods.Many bacteria, fungi and plants have shown the ability to synthesise metallic nanoparticles and all have their own advantages and disadvantages (Table 1) [16][17][18]. Intracellular or extracellular synthesis, growth temperature, synthesis time, ease of extraction and percentage synthesised versus percentage removed from sample ratio, all play an important role in biological nanoparticle production. Finding the right biological method can depend upon a number of variables. Most importantly, the type of metal nanoparticle under investigation is of vital consideration, as in general organisms have developed resistance against a small number of metals, potentially limiting the choice of organism. However synthetic biology; a nascent field of science, is starting to address these issues in order to create more generalised chassis, able to synthesise more than one type of metallic nanoparticle using the same organism [19]."Natural" biogenic metallic nanoparticle synthesis can be split into two categories. The first is bioreduction, in which metal ions are chemically reduced into more stable forms biologically. Many organisms have the ability to utilise dissimilatory metal reduction, in which the reduction of a metal ion is coupled with the oxidation of an enzyme [20]. This results in stable and inert metallic nanoparticles that can then be safely removed from a contaminated sample. The second category is biosorption. This involves the binding of metal ions from Journal of Nanomedicine & Nanotechnology J o u rna l of N a n o m ed icine & N a n o te chnolo g y

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