Biological synthesis of copper/ copper oxide nanoparticles

Biological synthesis of nanomaterials is a unique way of fabricating nanomaterials using a range of organisms as microbial cell factories due to their ability to reduce metal salts. Copper/copper oxide is important nanomaterial that can be synthesized using chemical routes, but involves eco-toxic solvents, harsh reaction conditions, etc. Therefore, there is an increasing demand to develop non-toxic, environmentally-benign ¿green¿ approaches for Cu nanoparticles synthesis with the possibility of stabilizing these nanoparticles in an aqueous environment. Recently, we showed the ability of Morganella sp, a silver resistant bacterium to synthesize anisotropic Ag nanoplates by controlling the bacterial growth kinetics. It is important to note that the proteins involved in silver and copper resistance mechanism are known to have a high degree of similarity. Hence we envisaged that this bacterium would act as a model organism to explore Cu nanoparticles biosynthesis. We herein demonstrate for the first time that exposing Morganella sp. (M. morganii and M. psychrotolerans) to Cu+2 ions results in formation of ultra-small spherical copper/copper-oxide nanoparticles of 7-15 nm diameters. The materials were characterized using a range of techniques such as TEM, HR-TEM, UV-vis spectroscopy, XPS, and cyclic voltammetry. The cyclic voltammogram showed the presence of two copper species suggesting the possibility of having copper particles stabilized by copper-oxide particles in an aqueous environment. This is particularly important considering that there have been very few reports for biological synthesis of Cu/CuO nanoparticles. This work will not only open up new avenues towards developing a biological means to synthesize these materials.