Methanobactin-Induced Synthesis Of Gold Nanoparticles

Gold nanoparticles is a common metal nano-material, as opposed to macro-gold, gold nanoparticles have good catalytic properties, sorption properties, and chemical stability. These make it wide range of biomarker, biological chip, micro sensors and chemical catalysis applications. Compared with the traditional physical and chemical synthesis method, biosynthesis method is clean, non-toxic, non-pollution and can be reacted under a mild or controllable conditions. It has a high production,low-price. Thus biosynthesis method has become a focus at gold nanoparticle preparation research. Methanobactin (mb) is a small, copper binding peptide produced by methanotrophic bacteria. It can also be combined with the Ag (Ⅰ), Au (Ⅲ) or other metals, then Au (Ⅲ) is reduced to Au (0). Mb not only can protect gold nanoparticles but also has the reducase activity. It can catalyze the transfer of electron from electron donor to the metal ion and can be used to prepare stabilized gold nanoparticles.The purpose of this paper was focus on the effect on cultivating methanotrophs and producing mb by different supplying ways of carbon sources; Gold nanoparticles were synthesized by methanobactin-induced biosynthesis under the addition of hydroquinone as electron donor; The influence of synthesis conditions and the reaction mechanism were explored.Paraffin was added as the methane vector to improve cell growth. When the concentration of paraffin was2.5%(Ⅴ/Ⅴ), Methane-grown cells has the highest mb production. It can achieve0.51nmol/mL which is slightly higher than that of Methane-grown cells (0.45nmol/mL). The mb production ability of methanol-grown cells were obviously higher than that of methane-grown cells at the optimum methanol addition (0.05%), which is0.67nmol/mL. By optimum addition of methane and methanol as carbon sources, the highest mb production (0.79nmol/mL) can be obtained with optimum methanol addition (0.05%) in cultivation of Methanotrophs. It has the highest mb production among other carbon sources.The synthesis of gold nanoparticles by methanobactin-induced biosynthesis was conducted under hydroquinone as electron donor.The optimum synthetic conditions were as below:Both1mL1mM mb and1mL1mM HAuCl4were added in5ml solution (mb:HAuCl4=1:1),100μL5×10-4M of hydroquinone solution, reaction time80min, reaction temperature35℃; By adjusting the addition of1mM mb and5×10-4M hydroquinone, mb can induce the synthesis of different particle size of gold nanoparticles under different reaction conditions such as1mL and100μL、1.5mL and150μL、2mL and50μL、2.5mL and250μL、0.5mL and200μL which the average particle size is9nm,15nm,33nm,66nm,100nm. With UV-Vis absorption spectroscopy and transmission electron microscope scanning, it can be found that gold nanoparticles size is gradually increasing. As transmission electron microscope scanning shows, colloidal gold nanoparticles was spherical. It can as a method of synthesis of nano-gold particles with specified diameter.The possible reaction mechanism of mb-induced gold nanoparticles synthesis were researched, mb has a pyramid structure with a bottom of sulfonyl imidazole groups. The groups can be combined with Cu (Ⅱ) or Au (Ⅲ). Mb has the capacity of catalyzing and reducing Au (Ⅲ) and can synthesize gold nanoparticles. While the ability is weak, it can not be sustained reducing Au (Ⅲ). Mb has reducase activity that can catalyze the transfer of electron from electron donor to the metal ion. Thus we can use methanobactin-induced biosynthesis to synthesize large amount gold nanoparticles under the addition of hydroquinone as electron donor. Gold nanoparticles were synthesized by mb catalyzing and reducing Au (Ⅲ). H ydroquinone can reduce Au (Ⅲ) only in the condition of mb catalysis. Mb can adsorb gold nanoparticles with S-Au bonds to protect them and catalyze this reaction process. Mb can be adsorbed on the surface of gold nanoparticles by S-Au bonds. Sulfonyl imidazole groups at the bottom of mb can be combined with Cu (Ⅱ) or Au (Ⅲ). This lead to mb-Cu synthetizing little amount gold nanoparticles than that of mb. When Cu (Ⅱ) was added in the gold nanoparticles solution, the gold nanoparticles gather together to form large particle size gold nanoparticles. The reason is that mb adsorbed on the surface of gold nanoparticles by S-Au bonds has been combined by the Cu-mb covalent bond.