Protein can act as unique template to assemble gold nanoparticles in a linear fashion

Nanoparticles of metals possess unique chemical, electronic, optical and magnetic properties that differ from their bulk counterpart because of the quantum size effects ^[14]. The spatial orientation and arrangement of nanoparticles is important in the realization of technologically useful nanoparticle-based materials ^[5-7]. Nevertheless, the assembly of nanoparticles into defined arrays remains a challenge. There are numerous reports of assembly of gold nanoparticles in a defined manner. In most of them, linker molecules were generally added to a preformed gold nanoparticle solution for assembly. Here a facile process for the assembly gold nanoparticles in a linear fashion has been described using protein as templates. The presence of proteins during the reduction of gold salts by sodium borohydride directs the assembly of gold nanoparticles in a linear fashion when cooled to -80° C followed by thawing at room temperature. Similar results were obtained by cooling at -20°C, whereas no assembly was observed when cooled at 0 ⁰C. Assembly was also not observed when proteins were added to gold nanoparticle solution. Therefore, interaction of gold salts with the protein before the reduction is essential for such an assembly process. The assembled products thus obtained were characterized using transmission electron microscopy (TEM), UV-visible spectroscopy (UV-Vis) and thermogravimetric analysis (TGA).