Assembly of gold nanoparticles in a rod-like fashion using proteins as templates

An area of considerable current interest is the development of a practical approach for assembling inorganic nanoparticles into well-defined arrays because such a technique would offer immense opportunities leading to applications in microimaging, optoelectronics, therapeutics, etc. This paper illustrates a new, simple one-step process in which proteins act as templates to assemble gold nanoparticles in a shape-selective fashion. We show, for the first time, that antibodies to vascular endothelial growth factor 165 isoform, 2C3, and epidermal growth factor receptor can act as templates when present in solution during the synthesis of gold nanoparticles. These proteins direct the assembly of the gold nanoparticles into rod-like shapes when cooled to -20°C followed by thawing at room temperature. Immunoglobulin G and bovine serum albumin can also direct the assembly process in a similar fashion; however, small molecules, such as poly(L-lysine) and lysine, cannot. The formation of a self-assembled structure in the form of a continuous rod, or the assembly of discrete nanoparticles in a rod-like fashion, can be tailored by controlling the ratio of the precursor gold salt, HAuCl₄, to the antibody/protein used as the template. The nanoconjugates are characterized using UV-vis spectroscopy, transmission electron microscopy, and infrared spectroscopy. The nano-bioconjugates obtained via this process may find wide application in areas ranging from optoelectronics and biosensors to therapeutics in neoplastic disorders.