The effect of arginine on gold nanoparticles in colloidal solutions and in thin films.

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.