Surfactant-directed multiple anisotropic gold nanostructures: synthesis and surface-enhanced Raman scattering

A facile and effective method for the synthesis of gold nanostructures using beta-cyclodextrin in aqueous alkaline medium is reported. The results demonstrate that leaf-like, rugged, dendritic, and tadpole-shaped gold nanostructures are obtained with high yield for the first time under the same experimental conditions by using four different surfactants. To study the effect of surfactant on the shape of the nanoparticles, the experiments were also carried out in the absence of surfactant and in the presence of poly(1-vinyl-2-pyrrolidone). The growth process of the dendritic gold nanostructures formed was investigated by withdrawing samples from the heated solution and examining the intermediate products formed by transmission electron microscopic analysis. The formation mechanism of the anisotropic gold nanostructures is discussed, and it is demonstrated that the cooperative effect of cyclodextrin and the surfactant molecules determines the ultimate morphology of the gold nanostructures obtained. In addition, the effect of the as-prepared nanostructures as an active material in surface-enhanced Raman scattering has been investigated by employing 4-aminothiophenol as a probe molecule. Thus, different enhancement signals are obtained for the different nanostructures; the dendritic nanostructures showed the strongest intensity of the SERS signals and smallest for the leaf-like nanostructures.