Facile synthesis of silver nanoparticles using unmodified cyclodextrin and their surface-enhanced Raman scattering activity

A simple and one-pot approach to synthesise silver nanostructures of different sizes and shapes in aqueous medium at room temperature is reported. The reduction of the silver salt and the stabilization of the as-prepared silver nanostructures are achieved using a macrocycle, the unmodified beta-cyclodextrin, under alkaline conditions at room temperature. This green approach, which utilizes water as a benign solvent and the non-toxic and biocompatible beta-cyclodextrin as both the reducing and the protecting agent at room temperature, does not need any additional reducing agents and external energy under ambient experimental conditions. Furthermore, we are able to prepare silver nanostructures of different sizes and shapes by simply altering the reaction conditions such as the concentration or temperature. The results show that spherical, polygonal, rod-, flower-, wire- and ant-like silver nanostructures are achieved by using an alkaline solution of unmodified beta-cyclodextrin under different experimental conditions without adding additional agents. Furthermore, we demonstrate that the as-prepared silver nanostructures can be used as efficient surface-enhanced Raman scattering active substrates, and p-aminothiophenol is used as a Raman probe to evaluate their enhancement ability. It was found that the enhancement ability of the agglomerated silver nanostructures is higher than that of the well-dispersed and smaller sized silver nanoparticles. The reason for this is discussed from the point of electromagnetic and chemical mechanisms in addition to the agglomeration behaviour of silver nanoparticles, which gain a stronger surface-enhanced Raman scattering effect than the isolated silver nanoparticles because of the coupling between the silver nanoparticles.