Site-selective immobilization of gold nanoparticles on graphene sheets and its electrochemical properties

The site-selective attachment of metal nanoparticles (NPs) on graphene surface is highly desirable for various applications such as electrochemical sensors and catalysts. Here, we present a simple and effective synthetic approach for the site-selective immobilization of gold NPs (AuNPs) on either basal planes or edges of graphene sheets. The basic principle of this approach is to use cyteamine linker with reactive amine and thiol functional groups at each end, where the amine groups at one end covalently bind to functional groups presented on edges and/or basal planes of chemically synthesized graphene sheets, and the thiol groups at the other end assemble onto pre-synthesized AuNPs through thiol-Au interaction. Due to the difference in the spatial distribution of functional groups presented on graphene oxide (GO) and reduced graphene oxide (rGO) sheets, most of AuNPs are homogeneously immobilized on the basal planes of the cysteamine-functionalized graphene oxide (GO-SH) sheets, whereas AuNPs are selectively attached at the edge parts of the cysteamine-functionalized reduced graphene oxide (rGO-SH) sheets. Raman signals of GO-SH/Au hybrid films with the high content of AuNPs in the hybrids are clearly increased owing to the formation of the charge-transfer complex between AuNPs and GO-SH sheets, exhibiting surface-enhanced Raman scattering (SERS) activity.