Colloidal dendritic nanostructures of gold and silver for SERS analysis of water pollutants

Abstract

Surface-Enhanced Raman Scattering (SERS) using colloidal metal (Ag, Au) nanoparticles has been regarded as a powerful method for detecting organic pollutants at vestigial levels. Although less investi- gated, the controlled synthesis of binary nanostructures comprising two metals provides an alternative route to SERS platforms with tuned surface plasmon resonances. Here, we demonstrate that the use of dendrimers allows the formation of distinct combinations of Ag:Au nanostructures that are composed of smaller metal nanocrystals. Our research highlights the role of the dendrimer macromolecules as a multipurpose ligand in the generation of such hybrid nanostructure, including as a reducing agent, an effective long-term colloidal stabilizer and as a molecular glue for interconnecting the primary metal nanocrystals. Noteworthy, the dendrimer-based Ag:Au hybrid nanostructures are more SERS sensitive as compared to the corresponding colloidal blends or to the single-phase metals, as revealed by using molecular pesticides as analytes in spiked water samples. We suggest that the high SERS sensitivity of the hybrid nanostructures is due to interparticle plasmonic coupling occurring between the primary metal nanoparticle aggregates, whose arrangement is templated by the presence of the dendrimer macromolecules.