The aggregation of plasmonic nanoparticles (NP) of different metals is a relatively new topic. Plasmonic nanoparticles (often gold or silver NPs) can interact with electromagnetic waves, which lead to oscillating electrons in the material. This effect has possible applications in the fields of catalysis, spectroscopy, and solar energy generation.

Robertino Università degli Studi di Roma “La Sapienza”, Rome, Italy, Andrea Secchi, Università degli Studi di Parma, Italy, and colleagues have synthesized aggregates of gold and silver NPs. The team covered gold nanoparticles (AuNPs) with 1-dodecanethiol and N-alkyl pyridinium units. They then added these AuNPs to silver nanoparticles (AgNPs) functionalized with ω-alkylthiolate calix[4]arenes. The calix[4]arene moieties of the “host” AgNPs recognize the cationic pyridinium units of the “guest” AuNPs, leading to aggregation of the particles in solution (see picture).

The specific recognition was demonstrated in solution in weakly polar solvents by UV/Vis spectroscopy and dynamic light scattering (DLS) measurements. The extent of aggregation, measured through the low-energy shift of the surface plasmon bands (SPBs), was strongly dependent on the loading of the pyridinium moieties present in the organic layer of the AuNPs.

• Calix[4]arene-Functionalised Silver Nanoparticles as Hosts for Pyridinium-Loaded Gold Nanoparticles as Guests,
  Francesco Vita, Alice Boccia, Andrea G. Marrani, Robertino Zanoni, Francesca Rossi, Arturo Arduini, Andrea Secchi,
  Chem. Eur. J. 2015.
  DOI: 10.1002/chem.201501920