Plasmonics of metal nanoparticles

Nanoparticles of noble metals (Au, Ag, Cu) display very interesting optical properties due to so-called surface plasmon resonances, which involve the collective oscillation of conduction electrons in resonance with the alternating electric field of incident electromagnetic radiation, as sketched below.

The frequency of the surface plasmon mainly depends on the nature (dielectric function) of the metal, but is largely affected by the size and shape of the nanoparticles, or by their dielectric environment, among other parameters. Such resonances result in bright colours, as well as large enhancements of the electric field around the particles.

One of the main interests of our group is the fine tuning of the optical response of metal nanoparticles with tailored composition, size and shape. Characterization of plasmon modes is carried out both for single nanoparticles and their assemblies. Chiral plasmonics is an emerging area where major efforts are being dedicated.

For more information, see a general review.

Evaluation of the optical enhancing properties of nanoparticles and nanoparticle arrays

Surface enhanced spectroscopies (SERS, SEF and SEIRA), with detection limits down to the single molecule regime, are known to be the ultimate analytical tools. This family of techniques is also called plasmon assisted spectroscopies because of the need of metallic nanoparticles to provide the electromagnetic field necessary for optical enhancement. Key aspects of the enhancing activity of nanostructures are related with size, shape, composition and surface chemistry of the nanoparticles. In this research line, we evaluate the suitability of different colloids and assemblies for SERS and direct sensing.