General Overview of our Research




Nanoparticle synthesis: size and shape control


Morphology control in the nanoscale is a hot topic because of the spectacular effects that small changes in the morphology of nanoparticles have on physical (optical, magnetic, electronic...) properties of the material. Colloidal synthesis has proven extremely useful to prepare a wide variety of nanoparticles with tight control of size and shape. Still, much of the knowledge in this area is empirical and no general rules can be provided for a rational nanomaterial design. We are particularly interested in understanding the mechanisms involved in nanoparticle growth, which determine the final size and shape. Though eminently fundamental, this research is required for the design of nanoparticle materials with tailored properties that can be used for practical applications.
Examples of nanoparticles with various morphologies are shown here.

            



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.

For more information, see a general review.

Examples of EELS plasmon maps for Au nanoparticles with different morphologies are shown here.

      

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Nanoparticle assemblies


The assembly of metal nanoparticles into ordered supercrystals can be exploited to achieve interesting collective plasmonic properties. This is particularly interesting for anisotropic nanoparticles, such as nanorods. Oriented assemblies can be obtained by slow solvent evaporation within micron sized cavities, so that the obtained supercrystals retain the shape of the templating cavities.

Examples of Au nanorod supercrystals at different magnifications are shown here.

      

Nanoparticle assemblies can also be obtained in the form of well-defined clusters, which can even be maintained in colloidal dispersion. Such assemblies have been obtained by exploiting hydrophobic interactions and encapsulation with block copolymers. Such clusters can be made of identical or disimilar nanocrystals, even including multifunctionality.

Examples of nanoparticle clusters are shown here.

         



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.

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Integration of nanoparticles into complex sensors for diagnosis and biodetection

Besides direct approaches in the evaluation of components in a given sample, other powerful approaches include indirect detection by taking advantage of the spectroscopic properties of certain molecular systems. The fabrication of hybrid systems based on nanoparticles is taking prominence as a method for the fabrication of complex sensor elements based on recognition events (key-and-lock sensors) or indirect interactions (cross-reactive arrays). In this research line, we investigate new sensing technologies by using SPR and SES with applications in high-throughput screening and real time analysis.

An example of an ambitious project is the ERC Advanced Grant PLASMAQUO, which aims at the development of novel nanostructured materials based on crystalline assemblies of anisotropic plasmonic nanoparticles, to be used for the surface enhanced Raman scattering (SERS) detection of quorum sensing (QS) signalign molecules, and to the demonstration of applications of such materials to monitor population kinetics in bacterial colonies and the determination of the interaction mechanisms between mixed colonies and their manipulation through external parameters.