Photonics

Among the activities dealing with micro and nano-photonics, our past efforts were focused on the synthesis and characterization (far and near-field based) of Photonic Crystals (PhC). They consist of optical materials with periodic changes in the dielectric constant at a periodicity on a wavelength scale. The periodical modulation can be induced along one, two or three direction of space. This influences the propagation of light in a way which is analogous to the effect that crystalline potentials have on electrons. The interest in such structures has been exploited in the synthesis of periodic multilayers (1D-PhC), arrays of holes within dielectric slabs (2D-PhC) and artificial direct and inverse opals (3D-PhC).

In the recent past, the application of optical nanostructures for sensing has become an active area of our research. The near-field interactions of sensed analytes with optical modes sustained by photonic crystals have resulted in a general increase of the sensing/biosensing performances, both in label-free and labelled configurations. As a particular case, 1D-PhC represents an interesting opportunity for enhancing the light-matter interaction mediated by Bloch Surface Waves (BSW). The use of such electromagnetic surface modes as optical transducers presents some advantages with respect to standard optical detection methods, such as spectral and polarization tunability and low losses.

 

 

 

Besides Photonic Crystals optimized for BSW coupling, metal-dielectric nanostructures characterized by tunable plasmonic resonances, have been developed for Surface Enhanced Raman Scattering (SERS) applications. SERS is a sensitive technique allowing the analysis of vibrational spectra from individual molecules. Among single-molecule spectroscopies, it provides much more detailed information as compared to the broad fluorescence spectra.

We obtained efficient SERS substrates based on Ag/Au nanoparticles embedded in Silicon and polymeric matrices. They are characterized by plasmonic resonances in the visible-near-infrared energy range. For such structures, which can be synthesized on large area, we found noticeable Raman enhancements; single molecule detection has been demonstrated in resonant SERS regime and promising applications have been validated for the analysis of biological assays.

 

 

Contact information

Fabrizio Giorgis
Tel. +39 011 090 7354
fabrizio.giorgis@polito.it

Emiliano Descrovi
Tel. +39 011 090 7354
emiliano.descrovi@polito.it