The interdisciplinary scientific activity at Nanostructure Department is mainly based on the design and fabrication of novel nano-devices and on their use for facing basic and applied problems in modern material science, biology and nanomedicine.
The activity is based on four main themes:
Delivering of Energy at the Nanoscale.
Energy delivery at the nanoscale regards the problems that emerge when a source of energy of macroscopic extension, such as a laser, or in general an electromagnetic field, has to efficiently interact through an energy exchange with the matter and the nanostructures. This problem is the starting point of many others in different fields, such as nanolithography, nanospectroscopy, design of efficient photovoltaic systems, opto energy transfer in biology, novel concepts of nanolithography (also applied to biological materials) etc.
We are optimizing the design and fabrication of nanostructures that generate localized or propagating Surface Plasmon Polaritons (SPP). The nanostructures will be the artificial medium for delivering the energy at nanoscale, according to the specific needs involved in the problem. Plasmonics is the “trait de union” between all activities in the department.
Therefore the development of advanced novel instrumentation for enhanced nanospectroscopy represents an important step and is treated as a problem of energy delivering at Nanoscale. SERS (Surface Enhanced Raman Spectroscopy) based on continuous wave Laser source, or CARS (Coherent Anti Stokes Raman Scattering) or the more advanced RRS (Resonant Raman Scattering) based of ultrafast sources will be mediated by a nanostructure, in order to obtain, chemical resolution and spatial resolution at nanoscale at the same time.
Novel devices for Single Molecule Detection
“The ability to analyze biological systems at the single molecule level opens avenues of investigation that are not possible using techniques that measure aggregate properties of molecular populations. This new vantage point can yield important insights” (Nature Methods, 2008)
The department activity has conducted to important results obtained in the label-free detection of few/single molecules from highly diluted solution. Such kind of research is directly related to early stage pathology studies where the definition and the detection of markers represents a breakthrough in treatment.
Direct characterization for label-free detection of biological molecules such as proteins, nucleic acids or pathogens, is of real importance since it avoids the use of an intermediary molecular species. Such a direct characterization is possible by the use of vibrational spectroscopies. Indeed, vibrational spectroscopies, such as IR absorption and Raman scattering, are powerful tools for label-free characterization of biological species since the vibrational modes are actual fingerprints of both the whole molecule (i.e. chemical bonds, conformation, 3D structure) and its local interaction with other molecules (i.e. binding between two molecules). Unfortunately, IR absorption and Raman scattering cross-sections, when used on a highly diluted number of molecules, are very low and consequently, the spectroscopic signal to noise ratio is poor. Therefore, the device we developed, is designed to obtain a field enhancement that is created in the vicinity of a metallic nanostructure surface and has specific properties: it can be controlled through physical parameters and optical properties of the particles (i.e. localized surface plasmon resonance) and it can reach several orders of magnitude. Exploiting such field enhancement in vibrational spectroscopy has indicated the way towards extreme amplification of the vibrational signal (enhancement factor of 1012 for SERS and 3x105 for SEIRA) and has allowed the observation of a very low amount of molecules (around 100 000 molecules in SEIRA) or even the single-molecule sensitivity in SERS.
Novel methods and devices for Opto genetics studies
In this activity, started during 2011, we are buiding a novel generation of biologically inspired molecular devices (MDs), based on the developments of new photonic tools that will be interfaced with electrophysiology tools. These photonic tools will use Plasmon Polariton technology, enabling focused light spots with a diameter around 10 nm. The main difficulty we are facing is the design and fabrication of a photonic-plasmonic device with very low background, where the excitation of the photosensitive molecule is highly localized in the space and few/single molecules are directly illuminated (negligible background) through the nanostructure. Another important aspect of the technology under development is the light intensity delivered to the molecule; we will also develop new light sensitive molecules that will be selectively activated by our new photonic tools. These new technological innovations will provide a way to control the activation of single light sensitive molecules and will allow the investigation of molecular computation in a biological environment and with an unprecedented resolution.
Metal-Semiconductor Hybrid Nanosystems
Metal nanostructures are very good conductors and can strongly interact with light in the visible and infrared spectral regions due to the presence of free electrons that can perform plasmon oscillations. The band gap in semiconductor nanocrystals, and consequently their optical and electrical properties, depend strongly on their size, shape and composition.
The aim of the research activity is to combine the favorable properties of both worlds in order to investigate complex optoelectronic systems and to pave the way for novel architectures for components in photodetectors, optical communication, photovoltaics, and nanoscale electronics.