Adriano Colombelli

Surface Plasmon Resonance Optical Sensors for Engine Oil Monitoring

Lubricant systems are fundamental in engines (automotive, aviation, rail etc.) and in any industrial system where surfaces of moving mechanical parts are in contact. An improper lubrication due to oil degradation over a long period of time can lead to unwanted component failure and increased maintenance costs. Present study, unlike methods developed until now for detecting oil degradation (loss of mechanical, physical, chemical and optical properties) focuses on the development of a Surface Plasmon Resonance (SPR) transduction methodology able to measure lubricant degradation in real time observing the change in the refractive index. This approach answers to environmental regulation and user requirements on performance, lifetime expectancy and engine efficiency.

Magneto-Optical properties of noble-metal nanostructures: functional nanomaterials for bio sensing

Metallic nanostructures supporting Localized Surface Plasmon Resonances (LSPR) are characterized by their unique ability to control and manipulate light at the nanoscale. Noble metal nanostructures, such as gold nanostructures, are demonstrating to exhibit magneto-optic activity in the presence of modulated magnetic field of low intensity in transversal configuration (T-MOKE). Validation of experimental findings was achieved by numerical simulations based on Finite Element Method (FEM) techniques. The developed numerical models allowed studying the combination of the T-MOKE effect with the localized surface plasmon resonance of metal nanoparticles. Numerical optical and magneto-optical spectra provided a deep insight on the physical aspects behind the magneto-optical activity of metal nanostructures strictly related to direction of oscillations electrical dipoles generated in resonance conditions. Additionally the MO signal was characterized as a transducing signal for refractive index sensing in liquid conditions. The outcome is an increase in the limit of detection of magneto optical transducer with respect to traditional plasmonic sensors. A new strategy for magneto-plasmonic sensing based on the use of glass supported -Au nanostructures based on their MO properties has put forward.

Interaction-tailored organization of large-area colloidal assemblies

Colloidal lithography is an innovative fabrication technique employing spherical, nanoscale crystals as a lithographic mask for the low cost realization of nanoscale patterning. The features of the resulting nanostructures are related to the particle size, deposition conditions and interactions involved. In this work, we studied the absorption of polystyrene spheres onto a substrate and discuss the effect of particle–substrate and particle–particle interactions on their organization. Depending on the nature and the strength of the interactions acting in the colloidal film formation, two different strategies were developed in order to control the number of particles on the surface and the interparticle distance, namely changing the salt concentration and absorption time in the particle solution. These approaches enabled the realization of large area (≈cm2) patterning of nanoscale holes (nanoholes) and nanoscale disks (nanodisks) of different sizes and materials.

Three-dimensional Plasmonic Materials for Chemical Sensor Application

In this work, we perform a numerical and experimental comparison of 2D and 3D systems of plasmonic nanostructures in order to explore several key parameters for sensitivity enhancement of traditional LSPR biosensors. The optical properties and the sensing capabilities of planar and three-dimensional distributions of metal nanostructures have been theoretically and experimentally investigated. We developed a numerical model for calculating the absorption spectra and the sensitivity towards increasing refractive indexes of periodic array of plasmonic nanostructures. Our numerical results have been verified performing a sensitivity comparison of 2D and 3D nanostructured systems composed by the same kind of metal nanoparticles. As proof of concept, our experiment were conducted on a planar distribution of gold nano-spheres and an hybrid 3D plasmonic material composed by a disordered system of silica nanowires decorated with spherical gold nanoparticles.

Propagating and Localised Plasmonic and Magneto-Plasmonic Transductors for Gas and Biosensing Applications

Surface Plasmon Resonance (SPR) is known as a leading technology for label-free biosensing. It is based on the optical detection of refractive index changes occurring at a metal/dielectric interface upon a proper choice of the metal layer, its thickness as well as on the excitation light beam. Biological and chemical analysis are achieved by functionalizing the gold surface with surface bioreceptors and measuring the shift of corresponding optical signals when a biomolecular reaction occurs. In order to increase the sensing performances two strategies have been adopted: a proper combination of noble metal and ferromagnetic materials tailored on the nanoscale is used as novel transducer in SPR-based biosensor coupled with an external magnetic field; and a new 3D transductor consisting of silica nanowires decorated by gold nanoparticles have been realized to increase the performance of sensing devices In both case increasing biosensing performance have been demonstrated.

FEM Modeling of Nanostructures for Sensor Application

A theoretical comparison of the optical and electronic properties of metallic nanostructures characterized by complementary geometries is proposed in this work. Periodic array of nanoparticles on glass substrate and nano-holes on metal substrate have been analysed performing finite element analysis with the RF Module of COMSOL Multiphysics. Single and array of gold nanostructures have been studied, exploring several key parameters responsible for sensitivity enhancement of LSPR sensors. The analysed structures show a minimum in their spectral transmittance, confirming that regular arrays of nano-holes in thin metal films as well as nano-disk arrays may support localized surface plasmon resonance.