Comparison between plasmonic and high index dielectric nanoparticles for refractometric sensing

Due to their extraordinary plasmonic properties, gold nanoparticles have been widely used for a variety of applications and localized surface plasmon resonance (LSPR) has become a powerful biosensing technique. This technique allows for label-free, rapid and real time detection, which makes it one of the first candidate for medical diagnostics, environmental monitoring, and food safety. Unfortunately, metallic nanoparticles present high dissipative losses and optical heating. To overcome this problem, in the last decade the use of high index dielectric materials, instead that metallic ones, have been proposed. These materials, like Si, do not support plasmons but they support the so-called Mie resonances, or geometrical resonances. Both plasmonic and geometrical resonances depend, among other things, on the refractive index of their surrounding medium, which allow us to perform refractometric sensing. Even if a sensing platform based on high index dielectric materials seems promising, due to the low losses they present, there are still uncertainties on the sensitivity they can reach. In this project we try to perform an unbiased comparison between a plasmonic and a high index dielectric-based sensing platform. In order to do so, we perform a spectroscopic investigation. An optical transmission setup was built, used together with a microfluidic setup, which allow us to change the refractive index of the samples' surrounding medium (bulk refractometric sensing) or near the samples' surface (local refractometric sensing). This setup allows for continuous real-time measurements of extinction spectra. Both the resonance shifts, and the intensity shifts have been tracked, which permits us to define the sensitivity of the sensor. The results presented in this thesis underline the differences found in the performances of these two different sensing platforms and their possible future applications.