Engineered LSPR nanosensors based on Metamaterials for Environmental analysis

The progress of the nanotechnology in the last years has made possible to realize tailorable artificial structures for the control of the light in many applications in the photonic field. An example of artificial electromagnetic (EM) materials are the metamaterials (MTMs) as photonic crystals (PCs) and the photonic quasi crystals (PQCs), which are very attractive given that they allow new possibilities to control the EM field in innovative ways. With the use of these classes of materials, it is possible to realize novel optical sensing devices based on the extraordinary plasmonic properties of noble metal nanoparticles characterized by selective EM responses, which undergo significant frequency shifts, in presence of a specific target molecule. Various plasmonic sensors based on nanotechnology have been recently developed for the sensing of low concentrations of molecules of biological or environmental interest. Among them Localized Surface Plasmon Resonance (LSPR) based nanosensors are considered one of the most powerful tools in the biotechnology and sensor fields. They operate trasducing small changes in refractive index near the metallic surface into a measurable wavelength shift response and they have the following notable advantages: high sensitivity, good reproducibility, label-free detection, low cost and easy instrumental setup. In the present work we engineered reproducible LSPR nanosensors based on gold PCs and PQCs patterns realized with different geometries. We use the Electron Beam Lithography (EBL) for the fabrication of these nanosensors. The EBL system permit to control with high precision the size, the shape, but also the inter-particle distance and consequently to tune the plasmonic resonance of the nano-arrays in the visible and near infrared range. The sensitivity of the nanosensors has been evaluated and a value higher than 240 nm/RIU has been obtained for both periodic and a-periodic patterns. The performance of the LSPR nanosensors for enviromental analisys has been tested using a pesticide (Thiram, C6H12N2S4) at different concentrations. A limit of detection of the order of nM has been obtained using a LSPR nanosensor based on a Thue-Morse pattern. These first results indicated that the LSPR nanosensors developed here are expected to demonstrate a wide range of applications for the detection of analites of environmental and biological interest.