Label-free photonic crystal technology for immunosensing applications

The continue request in medical field of methods for the diagnosing and the monitoring of diffuse pathologies like cancer, Alzheimer and muscular dystrophy, has pushed the scientific research to focus its interest in he design of biosensors for fast and in-situ assays. Although several typology of biosensors has been proposed, label-free immunosensors are good candidates in the biomarkers detection thanks to a high bio-selective recognition and a simple read-out. This thesis presents the research activity about the design, fabrication and testing of an immunosensor based on a Si3N4 2-D photonic crystal (PhC) in membrane configuration and further optimizations of the fabrication process of PhC membranes for biosensing applications. The structure has been optimized by means of the finite difference time domain method (FDTD) in order to achieve peaks of reflectivity in the visible-near infrared spectrum. Subsequently, a nano-fabrication protocol exploiting e-beam lithography and dry/wet etching has been optimized, obtaining high resolution structures. Finally, the immunosensor has been functionalized with a layer of antibodies for the detection of the IL-6 protein and experimental tests has been performed, achieving a sensitivity of 1.5 pg/ml. A further step has been the optimization of the fabrication processes of PhC membranes for biosensing applications and their transferring from rigid substrate to flexible polymeric layer in order to achieve high integrable and biocompatible devices.