Capasso, Rossella (2014) 2D Highly sensitive plasmonic "label-free" nanobiosensors based on Photonic Crystals and Photonic Quasi-Crystals. [Tesi di dottorato]

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In the last decade, artificial Electro Magnetic (EM) materials, including photonic crystals (PCs) and photonic quasi-crystals (PQCs), have remarkably attracted the scientific community, due to the new possibilities enabled - still largely unexplored - to control the EM field in an unprecedented way. The potentials exhibited by such materials in several application scenarios are also of interest in the field of biological sensing. The principal object of this PhD research activity is the design, fabrication and characterization of plasmonic nanostructures to be used as plasmonically-active Surface Enhanced Raman Scattering (SERS) substrates for biosensing.In order to fabricate SERS-active substrates suitable for sensing applications, a well-tested nanofabrication process by electron-beam lithography (EBL) technique, for the realization of easily manufacturable and reproducible devices, has been developed passing through the necessary design steps, and arriving at the fabrication, optical characterizations and experimental SERS characterizations first with a commercial molecular probe (p-mercaptoaniline - pMA) and then using a culture of Human prostate deseased cells as real analyte. Herein, we report our successful attempt to utilize both bottom-up approach and a top-down technique to realize efficient SERS substrates. An effective and facile method for the fabrication of a SERS-active film with Silver nanowires (NWs) is proposed by drop casting of Silver NWs on glass with ethanol as the inducer. Alternatively, Au PCs and PQCs are proposed for the engineering of reproducible SERS substrates. Using a molecular monolayer of pMA as a Raman reporter, we show that high values of SERS enhancement factors can be achieved in PQCs structures and in Silver NWs substrates. To demonstrate the feasibility of the fabricated nanostructures as efficient SERS substrates for biological applications, we devised a method to deposit single cells (human prostatic) on the photonic surfaces. Preliminary results on SERS sampling of single prostatic human cells indicated that the proposed engineered metamaterials may be used as an ultrasensitive Raman probe to monitor subtle molecular changes in the cell and open up interesting new opportunities in biosensing. These type of sensors would likelihood represent a promising step toward future reproducible single-molecule detection using engineered plasmonic substrates.

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