Silver nanostructures on porous silicon for multiplexed Surface Enhanced Raman Scattering biosensing platforms

Surface Enhanced Raman Scattering (SERS) technique merges an excellent sensitivity and a highly specific label free detection which can be exploited in miniaturized devices with a multiplexed approach. The development of plasmonic nanostructures, aimed to SERS analysis, satisfies therefore the need for point-of-care multianalyte sensing and biosensing platforms, both in the framework of diagnostics and therapy monitoring. In this thesis, SERS active metal-dielectric nanostructures based on silver-coated porous silicon (Ag-pSi) are carefully optimized for biodetection purposes. The thesis is organized in two parts. Basic concepts, necessary to the understanding of the experimental work are provided in the "Background" section, dealing with fundamentals of SERS spectroscopy (Chapter 1), SERS substrates fabrication aimed to biosensing applications (Chapter 2) and the main techniques devoted to the substrates characterization (Chapter 3). On the other side, the "Experimental" part includes the applied materials and methods (Chapter 4) and the presentation and discussion of the experimental results. (Chapters 5-8). In detail, a reliable SERS sensing requires a deep characterization of the optical and SERS response of the substrate providing the Raman enhancement. Theoretical and experimental techniques (FEM simulations and multi-wavelength Raman mapping) are systematically applied to get new insight into the fundamental and applicative SERS properties of Ag-pSi (Chapter 5). Two different approaches for the fabrication of Ag-pSi multianalyte platforms are then presented and discussed. Chapter 6 deals with the in situ synthesis of silver nanoparticles (NPs) patterns synthesized by ink-jet printing. The correlation between the growth parameters, morphology and SERS response is studied in order to optimize the SERS signal efficiency and uniformity of the Ag-pSi printed nanostructures. On the other hand, Chapter 7 concerns with the fabrication of multichamber Ag-pSi-PDMS microfluidic chips, which can be applied as portable SERS multiplexing devices. An all-microfluidic in-flow synthesis of silver NPs is performed, integrating the preparation of the SERS active substrate and the detection step on the same chip. Finally, a biofunctionalization protocol developed for the detection of miRNA222 (a recognized tumor marker) is optimized for the application to the Ag-pSi SERS substrates, assessing their compatibility to bioassays and suggesting the Ag-pSi nanostructures integrated in elastomeric chips as advantageous platforms for miRNA profiling, as well as for several other bioanalytical applications (Chapter 8