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)

SERS-active metal-dielectric nanostructures integrated in microfluidic devices for ultra-sensitive label-free miRNA detection

In this work, silver decorated porous silicon membranes integrated in a polydimethylsiloxane multi-chamber microfluidic chip were functionalized with DNA-probes and used for the detection of miRNA by Surface-enhanced Raman Scattering analysis. An innovative biological protocol has been designed: the probe was divided in two short pieces that interact before and after the miRNA incubation. The optofluidic biosensor was applied for the label-free detection of miRNA sequences at in vivo concentrations

Monitoring Chemical Changes of Coffee Beans During Roasting Using Real-time NIR Spectroscopy and Chemometrics

Variations occurring in coffee beans during roasting are ascribable to several chemical-physical phenomena: to quickly track the whole process and to ensure its reproducibility, a process analytical technology (PAT) approach is needed. In this study, a method combining in-line Fourier transform near-infrared (FT-NIR) spectroscopy and chemometric modelling was investigated to get real-time and practical knowledge about the roasting effects on coffee’s chemical-physical composition. In-line spectra were acquired by inserting a NIR probe into a laboratory coffee roaster, running twenty-four roasting experiments, planned spanning different coffee species (Arabica and Robusta), four roasting temperature settings (TS1–TS4) and times (650–1580 s). Multivariate curve resolution-alternate least squares (MCR-ALS) was used to model the chemical-physical changes occurring during the roasting process, and information about maximum rate, acceleration and deceleration of the process was obtained, also highlighting potential effects due to the different roasting temperatures and coffee varieties. The proposed approach provides the groundwork for direct real-time implementation of rapid, non-invasive automated monitoring of the roasting process at industrial scale

Graphene-metal nanostructures as surface enhanced Raman scattering substrates for biosensing

Multilayered structures composed by Single Layer Graphene (SLG), silver nanoparticles and polydimethylsiloxane membranes were used as SERS substrates for the analysis of porphyrins and hemoproteins (e.g. Myoglobin). The transfer process of SLG from its Cu growth substrate to the Ag-decorated polydimethylsiloxane membrane was optimized. A Limit of Detection (LOD) of 10^-8 M was found for ethanolic solutions of Rhodamine 6G and the efficient detection of porphyrins and Myoglobin, adsorbed on SLG surface, was achieved. This study evidenced the potentialities of plasmonic graphene-based chips for biosensing

Osteoporosis-related variations of trabecular bone properties of proximal human humeral heads at different scale lengths

Abstract Osteoporosis (OP) is a skeletal disorder responsible for the weakening of the bone structure and, consequently, for an increased fracture risk in the elderly population. In the past, bone mineral density (BMD) variation was considered the best OP indicator, but recently the focus has shifted toward the variation of microstructural bone parameters. This work is based on the characterisation of 8-mm cylindrical biopsies harvested from proximal humeral heads belonging to healthy and osteoporotic patients, in order to assess the OP-related variations of bone properties at different scale lengths. In particular, bone biopsies underwent micro-computed tomography analysis to study the most relevant features of bone architecture and extrapolate the tissue mineral density (TMD) value of bone trabeculae. Compression tests and nanoindentations were performed to investigate the macro- and micromechanical properties of bone biopsies, respectively. In addition, XRD analyses were performed to obtain the mean hydroxyapatite (HA) crystallite size, while Raman spectroscopy investigated the collagen secondary structure. Thermogravimetric analysis was performed to evaluate the ratio between organic and inorganic phases. From the obtained results, OP samples showed a more anisotropic and less interconnected structure responsible for reduced compression strength. From this, it can be supposed that OP caused an alteration of bone structure that led to inferior macroscopic mechanical properties. Furthermore, OP samples possessed higher TMD and bigger HA crystals that are correlated to an increase of the hardness value obtained by means of nanoindentation. This less controlled HA crystal growth is probably due to an alteration of the organic matrix structure, as revealed by the increase of the random coil contribution in the Raman spectra of the OP bone. This higher crystal content led to an increase in trabecular density and hardness. In conclusion, the obtained data showed that OP affects bone properties at different scale lengths causing an alteration of its morphological, structural and mechanical features

Bi2O3/Nylon multilayered nanocomposite membrane for the photocatalytic inactivation of waterborne pathogens and degradation of mixed organic pollutants

Worldwide there is an increasing demand for clean water and sanitation systems and any different solutions are under evaluation, including advanced oxidation processes such as photocatalysis. This work describes the scalable synthesis process of an electrospun composite membrane made of Nylon and embedded α/β-Bi2O3 nanoparticles that can be activated by visible light instead of UV light typically used with other nanomaterials (e.g. TiO2). As a proof of concept, the efficacy of the α/β-Bi2O3 electrospun composite membrane in the visible light inactivation of pollutants and pathogens was demonstrated in a Continuous-flow Photocatalytic Membrane Reactor, highlighting the great potential of this advanced photocatalytic process for clean water and sanitation

Edge-Grafted Molecular Junctions between Graphene Nanoplatelets: Applied Chemistry to Enhance Heat Transfer in Nanomaterials

The edge-functionalization of graphene nanoplatelets (GnP) was carried out exploiting diazonium chemistry, aiming at the synthesis of edge decorated nanoparticles to be used as building blocks in the preparation of engineered nanostructured materials for enhanced heat transfer. Indeed, both phenol functionalized and dianiline-bridged GnP (GnP-OH and E-GnP, respectively) were assembled in nanopapers exploiting the formation of non-covalent and covalent molecular junctions, respectively. Molecular dynamics allowed to estimate the thermal conductance for the two different types of molecular junction, suggesting a factor 6 between conductance of covalent vs. non-covalent junctions. Furthermore, the chemical functionalization was observed to drive the self-organization of the nanoflakes into the nanopapers, leading to a 20% enhancement of the thermal conductivity for GnP-OH and E-GnP while the cross plane thermal conductivity was boosted by 150% in the case of E-GnP. The application of chemical functionalization to the engineering of contact resistance in nanoparticles network was therefore validated as a fascinating route for the enhancement of heat exchange efficiency on nanoparticle networks, with great potential impact in low-temperature heat exchange and recovery application