Synthesis, multiscale-multiphase characterization and applications of thiophene-based biohybrids

Biohybrid derivatives of π-conjugated materials are emerging as powerful tools to study biological events through the (opto)electronic variations of the π-conjugated moieties, as well as to direct and govern the self-assembly properties of the organic materials through the organization principles of the bio component. So far, very few examples of thiophene-based biohybrids have been reported. The aim of this Ph. D thesis has been the development of oligothiophene-oligonucleotide hybrid derivatives as tools, on one side, to detect DNA hybridisation events and, on the other, as model compounds to investigate thiophene-nucleobase interactions in the solid state. To obtain oligothiophene bioconjugates with the required high level of purity, we first developed new synthetic ecofriendly protocols for the synthesis of thiophene oligomers. Our innovative heterogeneous Suzuki coupling methodology, carried out in EtOH/water or isopropanol under microwave irradiation, allowed us to obtain alkyl substituted oligothiophenes and thiophene based co-oligomers in high yields and very short reaction times, free from residual metals and with improved film forming properties. These methodologies were subsequently applied in the synthesis of oligothiophene-oligonucleotide conjugates. Oligothiophene-5-labeled deoxyuridines were synthesized and incorporated into 19-meric oligonucletide sequences. We showed that the oligothiophene-labeled oligonucletide sequences obtained can be used as probes to detect a single nucleotide polymorphism (SNP) in complementary DNA target sequences. In fact, all the probes showed marked variations in emission intensity upon hybridization with a complementary target sequence. The observed variations in emitted light were comparable or even superior to those reported in similar studies, showing that the biohybrids can potentially be useful to develop biosensors for the detection of DNA mismatches. Finally, water-soluble, photoluminescent and electroactive dinucleotide-hybrid derivatives of quaterthiophene and quinquethiophene were synthesized. By means of a combination of spectroscopy and microscopy techniques, electrical characterizations, microfluidic measurements and theoretical calculations, we were able to demonstrate that the self-assembly modalities of the biohybrids in thin films are driven by the interplay of intra and intermolecular interactions in which the π-stacking between the oligothiophene and nucleotide bases plays a major role.

Electrochemistry of carbon based engineered structures

The main aims of my PhD research work have been the investigation of the redox, photophysical and electronic properties of carbon nanotubes (CNT) and their possible uses as functional substrates for the (electro)catalytic production of oxygen and as molecular connectors for Quantum-dot Molecular Automata. While for CNT many and diverse applications in electronics, in sensors and biosensors field, as a structural reinforcing in composite materials have long been proposed, the study of their properties as individual species has been for long a challenging task. CNT are in fact virtually insoluble in any solvent and, for years, most of the studies has been carried out on bulk samples (bundles). In Chapter 2 an appropriate description of carbon nanotubes is reported, about their production methods and the functionalization strategies for their solubilization. In Chapter 3 an extensive voltammetric and vis-NIR spectroelectrochemical investigation of true solutions of unfunctionalized individual single wall CNT (SWNT) is reported that permitted to determine for the first time the standard electrochemical potentials of reduction and oxidation as a function of the tube diameter of a large number of semiconducting SWNTs. We also established the Fermi energy and the exciton binding energy for individual tubes in solution and, from the linear correlation found between the potentials and the optical transition energies, one to calculate the redox potentials of SWNTs that are insufficiently abundant or absent in the samples. In Chapter 4 we report on very efficient and stable nano-structured, oxygen-evolving anodes (OEA) that were obtained by the assembly of an oxygen evolving polyoxometalate cluster, (a totally inorganic ruthenium catalyst) with a conducting bed of multiwalled carbon nanotubes (MWCNT). Here, MWCNT were effectively used as carrier of the polyoxometallate for the electrocatalytic production of oxygen and turned out to greatly increase both the efficiency and stability of the device avoiding the release of the catalysts. Our bioinspired electrode addresses the major challenge of artificial photosynthesis, i.e. efficient water oxidation, taking us closer to when we might power the planet with carbon-free fuels. In Chapter 5 a study on surface-active chiral bis-ferrocenes conveniently designed in order to act as prototypical units for molecular computing devices is reported. Preliminary electrochemical studies in liquid environment demonstrated the capability of such molecules to enter three indistinguishable oxidation states. Side chains introduction allowed to organize them in the form of self-assembled monolayers (SAM) onto a surface and to study the molecular and redox properties on solid substrates. Electrochemical studies on SAMs of these molecules confirmed their attitude to undergo fast (Nernstian) electron transfer processes generating, in the positive potential region, either the full oxidized Fc+-Fc+ or the partly oxidized Fc+-Fc species. Finally, in Chapter 6 we report on a preliminary electrochemical study of graphene solutions prepared according to an original procedure recently described in the literature. Graphene is the newly-born of carbon nanomaterials and is certainly bound to be among the most promising materials for the next nanoelectronic generation.

Thiophene- Based Materials for Photovoltaic Applications

Thiophene oligomers (OTs) and polymers (PTs) are currently attracting remarkable attention as organic materials showing semiconducting, fluorescent, nonlinear optical and liquid crystalline properties. All these properties can be fine-tuned through minor structural modifications. As a consequence, thiophene oligomers and polymers are among the most investigated compounds for applications in organic electronics, optoelectronics and thin film devices such as field effect transistors (FETs), light emitting diodes (LEDs) and photovoltaic devices (PVDs). Our research aims to explore the self-assembly features and the optical, electrical and photovoltaic properties of a class of thiophene based materials so far scarcely investigated, namely that of oligo- and polythiophenes head-to-head substituted with alkyl or S-alkyl chains. In particular, we synthesized these compounds in short reaction times, high yields, high purity and environmentally friendly procedures taking advantage of ultrasound (US) and microwave (MW) enabling technologies in Suzuki-Miyaura cross-couplings.

Hierarchically organized chitin-based matrices

Chitin is the second most abundant biopolymer on Earth and the most diffused across the known species, being present in more than 70 % of them. It is present in a huge variety of different structures and morphologies being a massive pool of information for new material science approach. This thesis aims to study chitin at different level of organization using diverse approaches. Three main topics are discussed in this manuscript. The first is the use of a bottom-up approach to study chitin nanofibrils self-assembly in water triggering the assembly by pH increment. Successively, the assembly was studied in presence of another pH responsive biomacromolecule, the collagen, to get new composite materials and study how the assembly and the chitin/collagen ratio influence fibroblast’s viability. The second topic focuses on biogenic organized chitin-based matrices, in both Ariolimax californicus and Loligo vulgaris. This study aims to understand the features that give raise to the properties of those matrices. Finally, in the last section a top-up approach was used to exploit natural hierarchically organized chitinous matrices to obtain organized functional materials introducing a catechol on the free amino group of deacetylated chitin (DA 77 %). In conclusion, this study of chitin at different level of organization emphasized different novelties depending on the organization level studied. Moreover, this thesis gives many possibilities for future bioinspired routes to get highly organized materials, or for highly organized functional materials based on natural chitin-based matrices.

Chemiluminescence DNA-based Nanotechnologies for Bioanalytical Applications

DNA as powerful building molecule, is widely used for the assembly of molecular structures and dynamic molecular devices with different potential applications, ranging from synthetic biology to diagnostics. The feature of sequence programmability, which makes it possible to predict how single stranded DNA molecules fold and interact with one another, allowed the development of spatiotemporally controlled nanostructures and the engineering of supramolecular devices. The first part of this thesis addresses the development of an integrated chemiluminescence (CL)-based lab-on-chip sensor for detection of Adenosine-5-triphosphate (ATP) life biomarker in extra-terrestrial environments.Subsequently, we investigated whether it is possible to study the interaction and the recognition between biomolecules and their targets, mimicking the intracellular environment in terms of crowding, confinement and compartmentalization. To this purpose, we developed a split G-quadruplex DNAzyme platform for the chemiluminescent and quantitative detection of antibodies based on antibody-induced co-localization proximity mechanism in which a split G-quadruplex DNAzyme is led to reassemble into the functional native G-quadruplex conformation as the effect of a guided spatial nanoconfinement.The following part of this thesis aims at developing chemiluminescent nanoparticles for bioimaging and photodynamic therapy applications.In chapter5 a realistic and accurate evaluation of the potentiality of electrochemistry and chemiluminescence (CL) for biosensors development (i.e., is it better to “measure an electron or a photon”?), has been achieved.In chapter 6 the emission anisotropy phenomenon for an emitting dipole bound to the interface between two media with different refractive index has been investigated for chemiluminescence detection.

Development of a Computer-Based methodology for tolerance selection and optimization applied to the automotive sector

The design optimization of industrial products has always been an essential activity to improve product quality while reducing time-to-market and production costs. Although cost management is very complex and comprises all phases of the product life cycle, the control of geometrical and dimensional variations, known as Dimensional Management (DM), allows compliance with product and process requirements. Hence, the tolerance-cost optimization becomes the main practice to provide an effective application of Design for Tolerancing (DfT) and Design to Cost (DtC) approaches by enabling a connection between product tolerances and associated manufacturing costs. However, despite the growing interest in this topic, a profitable application in the industry of these techniques is hampered by their complexity: the definition of a systematic framework is the key element to improving design optimization, enhancing the concurrent use of Computer-Aided tools and Model-Based Definition (MBD) practices. The present doctorate research aims to define and develop an integrated methodology for product/process design optimization, to better exploit the new capabilities of advanced simulations and tools. By implementing predictive models and multi-disciplinary optimization, a Computer-Aided Integrated framework for tolerance-cost optimization has been proposed to allow the integration of DfT and DtC approaches and their direct application for the design of automotive components. Several case studies have been considered, with the final application of the integrated framework on a high-performance V12 engine assembly, to achieve both functional targets and cost reduction. From a scientific point of view, the proposed methodology provides an improvement for the tolerance-cost optimization of industrial components. The integration of theoretical approaches and Computer-Aided tools allows to analyse the influence of tolerances on both product performance and manufacturing costs. The case studies proved the suitability of the methodology for its application in the industrial field, providing the identification of further areas for improvement and refinement.