Dottorato in SCIENZE CHIMICHE

Titolo della tesi: Nanostructured materials for sensing and drug delivery applications

Self-assembled nanomaterials are finding a wide variety of applications in the area of nanotechnology, especially in the fields of imaging, sensing and biomedical sciences, thanks to their enhanced surface-to-volume ratio and quantum confinement effect. Self-assembly, that is the process of association of individual units of a material into organised structures through non-covalent interactions, is simple, spontaneous, scalable, versatile and imparts unique properties to both inorganic and organic structures. The production and characterisation of nanomaterials remain challenging, but researchers are continuously developing new synthetic and analytical techniques to overcome these difficulties. In the field of sensors, the necessity for miniaturisation is one of the primary forces behind the development of new sensing tools. As electronic devices and other products become smaller and smaller, there is a need for materials that can be made into tiny components with high performance. Nanomaterials are being used to develop new types of biosensors that can detect environmental pollutants or signals related to different health problems at an early stage. In this regard, self-assembled nanostructures, such as self-assembled monolayers (SAMs) and nanoclusters, offer several advantages including their ability to form ordered structures with high surface area and controlled composition. That makes them ideal for immobilising bioreceptors, such as antibodies, which may allow the detection of specific target molecules with high sensitivity and specificity. In the biomedical field, the application of nanomaterials may play a key role in diagnosis, biosensing and bioimaging devices as well as in the development of drug delivery systems. In bioimaging and tracking, self-assembled nanomaterials can provide a versatile platform for designing multifunctional contrast agents and facilitating simultaneous visualisation of multiple biological processes. Their tunable properties enable tailored surface modifications, ensuring efficient cellular uptake and improved in vivo stability, enhancing the precision and sensitivity of imaging and tracking applications. In drug delivery applications, self-assembled nanoparticles have the potential to improve drugs bioavailability by enhancing their solubility, stability, and targeting ability. Nanoparticles can also protect drug from degradation and reduce drug cytotoxicity. In addition, drug biodistribution and release profile can be finely tuned by varying nanoparticles surface properties, size, and shape. The aim of this dissertation was to explore the possible applications of self-assembled nanostructures in the fields of sensing and drug delivery. Organic and inorganic nanomaterials obtained from bottom-up and top-down approaches have been synthesised and characterised to develop structures based on colloidal self-assemblies. As for sensing applications, the attention was mainly focused on the development of sensors for the food sector. Specifically, a miniaturised impedimetric immunosensor was developed to detect ochratoxin A (OTA) in real food samples, showcasing the ability to identify mycotoxin concentrations within the European Union’s Maximum Residue Levels (MRL). The use of electrochemical impedance spectroscopy (EIS) as detection technique is advantageous because it favours the development of label free immunosensors based on the impedimetric change that occurs when the immunocomplex is formed on the electrode surface. Furthermore, a colorimetric sensor for the determination of phenolic antioxidants, such as caffeic acid, in food products using supramolecular chemistry based on polydiacetylenes (PDAs) complexed with α-cyclodextrins. PDAs are extensively investigated for optical sensing because they easily self-assemble in aqueous media or deposited over surfaces, and their chromatic transition from blue-to-red (also non-fluorescence-to-fluorescence transition) in presence of different stimuli gives the possibility to use them with a label free function. Silver nanoclusters (Ag NCs) are promising materials for the construction of selective and sensitive sensors thanks to their unique optical, physical, and chemical properties. However, stability of Ag NCs in solution is low due to their high surface energy, affinity towards atmospheric oxygen, and strong tendency to agglomerate. Then, a synthetic setup was optimised to obtain stable silver nanoclusters (Ag NCs) for use in nanosensors for mercury detection in water through metallophilic interaction with Hg (Hg2+− Ag+). Turning to nanomaterials for biomedical applications, an enzymatic synthesis was employed to obtain functional polyesters from glycerol and diglycerol, as carriers for drug delivery. Amorphous and amphiphilic poly(diglycerol/glycerol) adipates able to self-assemble in nanostructures were obtained. The effect of the variation of both hydrophilic and hydrophobic segments upon physical properties and drug interactions as well as self-assembly and NPs stability was investigated. A deep physico-chemical characterisation of the systems was carried out. Polymers containing hexandiol demonstrated enhanced features as nanocarriers and have been investigated for their ability to encode enhanced drug loading. The novel materials have shown good biocompatibility in both in vitro and in vivo (whole organism) experiments. Poly(glycerol) adipate (PGA) was also employed alone and blended with poly-L-lactide (PLLA) for the encapsulation of usnic acid (UA), a potent natural compound with various therapeutic properties including antimicrobial and anticancer activities. The development of these carriers aims at investigating the ability of the carriers to increase drug aqueous solubility and reduce hepatotoxicity. PGA blended with PLLA (50/50 weight ratio) assembled to give nanoparticles with a lower size compared to pure polymers. Encapsulation of UA in this system significantly increased UA apparent solubility in water as well as decreased its cytotoxicity. The biological performances of this system were compared to those obtained by employing the natural biopolymer chitosan as carrier for usnic acid. Cross-linked chitosan nanoparticles were obtained by ionic gelation. Interestingly, in this case, not only the hepatotoxicity of the drug was significantly reduced but also a synergistic effect of chitosan in decreasing the invasiveness of osteosarcoma cancer was observed. In the end, a preliminary study has been carried out to use PGA blended with PDAs for bioimaging and tracking, as nanotool alternative to traditional organic dyes. So far, findings from fluorescence microscopy have demonstrated a good internalisation of the nanosystems by the cells, providing new insights into their potential application as tracking materials in molecular bioimaging. Nanosystems are currently being studied using various cancer cell lines.