TOWARD ENHANCED BIMODAL SENSING: TIO₂-COATED METALLIC NANOSTRUCTURES FOR ELECTROCHEMICAL ANDPHOTOELECTROCHEMICAL DETECTION

This thesis presents a study on the synthesis, modification, and optimization of titanium dioxide (TiO₂) thin films for electrochemical and photoelectrochemical sensing applications. After preparing TiO₂ films via a sol-gel process, using titanium isopropoxide as a precursor, a systematic investigation of sol aging revealed a strong dependence between aging duration and the properties of the resulting film. Among the conditions analyzed, a period of 14 days produced the best results, with more homogeneous films, more uniform surface coverage, and a significantly increased photocurrent response. These results confirmed the importance of sol aging as a key parameter in modulating the properties of TiO₂. To expand the system's functionality, the films were subsequently modified with gold nanoparticles (AuNPs) synthesized using wet chemical methods. The aim was to evaluate the influence of metal nanostructures on the behavior of the material. It emerged that TiO₂ plays a crucial role in stabilizing the nanoparticles: in the absence of the oxide layer, the AuNPs show poor adhesion and rapid dissolution, while the TiO₂ coating preserves their structural integrity. The TiO₂/AuNP hybrid system showed improved electrochemical performance, allowing the detection of ciprofloxacin, an antibiotic, even in the presence of common interferents, confirming the synergy between metal nanoparticles and the TiO₂ matrix. Given the decisive role of nanoparticles, research then turned to alternative techniques for their manufacture. Although widespread, chemical methods in solution have limitations such as low structural stability, poor control of surface distribution, and complex synthesis procedures. To overcome these critical issues, a physical approach based on solid state dewetting was adopted. In this method, a thin metal film is deposited by sputtering onto a conductive substrate and then heated to induce the formation of nanoparticles. This technique has made it possible to obtain uniform and stable nanostructures, with dimensions that can be adjusted by varying the initial thickness of the metal film. The interaction between TiO₂ and metal nanoparticles was subsequently studied by depositing a layer of TiO₂ on top of the gold nanostructures. As expected, the insulating nature of TiO₂ reduced the electrochemical sensitivity of the electrodes. However, the introduction of TiO₂ conferred new properties on the system, including photoactivity. This feature was exploited for the photoelectrochemical detection of hydrogen peroxide (H₂O₂), demonstrating that the same device can operate via two distinct mechanisms: electrochemical (EC) and photoelectrochemical (PEC). This dual functionality was defined as bimodality. Based on this bimodal approach, a new device was developed combining TiO₂ with silver nanostructures. The aim was to evaluate the effect of replacing gold with silver and to verify the feasibility of bimodality in a context closer to real-world applications. In this configuration, TiO₂ enabled PEC oxidation thanks to its photoactivity, while silver facilitated the electrochemical reduction of the target molecule, the antihistamine cetirizine, thanks to its known catalytic activity. The integration of the two materials produced a synergistic effect: the device allowed PEC and EC measurements to be performed with the same electrode and the same experimental setup, while improving stability and reusability. The analytical parameters obtained—sensitivity, detection limit, and reproducibility—were satisfactory for both techniques. Furthermore, the ability to compare two independent signals increased the reliability of the measurements. This dual-channel strategy proved particularly effective in mitigating the effect of interferents, which often affect one technique but not the other. Overall, the work demonstrates the potential of TiO₂-based hybrid systems as versatile, stable, and high-performance platforms for chemical sensing. Through systematic material optimization and the development of bimodal strategies, the thesis makes significant contributions to the design of multifunctional devices capable of addressing real-world analytical challenges.