Zr-MOF Materials for Electrochemical Sensing: From Solvothermal Microstructures to PLAL-Derived Nanoparticles

The aim of this thesis is to develop a zirconium-based metal-organic framework (Zr-MOF), based on nanostructured materials, using a combination of chemical and physical techniques for electrochemical sensing applications. At the early stage of this PhD project, the research focused on the development of nanostructured materials based on zirconia, graphene oxide (GO), and silver nanoparticles (AgNPs), which were synthesized using different techniques and combined to form binary and ternary nanocomposites (ZrO2/GO, ZrO2/AgNPs, and GO/AgNPs). These materials were used to modify screen-printed carbon electrodes (SPCEs) for electrochemical sensing applications in both environmental and biomedical fields. The promising performance of these systems led to the publication of three peer-reviewed papers, which are included in the appendices of this thesis. Building on these findings, the research direction was extended toward zirconium-based metal-organic frameworks (Zr-MOFs), particularly UiO-67, due to their superior porosity and crystalline structure. Two additional manuscripts, currently under submission, focus on UiO-67/SPCE systems, including both microstructured and Pulsed Laser Ablation in Liquid (PLAL)-derived nanostructured materials, as well as laser-irradiated UiO-67 powders dispersed in water. These studies systematically investigate the electrochemical detection of selected biomarkers using all synthesized samples. Specifically, Zr-MOFs were employed as receptor materials to modify screen-printed carbon electrodes (SPCEs) for the sensitive and selective detection of biologically relevant analytes, particularly D-tyrosine (D-Tyr). Initially, three water-stable Zr-MOFs, namely UiO-66, UiO-67, and MOF-808, were synthesized via a solvothermal method and subsequently characterized using various physicochemical techniques. These materials were integrated onto SPCEs via drop-casting, and their electrochemical performance was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV). All modified electrodes demonstrated effective electroanalytical performance toward dopamine (DA), uric acid (UA), and D-Tyr, with clear peak separation enabling simultaneous detection. Among them, UiO-67/SPCE exhibited the best performance for D-Tyr sensing, achieving the highest sensitivity (0.1406 μA·μM−1) and the lowest limit of detection (LOD = 0.72 μM) in the linear range of (0.5-200 μM). The sensor also showed good selectivity, strong anti-interference capability, and reliable performance in complex biological matrices such as bovine serum (LOD = 0.45 μM; recovery ≈ 103.87%). Building on these results, UiO-67 was further engineered using PLAL, a clean and versatile physical technique. PLAL was applied as a top-down approach to produce MOF-nanostructured colloids. Unlike conventional chemical synthesis, this method enables the production of pure, stable, and ligand-free colloidal nanoparticles. Laser ablation in water was performed on MOF targets prepared by mechanically pressing the as-synthesized powder. The resulting colloids were further sonicated to reduce particle size and prevent aggregation, yielding the A1 and A2 samples. A direct comparison between microstructured and PLAL-derived nanostructured UiO-67/SPCE electrodes revealed significant performance enhancement at the nanoscale. The A1/SPCE electrode exhibited the best electroanalytical performance, with improved sensitivity (0.1666 μA·μM−1) and enhanced detection capability (LOD = 1.29 μM over 0-200 μM and 0.06 μM at low concentrations). Furthermore, PLAL-derived electrodes exhibited higher current responses than the microstructured UiO-67/SPCE. Selectivity was also enhanced, with A1/SPCE enabling clear resolution of D-Tyr, DA, and UA, including a distinguishable UA signal not observed for the microstructured electrode. Additionally, controlled irradiation studies demonstrated that moderate laser power (0.2 W, S6) optimizes electrochemical performance compared with higher-power irradiation (0.5 W, S8) or non-irradiated (reference) samples (S14). Overall, the physicochemical properties of Zr-MOF-based materials, particularly UiO-67, were systematically investigated, revealing that their high surface area and tunable nanostructure provide numerous active sites for analyte interaction, thereby significantly improving sensitivity and lowering detection limits. PLAL-derived MOF nanocolloids exhibit an optimal combination of surface area, molecular selectivity, and electrochemical activity, making them highly suitable for fast, sensitive, and selective electrochemical biosensing applications.