Development of Metal-Organic Frameworks (MOFs) based Electrochemical Sensors for the Detection of Glucose

Abstract

Electrochemical detection techniques have gained significant interest in monitoring glucose levels, detecting cancer, and identifying infectious diseases and biological warfare agents. These techniques have various benefits, including low cost, simplicity, high level of sensitivity, low energy requirements, show good performance even in the turbid sample, and also have direct control systems. Despite these benefits, the development of electrochemical biosensors is still a challenge. Among other materials used in electrochemical sensing, Metal-Organic Frameworks (MOFs) exhibit remarkable potential as a novel class of hybrid materials. MOFs are characterized by their porous nature, which provides them with large surface areas and pore volumes. Moreover, their excellent thermal and chemical stability further enhances their appeal for electrochemical sensing applications. Therefore, MOFs represent a promising pathway for developing advanced sensing materials. In addition, integrating heterogeneous nanostructured materials into MOFs accelerates the development of advanced electrochemical sensors. Furthermore, MOFs composites have been recognized as ideal platforms to host functional materials, such as conducting nanoparticles. This makes MOFs a perfect material for electrochemical sensing compared to their pristine form, leading to improved electrocatalytic performance. Consequently, electrochemical sensing of environmental and biochemical targets has been made more efficient with the development of MOF composite-based devices. The present dissertation highlights the significance of MOFs and nanocomposites in biosensor applications for electrochemical sensing. This dissertation describes the design and fabrication of Ag@TiO2@ZIF-67 and Indium MOF-derived Ag@In2O3 non-enzymatic electrochemical glucose sensors. The objective was to develop electrochemical biosensors with high sensitivity and low detection limits for selective glucose detection across a wide concentration range. For this purpose, nanocomposites were deposited on their surface, specifically Ag@TiO2@ZIF-67, on a Glassy Carbon Electrode (GCE) and Indium MOF-derived Ag@In2O3 on Nickel Foam to enhance the electrode performance. The structural properties of functionalized electrodes are assessed through X-ray diffraction with Cu-Kα radiation at 2θ values ranging from 5° to 80°. Scanning Electron Microscopy (SEM) was used to analyze the electrode materials' morphology. For the electrochemical experiments, a Gamry Potentiostat was used at ambient temperature. The prepared materials on GCE and Nickel Foam were used as working electrodes, the platinum wire was used as a counter electrode, and Ag/AgCl was used as a reference electrode in a three-electrode configuration. It was determined that the oxidation of glucose was a diffusion-controlled process. The reaction was electrochemically reversible, involving the spontaneous adsorption of glucose on the electrode surface. The Ag@TiO2@ZIF-67 on GCE and Indium MOF-derived Ag@In2O3 on Nickel Foam sensors were efficiently used to determine glucose in 0.1 M NaOH electrolyte solution. The non-enzymatic electrochemical sensors were highly selective toward glucose in the presence of other biological interfering agents. The lowest glucose detection limit was achieved at 0.99 µM from Ag@TiO2@ZIF-67 and 0.49 µM from MOF-derived Ag@In2O3. Nevertheless, the Ag@TiO2@ZIF-67 on GCE and MOF-derived Ag@In2O3 on Nickel Foam sensors were suitable for monitoring glucose at concentrations (i.e., 4-7mM) typical for human blood serum. In conclusion, the electrochemical biosensors explored in this Ph.D. study demonstrated high sensitivity and selectivity for glucose detection in the presence of other interfering species. The results revealed that the performance of these electrochemical sensors is primarily influenced by the enhanced catalytic and conductive properties of MOFs when combined with nanostructured materials. The novel nanomaterial-based platforms proposed in this dissertation provide a promising foundation for developing high-performing electrochemical sensors for medical diagnostic applications.