APPLICATIONS OF ULTRASONICALLY PREPARED COMPOSITE MATERIAL-BASED MODIFIED ELECTRODES IN QUANTITATIVE ANALYSIS

Abstract

This thesis focuses on the development of advanced voltammetric platforms based on nanostructured electrode modifications for the sensitive, selective, and reliable determination of food additives and bioactive compounds in real samples. Three different electrochemical sensors were fabricated by integrating metal oxide nanoparticles with conductive carbon nanomaterials onto glassy carbon electrodes (GCEs), and their analytical performances were thoroughly evaluated. In the first study, a voltammetric system was constructed using multi-walled carbon nanotubes (MWCNTs) and aluminum-doped zinc oxide (AZO) nanoparticles to detect sunset yellow, a widely used food dye. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) confirmed enhanced charge transfer and a significantly increased electroactive surface area at the MWCNTs/AZOmodified electrode. The sensor demonstrated excellent electrocatalytic activity, achieving a linear range of 4.0×10⁻⁹–7.5×10⁻⁶ M and a detection limit (LOD) of 9.5×10⁻¹⁰ M. Successful application to powdered beverages and pharmaceutical syrups validated its accuracy and precision. The second platform, designed for yohimbine determination in dietary supplements and biological samples, utilized graphene nanoplatelets (GN) and indium tin oxide (ITO) to form a high-performance GCE/GN@ITO electrode. The synergistic combination of GN and ITO resulted in improved electrontransfer kinetics, a wide linear range of 4.0×10⁻⁹–2.1×10⁻⁶ M, and an LOD of 5.0×10⁻¹⁰ M, with recovery values close to 100%. Finally, a GCE modified with a graphene nanoplatelets–antimony tin oxide (ATO-GNP) nanocomposite enabled the selective determination of homovanillic acid (HVA), an important neurological biomarker. The ATO-GNP/GCE platform achieved a linear range of 4.0×10⁻⁹–3.5×10⁻⁶ M and an LOD of 4.5×10⁻¹⁰ M, showing strong clinical applicability through accurate measurements in blood and urine samples. Overall, the developed nanocomposite-based electrochemical sensors offer promising potential for practical applications in food safety control, pharmaceutical analysis, and clinical diagnostics.