Carbon Electrodes Coated with TiO2–Cu-MOF Composites for Nonenzymatic Detection of Ascorbic Acid

Noninvasive and real-time monitoring of antioxidants such as ascorbic acid is essential in clinical diagnostics and food quality control. In this study, 3D-structured titanium dioxide (TiO₂)-integrated copper-based metal–organic frameworks (Cu-MOF) composite was coated onto carbon paper (CP) via the doctor blade method and employed as the sensing electrode in an extended gate field effect transistor (EGFET) configuration for ascorbic acid detection. The morphological analysis was carried out by high-resolution scanning electron microscope (HR-SEM) and high-resolution transmission electron microscope (HR-TEM), revealing that the 3D-structured, densely packed TiO₂ nanorods (∼16 nm in diameter) were integrated with octahedral Cu-MOF microstructures, further confirming the successful integration. The effective surface area of TiO₂–Cu-MOF/CP was estimated to be 48 cm². The sensing electrode (TiO₂–Cu-MOF/CP) achieved an limit of detection (LOD) of 12 nM and a wide detection range from 15 nM to 14.38 mM for ascorbic acid detection, with a sensitivity of 193.44 μA μM^–1 cm^–2. Additionally, the sensing electrode demonstrated good selectivity to interference from other mixed interfering molecules such as uric acid, dopamine, and glucose. In addition to the EGFET studies, Scanning Kelvin probe (SKP) measurements were performed to investigate the influence of ascorbic acid adsorption on the surface potential of the working electrode. The synergistic role of hierarchically structured TiO₂–Cu-MOF nanostructures enables an effective detection of ascorbic acid, which was further validated in real sample analysis using commercial pulpy orange juice.