Carbon nanomaterials such as carbon dots (0D), carbon nanotubes (1D), graphene (2D), and graphite (3D) have been exploited as electrode materials for various applications because of their high surface-active area,...
Flavin adenine dinucleotide (FAD) is a coenzyme and acts as a redox cofactor in metabolic process. Owing to such problems as poor electron transfer properties, unfavorable adsorption, and lack of stability on rigid electrodes, the bio-electrochemical applications of FAD have been limited. Herein, a novel fabrication method was developed for the immobilization process using 2D MXene (Ti3C2Tx), which enhanced the redox property of FAD and improved the electro-catalytic reduction of hydrogen peroxide (H2O2) in neutral medium. The FAD-immobilized Ti3C2Tx electrode (FAD/Ti3C2Tx) was studied by UV-Visible and Raman spectroscopies, which confirmed the successful adsorption of FAD on the Ti3C2Tx surface. The surface morphology and the elemental composition of Ti3C2Tx were investigated by high resolution transmission electron microscopy and the energy dispersive X-ray analysis. The redox property of the FAD/Ti3C2Tx modified glassy carbon electrode (FAD/Ti3C2Tx/GCE) was highly dependent on pH and exhibited a stable redox peak at −0.455 V in neutral medium. Higher amounts of FAD molecules were loaded onto the 2D MXene (Ti3C2Tx)-modified electrode, which was two times higher than the values in the reported work, and the surface coverage (ᴦFAD) was 0.8 × 10−10 mol/cm2. The FAD/Ti3C2Tx modified sensor showed the electrocatalytic reduction of H2O2 at −0.47 V, which was 130 mV lower than the bare electrode. The FAD/Ti3C2Tx/GCE sensor showed a linear detection of H2O2 from 5 nM to 2 µM. The optimization of FAD deposition, amount of Ti3C2Tx loading, effect of pH and the interference study with common biochemicals such as glucose, lactose, dopamine (DA), potassium chloride (KCl), ascorbic acid (AA), amino acids, uric acid (UA), oxalic acid (OA), sodium chloride (NaCl) and acetaminophen (PA) have been carried out. The FAD/Ti3C2Tx/GCE showed high selectivity and reproducibility. Finally, the FAD/Ti3C2Tx modified electrode was successfully applied to detect H2O2 in ovarian cancer cell lines.
Reduced form of β‐nicotinamide adenine dinucleotide (NADH) and its oxidized form (NAD+) are the main cofactors involved in more than 300 dehydrogenase reactions. NAD+ is one of the important oxidizing agent for the oxidation of alcohol, aldehyde and ketones. Similarly, NADH has been used for the treatment of Alzheimer and Parkinson's diseases. Herein, we have reported synthesis of graphene flakes by electrochemical exfoliation of graphite in sodium tungstate solution. It was found that tungstate (WO42−) and hydroxyl (OH−) ions were intercalated into graphite layers and enabled the production of graphene flakes. As‐obtained graphene flakes were characterized by UV‐Visible (UV‐Vis), Fourier transform infrared (FT‐IR), Raman, Field emission scanning electron microscopy (FE‐SEM), Energy dispersive X‐ray (EDX) and High‐resolution transmission electron microscopies (HR‐TEM). FT‐IR, Raman and EDX analysis were confirmed that tungstate (WO42−) ions were present on the surface of graphene flakes. Moreover, graphene‐WO42− (Gr−W) dispersion was prepared by probe‐sonication to form a thin‐film on the surface of glassy carbon electrode (Gr−W/GCE). Interestingly, Gr‐W modified GCE reduced the overpotentials of NADH oxidation and NAD+ reduction. This new senor was also showed linear responses for NADH and NAD+ from 10–270 μM and 100–500 μM, respectively. Furthermore, the selectivity of the Gr−W/GCE was tested in the presence of L‐tyrosine, L‐isoleucine, L‐alanine, glutathione, dopamine (DA), ascorbic acid (AA), uric acid (UA), oxalic acid (OA), glucose, hydrogen peroxide (H2O2), acetaminophen (PA), potassium chloride (KCl) and sodium chloride (NaCl). It was found that selective detection of both NADH and NAD+ could be achieved by using Gr−W/GCE. Finally, the real application of the sensor was demonstrated by accurately detecting spiked NADH concentrations in human blood serum. The recovery analysis was also confirmed that Gr−W/GCE could be useful to detect NADH in biological samples.
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