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Ascorbic acid (AA) determination is of high importance in the diagnosis and treatment of diseases. Herein, we report a new ratiometric electrochemical sensor for ascorbic acid using a glassy carbon electrode (GCE) modified with a copper nanoparticle@resin nanosphere nanocomposite (CuNPs@RNS). The ratiometric strategy was established by immobilizing an internal reference (thionine) on the modified electrode using cyclic voltammetry (CV). The performance of the modified electrodes as well as the newly established ratiometric strategy was explored. The sensing platform had good electrocatalytic ability, reproducibility, and stability. In addition, the ratiometric strategy significantly improved the performance of electrochemical sensing with a wide linear range (0.0837 to 15.5 μM) and a low detection limit of 0.0279 μM under the optimal conditions. The original ratiometric electrochemical sensor was successfully applied to monitor ascorbic acid in tablets and urine. These results showed that the sensor provides a new strategy and broad prospects for biomolecular sensing with reliability and high sensitivity. [ABSTRACT FROM AUTHOR]

The determination of antioxidant capacity, total phenolics, and ascorbic acid using accurate, efficient, low cost, and rapid methods has great analytical importance. The antioxidant capacity, total phenolics, and ascorbic acid content of apricots, arugula, banana, cranberries, spinach, and strawberries were investigated with an electrochemical approach and examined for compatibility with conventional methods. The antioxidant activity was determined by ABTS and DPPH assays. The total phenolic content was determined by the Folin Ciocalteu method and ascorbic acid was quantified by high-performance liquid chromatography (HPLC). In order to perform sensitive and simultaneous electrochemical measurements, the surface of a glassy carbon electrode (GCE) was modified by electropolymerization with p-toluene sulfonic acid (TSA). The TSA/GCE modified sensor was used for the first time for the determination of antioxidant capacity and total phenolic content. The surface of the modified sensor was characterized by cyclic voltammetry and scanning electron microscopy. The TSA/GCE was linearly correlated with the differential pulse voltammetry (DPV) for Trolox and gallic acid in 0.1 M NaNO3 and ascorbic acid in pH 7.4 phosphate buffer. Electrochemical methods offer a promising alternative for the determination of antioxidant capacity and total phenolic content due to their simplicity, rapid response, low cost, sensitivity, and reproducibility. [ABSTRACT FROM AUTHOR]

A surface base polymeric film was fabricated onto a glassy carbon electrode (GCE) via reversible voltammetric scanning in acidic electrolyte containing a (2,4,6-triaminopyrmidine) monomer (TP). The assembled poly(2,4,6-triaminopyrmidine) (PTP) surface material was further modified by electrochemical attachment of tris(2,2'-bipyridine) ruthenium(II) described as Ru(II)-complex. The structure and electrochemical properties of the resulting (Ru-PTP-GCE) surface network were characterized using X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The apparent estimated value of electron transfer rate constant (kapp) of the prepared sensor was three times greater than the virgin PTP. The cooperative effects of the (PTP) and Ru(II)-complex composite increased the efficiency and the stability of the proposed sensor for the selective determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). The detection limit (DL3σ) of DA in this environment was 0.021 μM. The fabricated sensor was successfully applied for DA detection in a blood serum sample with satisfactory recovery. [ABSTRACT FROM AUTHOR]