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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]

A simple electrochemical sensor for epinephrine (EP) has been developed by modification of a carbon film electrode (CFE) with multiwalled carbon nanotubes (MWCNTs) in a chitosan matrix. Cyclic voltammetry (CV) was employed for the evaluation of the electrochemical oxidation of EP at modified electrodes MWCNT/CFE in different pH electrolytes. Under the optimum conditions (pH 7.0), the MWCNT/CFE electrode showed significant electrocatalytic oxidation of EP: a decrease of about 200 mV in the overpotential and an 11-fold increase in the peak current, compared with the unmodified CFE. Detection of EP was carried out by CV, fixed potential amperometry, and differential pulse voltammetry (DPV); the most sensitive response with the lowest detection limit of 0.9 µM obtained by DPV with preconcentration. At MWCNT/CFE, a separation of 175 mV between EP and ascorbic acid peaks was found. The sensor exhibited excellent stability over a period of 6 months and was successfully applied to the analysis of injectable adrenaline solutions. [ABSTRACT FROM AUTHOR]

A carbon paste electrode (CPE), modified with novel hydroquinone/TiO2 nanoparticles, was designed and used for simultaneous determination of ascorbic acid (AA), uric acid (UA) and folic acid (FA). The magnitude of the peak current for modified TiO2-nanoparticle CPE (MTNCPE) increased sharply in the presence of ascorbic acid and was proportional to its concentration. A dynamic range of 1.0-1400.0 μM, with the detection limit of 6.4 × 10-7 M for AA, was obtained using the DPV technique (pH = 7.0). The prepared electrode was successfully applied for the determination of AA, UA, and FA in real samples. [ABSTRACT FROM AUTHOR]