A fresh strategy based on two-step electrochemical reduction for the fabrication of palladium nanoparticles/reduced oxide nanocomposite-modified glass carbon electrode (PdNPs/rGO/GCE) was established in this study. Field emission scanning electron microscopy (FESEM) images showed that spherical PdNPs were evenly distributed on the surface of rGO-modified electrode (rGO/GCE), and the introduction of PdNPs has no effect on the morphology of rGO. Electrochemical impedance spectroscopy (EIS) studies revealed that the conductivity of PdNPs/rGO/GCE was higher than that of rGO/GCE and bare GCE. The electrochemical performances of PdNPs/rGO/GCE sensor were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry using ascorbic acid (AA), dopamine (DA), and uric acid (UA) as analytes. At the optimized conditions, wide linear ranges of 0.5–3.5 mM (R2 = 0.99), 3–15 μM (R2 = 0.99) and 15–42 μM (R2 = 0.99), and 0.3–1.4 mM (R2 = 0.99) towards AA, DA, and UA in ternary mixture were observed, respectively. In addition to superior anti-interference capability, fast response (≤5 s), excellent reproducibility, and good long-term stability were also given by this sensor. These results suggested that PdNPs/rGO/GCE is promising for the simultaneous detection of AA, DA, and UA in practical application.

In this work, carbon quantum dots (CQDs) were synthesized by microwave irradiation and were electropolymerized on glassy carbon electrode (GCE) to establish an electrochemical sensor for the selective detection of ascorbic acid (AA). Electrochemical behaviors of the prepared sensor were investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Herein, two wide linear responses were obtained in ranges of 0.01-3 mM and 4-12 mM with a low detection limit of 10 μM to AA. High sensitivities (44.13 μA-1 μM-1 cm-2, 9.66 μA-1 μM-1 cm-2, respectively) corresponding to the linear ranges were also achieved. In addition, the electrochemical sensor exhibited good selectivity and robust anti-interference ability toward AA in the presence of dopamine (DA) and uric acid (UA). These results showed that this sensor can be used as a promising tool to detect AA in real complex systems.

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A sensitive and straightforward sensor consisting of a glassy carbon electrode (GCE) containing carbon quantum dots (CQDs), and gold nanoparticles (AuNPs), was fabricated for simultaneous detection of ascorbic acid (AA), dopamine (DA) as well as uric acid (UA). Composite AuNPs/CQDs/GCE and its components were examined using high-resolution transmission and field emission scanning electron microscopies (HRTEM and FESEM, respectively), energy-dispersive and electrochemical impedance (spectroscopies EDS and EIS, respectively), as well as cyclic voltammetry (CV). The synergetic effect, of AuNPs and CQDs provided GCE with an outstanding electrocatalytic rate and excellent selectivity towards AA, DA, and UA oxidation in 0.1M PBS. The linear response ranges of the electrodes were 300-700 and 800-3500 μM for AA, 2-32 μM for DA, and 30-100 and 120-200 μM for UA. The peak potential separation values (ΔEp) of AA-DA, DA-UA, and AA-UA pairs were equal to 150, 130, and 280 mV, respectively. The sensitivity of AuNPs/CQDs/GCE was 0.012 and 0.0057 μA/μM towards AA, 405.13 μA/μM towards DA, as well as 0.148 and 0.044 μA/μM towards UA. Our electrochemical sensor showed excellent stability, analysis reproducibility, and repeatability.