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This study reports facile synthesis of MnO2 nanoflowers/N-doped reduced graphene oxide (MnO2NFs/NrGO) composite and its application on the simultaneous determination of dopamine (DA) and uric acid (UA). The microstructures, morphologies, and electrochemical performances of MnO2NFs/NrGO were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), respectively. The electrochemical experiments showed that the MnO2NFs/NrGO composites have the largest effective electroactive area and lowest charge transfer resistance. MnO2NFs/NrGO nanocomposites displayed superior catalytic capacity toward the electro-oxidation of DA and UA due to the synergistic effect from MnO2NFs and NrGO. The anodic peak currents of DA and UA increase linearly with their concentrations varying from 0.2 μM to 6.0 μM. However, the anodic peak currents of DA and UA are highly correlated to the Napierian logarithm of their concentrations ranging from 6.0 μM to 100 μM. The detection limits are 0.036 μM and 0.029 μM for DA and UA, respectively. Furthermore, the DA and UA levels of human serum samples were accurately detected by the proposed sensor. Combining with prominent advantages such as facile preparation, good sensitivity, and high selectivity, the proposed MnO2NFs/NrGO nanocomposites have become the most promising candidates for the simultaneous determination of DA and UA from various actual samples.

The development of sensitive and stable electrochemical sensors toward dopamine is highly desirable. Herein, a novel voltammetric sensor was developed for the detection of dopamine using shuttle-like α-Fe 2 O 3 nanoparticles/electro-reduced graphene oxide nanocomposites (S-Fe 2 O 3 /ErGO). The surface morphology, microstructure, and chemical composition of S-Fe 2 O 3 /ErGO nanocomposites were investigated by SEM, XRD and Raman spectra, respectively. The electrochemical behavior of Fe 2 O 3 /ErGO nanocomposite modified glass carbon electrode (S-Fe 2 O 3 /ErGO/GCE) was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results show that S-Fe 2 O 3 /ErGO nanocomposites have large electrochemical active area and low charge transfer resistance. The anodic peak current of S-Fe 2 O 3 /ErGO/GCE increases 1-fold and 37-fold compared to that of ErGO/GCE and S-Fe 2 O 3 /GCE, respectively, suggesting the remarkably synergistic enhancement effect on the electrooxidation of dopamine. The anodic peak current is proportional to the concentration of dopamine over the range of 0.01 μM-2 μM. However, the logarithm of anodic peak current versus logarithm of dopamine concentration is linearly related in the range of 2 μM-80 μM. The detection limit (3σ/s) and sensitivity are estimated to be 1.15 nM and 95.57 μA μM −1 cm −1 , respectively. Moreover, S-Fe 2 O 3 /ErGO/GCE also showed good anti-interference, reproducibility and stability. Finally, the proposed S-Fe 2 O 3 /ErGO/GCE was successfully employed to determinate dopamine in the human serum samples with satisfactory results.

Various morphologies of iron oxide nanoparticles (Fe2O3 NPs), including cubic, thorhombic and discal shapes were synthesized by a facile meta-ion mediated hydrothermal route. To further improve the electrochemical sensing properties, discal Fe2O3 NPs with the highest electrocatalytic activity were coupled with graphene oxide (GO) nanosheets. The surface morphology, microstructures and electrochemical properties of the obtained Fe2O3 NPs and Fe2O3/GO nanohybrids were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. As expected, the electrochemical performances were found to be highly related to morphology. The discal Fe2O3 NPs coupled with GO showed remarkable electrocatalytic activity toward the oxidation of dopamine (DA) and uric acid (UA), due to their excellent synergistic effect. The electrochemical responses of both DA and UA were linear to their concentrations in the ranges of 0.02–10 μM and 10–100 μM, with very low limits of detection (LOD) of 3.2 nM and 2.5 nM for DA and UA, respectively. Moreover, the d-Fe2O3/GO nanohybrids showed good selectivity and reproducibility. The proposed d-Fe2O3/GO/GCE realized the simultaneous detection of DA and UA in human serum and urine samples with satisfactory recoveries.

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