An ultrasensitive electrochemical sensor based on polydopamine/carboxylic multi-walled carbon nanotubes (MWCNTs−COOH) nanocomposites modified glassy carbon electrode (GCE) was presented in this work, which has been developed for highly selective and highly sensitive determination of an antimicrobial drug, metronidazole. The preparation of polydopamine/MWCNTs–COOH nanocomposites/GCE sensor is simple and possesses high reproducible, where polydopamine can be coated on the surface of MWCNTs–COOH via a simple electropolymerization process. Under optimized conditions, the proposed sensor showed ultrasensitive determination for metronidazole with a wide linear detection range from 5 to 5000 µmol/dm3 and a low detection limit of 0.25 µmol/dm3 (S/N = 3). Moreover, the proposed sensor has been successfully applied for the quantitative determination of metronidazole in real drug samples. This work may provide a novel and effective analytical platform for determination of metronidazole in application of real pharmaceutical and biological samples analysis.

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a b s t r a c tThe simultaneous electrochemical determination of myricetin and rutin remains a challenge due to their indistinguishable potentials. To solve this problem, we constructed a ternary platinum nanoparticle, reduced graphene oxide, multi-walled carbon nanotubes (Pt@r-GO@MWCNTs) nanocomposite via a facile one-pot synthetic method. Under the optimized conditions, the ternary Pt@r-GO@MWCNTs nanocomposite exhibited good electrocatalytic activity toward myricetin and rutin via solid phase extraction and excellent performance for the simultaneous determination of myricetin and rutin. The oxidation peak current of myricetin was proportional to its concentrations in the range of 0.05e50 mM with a detection limit of 0.01 mM (S/N ¼ 3). The linear range for rutin was 0.05e50 mM with a detection limit of 0.005 mM (S/N ¼ 3). The ternary nanocomposite sensor also exhibited good reproducibility and stability, and was successfully used for the simultaneous determination of myricetin and rutin in real orange juice samples with recoveries ranging between 100.57% and 108.46%.

This work reports a highly sensitive electrochemical sensor for the direct detection of pesticides. An electrode modification of silicon carbide nanoparticles has the function of pesticide pre‐concentration by solid‐phase extraction, thus improving the detection sensitivity and simplifying the process of operations. Electrochemical detection of parathion was investigated via cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS), respectively. Under the optimized experimental conditions, the anodic peak currents of parathion by SWV are proportional to the concentrations of parathion in the linearity of Ip (μA)= 0.00325 C (ng/ml) + 0.2162 (R2=0.9985) ranging from 1×10−9 to 1×10−5 ng/ml with a detection limit of 5×10−10 ng/ml (S/N=3). The sensor also exhibits good reproducibility and stability, and has been successfully used for the determination of parathion in real water samples with the recoveries between 99.8% and 101.2%.

We prepared a highly sensitive electrochemical sensor for the free-enzymatic indirect detection of malathion. The electrochemical sensor was based silicon carbide and copper oxide nanocomposite material. The structural and morphological properties of the SiC@CuO-NPs nanocomposite was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). SiC-NPs has the function of malathion preconcentration and SiC@CuO-NPs nanocomposite was noted to possess high affinity towards malathion, thus the redox reaction of CuO could be hindered. This feature was utilized to design as a simple strategy for electrochemical detection of malathion. Electrochemical detection of malathion was investigated via cyclic voltammetry (CV), differential pulse voltammetry (DPV), respectively. Under the optimized experimental conditions, the inhibition rate displays a good linear relationship with the concentration of malathion, the linear range is 0.03 nM ∼ 3.0 nM, and the detection limit is 0.01 nM (S/N = 3). In addition, the sensor exhibits good selectivity, stability and reproducibility, and has been successfully used in the detection of malathion in actual water samples with recoveries between 99.33 % and 106.6 %, which is satisfactory experimental results.