Nanostructured platform for the sensitive determination of paraoxon by using an electrode modified with a film of graphite-immobilized bismuth

Electrochemical Sensors based on Gold-Silver Core-Shell Nanoparticles Combined with a Graphene/PEDOT:PSS Composite Modified Glassy Carbon Electrode for Paraoxon-ethyl Detection

Herein, a nonenzymatic detection of paraoxon-ethyl was developed by modifying a glassy carbon electrode (GCE) with gold-silver core-shell (Au-Ag) nanoparticles combined with the composite of graphene with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). These core-shell nanoparticles (Au-Ag) were synthesized using a seed-growth method and characterized using UV-vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM) techniques. Meanwhile, the structural properties, surface morphology and topography, and electrochemical characterization of the composite of Au-Ag core-shell/graphene/PEDOT:PSS were analyzed using infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) techniques. Moreover, the proposed sensor for paraoxon-ethyl detection based on Au-Ag core-shell/graphene/PEDOT:PSS modified GCE demonstrates good electrochemical and electroanalytical performance when investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry techniques. It was found that the synergistic effect between Au-Ag core-shell nanoparticles and the composite of graphene/PEDOT:PSS provides a higher conductivity and enhanced electrocatalytic activity for paraoxon-ethyl detection at an optimum pH of 7. At pH 7, the proposed sensor for paraoxon-ethyl detection shows a linear range of concentrations from 0.2 to 100 μM with a limit of detection of 10 nM and high sensitivity of 3.24 μA μM-1 cm-2. In addition, the proposed sensor for paraoxon-ethyl confirmed good reproducibility, with the possibility of being further developed as a disposable electrode. This sensor also displayed good selectivity in the presence of several interfering species such as diazinon, carbaryl, ascorbic acid, glucose, nitrite, sodium bicarbonate, and magnesium sulfate. For practical applications, this proposed sensor was employed for the determination of paraoxon-ethyl in real samples (fruits and vegetables) and showed no significant difference from the standard spectrophotometric technique. In conclusion, this proposed sensor might have a potential to be developed as a platform of electrochemical sensors for pesticide detection.

A novel paraoxon imprinted electrochemical sensor based on MoS2NPs@MWCNTs and its application to tap water samples

Organophosphorus pesticides are widely utilized in agricultural fertility. However, their long-term accumulations result in serious damage to human health and ecological balance. Paraoxon (PAR) can block acetylcholinesterase in the human body, resulting in death. Thus, in this study, a molecularly imprinted electrochemical PAR sensor based on multiwalled carbon nanotubes (MWCNTs)/molybdenum disulfide nanoparticles (MoS₂NPs) nanocomposite (MoS₂NPs@MWCNTs) was proposed for selective tap water determination. A hydrothermal fabrication approach was firstly implemented to prepare MoS₂NPs@MWCNTs nanocomposite. Afterwards, the formation of PAR imprinted electrochemical electrode was performed on nanocomposite modified glassy carbon electrode (GCE) in presence of PAR as template and pyrrole (Py) as a monomer by cyclic voltammetry (CV) technique. Just after determining the physicochemical features of as-fabricated nanostructures by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman spectroscopy, and atomic force microscopy (AFM), the electrochemical behavior of the fabricated sensors was determined through CV, differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The suggested imprinted electrode provided the acceptable limit of quantification (LOQ) and limit of detection (LOD) values of 1.0 × 10^-11 M, and 2.0 × 10^-12 M, respectively. As a consequence, the proposed PAR imprinted electrochemical sensor can be offered for the determining safe tap water and its utility.

Hybrid nanostructures of Pd-WO3 grown on graphitic carbon nitride for trace level electrochemical detection of paraoxon-ethyl

Well-defined crystal structures of Pd-doped WO₃ nanorods were assembled on graphitic carbon sheets (Pd-WO₃/g-C₃N₄) for ultrasensitive detection of paraoxon-ethyl (PEL) using an electrochemical method. The electrochemical behavior of PEL on the Pd-WO₃/g-C₃N₄ hybrid composite was investigated using cyclic voltammetry (CV) and amperometric techniques. The Pd-WO₃ crystallite was seen to modify the kinetics of g-C₃N₄, which improved the reduction/redox peak currents of PEL at the Pd-WO₃/g-C₃N₄ composite compared to those of the g-C₃N₄ and WO₃/g-C₃N₄-modified electrode. Moreover, the π-π interaction and hydrogen bond between the PEL and Pd-WO₃/g-C₃N₄ composite improved the charge-transfer properties. The Pd-WO₃/g-C₃N₄ hybrid composite was therefore able to obtain an enhanced sensitivity (3.70 ± 0.05 μA μM^-1 cm^-2) and low detection limit (0.03 nM; S/N = 3) with a wide range of linear concentrations (0.01-60 and 80-900.0 ± 5 μM) at applied potential of - 0.63 V (vs. Ag/AgCl). The detection of PEL in agricultural water and soil samples was successfully demonstrated with satisfactory RSD of 2.5 to 3.1% and recovery results of 97 to 102%, respectively.

A simple enzymeless approach for Paraoxon determination using imidazole-functionalized carbon nanotubes

This work describes the application of a glassy carbon electrode (GCE) modified with imidazole functionalized carbon nanotubes (CNT-H-IMZ) for Paraoxon (PX) determination in samples of commercial, fresh and 100% orange juice. Homemade multi-walled CNTs were treated according to the Hummers procedure to oxidize graphite and later chemically functionalized with imidazole groups. Modified electrodes with CNT-H-IMZ presented a high peak current of PX reduction and an electrocatalytic effect in comparison to the other electrodes. This behavior was associated with the synergistic contribution of IMZ and CNT that increases the electrochemical activity of PX. Repeatability and reproducibility studies showed that the relative peak current values did not show significant differences between them, less than 10%, and it was possible to define that the diffusional process is the mechanism that limits the electrode mass transport. After the optimization of parameters inherent to the methodology and the voltammetric technique, the proposed device presented a linear region of 1.0 to 16.0 μM^-1 (R² = 0.99), presenting LOD and LOQ as 120 and 400 nM^-1, respectively. The method proposed was successfully applied to PX determination in spiked samples.

A novel, biocompatible and electrocatalytic stearic acid/nanosilver modified glassy carbon electrode for the sensing of paraoxon pesticide in food samples and commercial formulations

A simple, biocompatible and an enzyme-free sensing platform was developed for detection of paraoxon. The surface of a glassy carbon electrode was modified with an electrodeposition of stearic acid/nanosilver composite at -0.7 V for 40 s. The paraoxon undergoes electro-reduction at -550 mV on the modified electrode, and the limits of detection (LOD) was calculated as 0.1 nM (S/N = 3) using differential pulse voltammetry which is lower than that of the existing materials reported. The high stability observed with the modified electrode for prolonging period indicated that the sensitivity of the electrode remains active for several runs of the analysis. The developed analytical strategy was implemented for onion and paddy grain samples and good recovery rates were observed. Also, it was applied for analyzing the purity of the commercial paraoxon sample. The reliability of the developed strategy was confirmed by comparing the results of electrochemical approach with that of HPLC technique.

Surface Molecularly Imprinted Polymer Film with Poly(p-aminothiophenol) Outer Layer Coated on Gold Nanoparticles Inner Layer for Highly Sensitive and Selective Sensing Paraoxon

This paper presents the fabrication of a molecularly imprinted, polymer-based disposable electrochemical sensor for paraoxon (PO) determination. The sensor was based on a screen-printed carbon electrode (SPCE) modified with a surface molecularly imprinted poly (p-aminothiophenol) (PATP)/gold nanoparticles (AuNPs) composite film, which consisted of a PATP outer layer and an AuNPs inner layer. We report a novel strategy, combining surface molecularly imprinting and self-assembly directed electro-polymerization with high densely imprinting PO molecules in the PATP/AuNPs film. Firstly, AuNPs were in situ electrodeposited at the electrode surface, and then assembled with electropolmerizable functional monomer p-aminothiophenol (ATP). Subsequently, PO molecules were assembled onto the ATP monolayer-modified AuNPs, forming a basis of surface molecular imprinting. After that, replenished PO molecules were embedded in the PATP/AuNPs film by PO and the ATP molecular self-assembly directed electro-polymerization in the polymerization precursor mixture. The resulting imprinted PATP/AuNPs/SPCE possesses high sensitivity, affinity, and selectivity toward PO, with a low detection limit of 1 × 10-9 M. The proposed sensor was successfully applied for the determination of PO in fruit and vegetables, giving satisfactory recoveries. The strategy reported herein can be further expected to fabricate various molecular imprinted sensors for the determination of other pesticide residuals.