A sensitive and selective electrochemical detection and kinetic analysis of methyl parathion using Au nanoparticle-decorated rGO/CuO ternary nanocomposite

Abstract

Detecting organophosphorus pesticide (OP) residues is essential for maintaining ecological integrity and monitoring public health concerns. This research developed a novel electrochemical sensor that employed composite materials based on copper oxide (CuO) nanostructures and reduced graphene oxide (rGO), customized with Au nanoparticles (AuNPs), to detect methyl parathion (MP) pesticide with high selectivity and sensitivity. The nanocomposite was synthesized in two facile steps, without the use of stabilizers or dispersants, utilizing a simple ultrasonication and photo-reduction process. Morphological analysis revealed a uniform distribution of AuNPs and rGO within the CuO nanostructure. Kinetic studies demonstrated that the electro-reduction of MP on a glassy carbon electrode (GCE) modified with Au@rGO/CuO exhibited irreversible, diffusion-controlled kinetics, with a transfer coefficient (α) value of 0.485. A sensing study employing the square wave voltammetry (SWV) technique exhibited exceptional sensitivity (3.46 μA μM^-1 cm^-2), with a limit of detection (LOD) of 0.045 μM. Moreover, the Au@rGO/CuO-based sensor electrode exhibited exceptional selectivity for MP in the presence of various organic and inorganic species, along with notable reproducibility, repeatability, and stability. Overall, this electrochemical method for effective MP detection suggests that the prepared nanocomposite could contribute to the development of viable electrocatalysts.

Fig. 1. Combined XRD patterns of Au@rGO/CuO, rGO/CuO, and CuO. Standard diffraction cards for Au (JCPDS # 04-0784) and CuO (JCPDS # 45-0937) are included for indexing.

Fig. 2. XPS fine scan spectra of the Au@rGO/CuO nanocomposite: (a) C 1s, (b) O 1s, (c) Cu 2p, and (d) Au 4f.

Fig. 3. SEM image of CuO (a) and Au@rGO/CuO nanocomposite (b). Corresponding EDS compositional analysis for (c) CuO and (d) Au@rGO/CuO.

Fig. 4. TEM image of (a) the Au@rGO/CuO nanocomposite, (b) HR-TEM image of the Au@rGO/CuO nanocomposite, and (c) the SAED pattern of the Au@rGO/CuO nanocomposite.

Fig. 5. Cyclic voltammograms of 2 consecutive cycles at a scan rate of 50 mV s⁻¹ for 30 μm MP in 0.1 M PBS at pH = 7.0, starting from the potential of 0.4 V.

Scheme 1. Proposed electrochemical reaction mechanism.

Fig. 6. Responses of CVs in the presence of 30 μm MP in 0.1 M PBS: (a) bare GCE and CuO/GCE; (b) bare GCE, CuO/GCE, rGO/CuO/GCE, and Au@rGO/CuO/GCE at a scan rate of 50 mV s⁻¹.

Fig. 7. (a) SWV responses of Au@rGO/CuO/GCE at various pH values (5.8–8.8) in 0.1 M PBS buffer with 10 μm MP present, within a potential window of −0.3 V to −0.9 V. (b) The reduction current intensity vs. electrolyte pH. (c) The peak potential fluctuation as a function of the electrolyte pH.

Fig. 8. (a) Voltammograms of Au@rGO/CuO/GCE at 30 μm of MP in 0.1 M PBS (pH 7.0) obtained by varying the scan rate from 5 mV s⁻¹ to 100 mV⁻¹. (b) Correlation between the square root of the scan rate (ν^1/2) and cathodic peak current (I_pc); (c) correlation between log(I_pc) and log scan rate (ν); and (d) linear relationship between cathodic peak potential (E_p) and log ν.

Fig. 9. (a) SWV response of Au@rGO/CuO/GCE in the potential window of −0.3 V to −0.9 V (with a 120 s accumulation time, pulse amplitude of 0.025 V, pulse increment of 0.004 V, and frequency of 15 Hz) as a function of MP concentration in 0.1 M PBS (pH = 7.0). Voltammograms without MP are displayed by the dashed line. (b) Calibration plot of reduction current vs. [MP].

Fig. 10. (a) Selectivity test using SWV responses of Au@rGO/CuO/GCE to 10 μM MP and the concentrations of inorganic interfering species: K₂CO₃, Mg(NO₃)₂, CaCl₂, KCl, and Na₂SO₄ along with organic species: 4-NP, glucose (Glu), sucrose (Suc), chlorpyriphos (Chp), and H₂O₂ at 50 μM. (b) Bar diagram of current response vs. MP and above-mentioned interfering species.