Electrochemical and quantum chemical approaches to the study of dopamine sensing using bentonite and l-cysteine modified carbon paste electrode.

This work presents a significant investigation involving both electrochemical experiment and quantum chemical simulation approaches. The objective was to characterize the electrochemical detection of dopamine (DA). The detection was carried out using a modified carbon paste electrode (CPE) incorporating bentonite (Bent) and l-cysteine (CySH) (named as CySH/Bent/CPE). To understand and explain the oxidation mechanism of DA on the CySH/Bent modified electrode surface, the coupling of the two approaches were exploited. The CySH/Bent/CPE showed excellent electroactivity toward DA such as good sensibility, selectivity, stability, and regenerative ability. The developed sensor shows a dynamic linear range from 0.8 to 80 µM with a limit of detection and quantification of 0.5 µM and 1.5 µM, respectively. During the quantitative analysis of DA in presence of ascorbic acid (AA) and uric acid (UA) the electrochemical oxidation signals of AA, DA, and UA distinctly appear as three separate peaks. The potential differences between the peaks are 190 mv, 150 mv, and 340 mV for the AA-DA, DA-UA, and AA-UA oxidation pairs, respectively. These observations stem from square wave voltammetry (SWV) studies, along with the corresponding redox peak potential separations. The developed sensor is simple and accurate to monitor DA in human serum samples. On the other hand, CySH acts as an electrocatalyst on the CySH/Bent/CPE surface by increasing its active electron transfer sites, as suggested by the quantum chemical modeling with analytical results of Fukui. Furthermore, the voltammetric results obtained agree well with the theoretical calculations.

Detection of paracetamol by a montmorillonite-modified carbon paste sensor: A study combining MC simulation, DFT computation and electrochemical investigations.

This study aims to develop a suitable electrochemical electrode through the incorporation of potassium montmorillonite (MMTK10)clay into the carbon matrix for the direct and sensitive determination of paracetamol (PAR) in pharmaceutical formulations. Electrochemical characterization of the electrodes involves the use of techniques such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). The results reveal that the voltammetric response of PAR is linear over a wide concentration range (1.0-15 µM), with a low detection limit of 0.46 µM. Analytically, PAR recovery results were around 94%, indicating that the developed electrode is highly suitable for PAR detection in pharmaceutical formulation. Additionally, density functional theory (DFT) is employed to investigate the reactivity of PAR and explain the interaction process of PAR on the electrode surface at different pH values. A Monte Carlo simulations model is developed to provide a deeper understanding of the adsorption mechanism, particularly to comprehend molecular interactions and preferential orientations of PAR with MMT fractions at the electrode surface. Reduced Density Gradient is calculated and discussed using techniques such as Multiwfn and Visualization of Molecular Dynamics. The developed CPE-MMTK10 sensor provided a simple preparation method, rapid response, high sensitivity, reproducibility, strong selectivity, and extended stability. Moreover, there is a good correlation between most parameters calculated by DFT and experimental results, thereby reinforcing the validity of the theoretical approach in this study.

A Carbon Paste Electrode Modified by Bentonite and l-Cysteine for Simultaneous Determination of Ascorbic and Uric Acids: Application in Biological Fluids.

A novel modification of a paste carbon electrode by Bentonite (Bent) and l-Cysteine (l-Cyst) was carried out for uric acid (UA) and ascorbic acid (AA) detection and quantification. Morphological and compositional characterization of the electrode surface were carried out using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopic analysis (EDS). Cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques were used to analyze UA and AA. The obtained sensor shows a good stability, sensibility, selectivity, and regeneration ability. Accordingly, the limit of detection (LOD) is found to be 0.031 µm and 9.6 µm for UA and AA, respectively. A good linearity in the range of 0.1 to 100 µm for UA and 10 to 1000 µm for AA was obtained. The peak-to-peak separation of UA-AA (ΔEUA-AA ) was determined to be 330 mV. In addition, the sensor is applied successfully to monitor UA and AA in serum samples.