Selective determination of -DOPA at a graphene oxide/yttrium oxide modified glassy carbon electrode

Eu2O3@Cr2O3 Nanoparticles-Modified Carbon Paste Electrode for Efficient Electrochemical Sensing of Neurotransmitters Precursor L-DOPA

There are ten million people in the world who have Parkinson's disease. The most potent medicine for Parkinson's disease is levodopa (L-DOPA). However, long-term consumption of L-DOPA leads to the appearance of side effects, as a result of which the control and monitoring of its concentrations are of great importance. In this work, we have designed a new electrochemical sensor for detecting L-DOPA using a carbon paste electrode (CPE) modified with Eu₂O₃@Cr₂O₃ composite nanoparticles. Rare earth elements, including Eu, are increasingly used to design new electrode nanocomposites with enhanced electrocatalytic properties. Europium has been considered a significant lanthanide element with greater redox reaction behavior. We conducted a hydrothermal synthesis of Eu₂O₃@Cr₂O₃ and, for the first time, the acquired nanoparticles were used to modify CPE. The proposed Eu₂O₃@Cr₂O₃/CPE electrode was investigated in terms of its electrocatalytic properties and then used to develop an analytical method for detecting and quantifying L-DOPA. The proposed sensor offers a wide linear range (1-100 µM), high sensitivity (1.38 µA µM^-1 cm^-2) and a low detection limit (0.72 µM). The practical application of the proposed sensor was investigated by analyzing commercially available pharmaceutical tablets of L-DOPA. The corresponding results indicate the excellent potential of the Eu₂O₃@Cr₂O₃/CPE sensor for application in real-time L-DOPA detection.

Electrochemical Analysis of Sulfisoxazole Using Glassy Carbon Electrode (GCE) and MWCNTs/Rare Earth Oxide (CeO2 and Yb2O3) Modified-GCE Sensors

In this work, new electrochemical sensors based on the modification of glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs)-rare metal oxides (REMO) nanocomposites were fabricated by drop-to-drop method of MWCNTs-REMO dispersion in ethanol. REMO nanoparticles were synthesized by precipitation followed by hydrothermal treatment at 180 °C in absence and presence of Triton^TM X-100 surfactant. Cyclic voltammetry (CV) analysis using MWCNTs-CeO₂@GCE and MWCNTs-Yb₂O₃@GCE sensors were used for the analysis of sulfisoxazole (SFX) drug in water samples. The results of CV analysis showed that MWCNTs-REMO@GCE sensors have up to 40-fold higher sensitivity with CeO₂ compared to the bare GCE sensor. The estimated values of the limit of detection (LoD) of this electrochemical sensing using MWCNTs-CeO₂@GCE and MWCNTs-Yb₂O₃@GCE electrodes reached 0.4 and 0.7 μM SFX in phosphate buffer pH = 7, respectively. These findings indicate that MWCNTs-REMO@GCE electrodes are potential sensors for analysis of sulfonamide drugs in water and biological samples.

Voltammetric Determination of Levodopa Using Mesoporous Carbon-Modified Screen-Printed Carbon Sensors

Levodopa is a precursor of dopamine, having important beneficial effects in the treatment of Parkinson’s disease. In this study, levodopa was accurately detected by means of cyclic voltammetry using carbon-based (C-SPCE), mesoporous carbon (MC-SPCE) and ordered mesoporous carbon (OMC-SPCE)-modified screen-printed sensors. Screen-printed carbon sensors were initially used for the electrochemical detection of levodopa in a 10⁻³ M solution at pH 7.0. The mesoporous carbon with an organized structure led to better electroanalysis results and to lower detection and quantification limits of the OMC-SPCE sensor as compared to the other two studied sensors. The range of linearity obtained and the low values of the detection (0.290 µM) and quantification (0.966 µM) limit demonstrate the high sensitivity and accuracy of the method for the determination of levodopa in real samples. Therefore, levodopa was detected by means of OMC-SPCE in three dietary supplements produced by different manufacturers and having various concentrations of the active compound, levodopa. The results obtained by cyclic voltammetry were compared with those obtained by using the FTIR method and no significant differences were observed. OMC-SPCE proved to be stable, and the electrochemical responses did not vary by more than 3% in repeated immersions in a solution with the same concentration of levodopa. In addition, the interfering compounds did not significantly influence the peaks related to the presence of levodopa in the solution to be analyzed.

A novel flow injection amperometric sensor based on carbon black and graphene oxide modified screen-printed carbon electrode for highly sensitive determination of uric acid

A simple, rapid, and cost-effective flow injection amperometric (FI-Amp) sensor for sensitive determination of uric acid (UA) was developed based on a new combination of carbon black (CB) and graphene oxide (GO) modified screen-printed carbon electrode (SPCE). The CB-GO nanocomposites were simply synthesized and modified on the working electrode surface to increase electrode conductivity and enhance the sensitivity of UA determination via the electrocatalytic activity toward UA oxidation. The morphologies and electrochemical properties of the synthesized nanomaterials were investigated through scanning electron microscopy (SEM), transmission electron microscopy (TEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The modified electrode was incorporated with FI-Amp to improve UA detection's sensitivity, stability, and automation. Some parameters affecting sensitivity were optimized, including pH of the electrolyte solution, applied potential, amount of CB-GO suspension, flow rate, injection volume, and reaction coil length. Using an applied potential of +0.35 V (vs Ag/AgCl), the anodic current was linearly proportional to UA concentration over the range of 0.05-2000 μM with a detection limit of 0.01 μM (3 S/N). Besides, the developed method provides a sample throughput of 25 injections h^-1, excellent sensitivity (0.0191 μA/μM), selectivity, repeatability (RSD 3.1%, n = 7), and stability (RSD 1.08%, n = 50). The proposed system can tolerate potential interferences commonly found in human urine. Furthermore, a good correlation coefficient between the results obtained from the FI-Amp sensor and a hospital laboratory implies that the proposed system is accurate and can be utilized for UA detection in urine samples.

Polypyrrole merged zirconium-based metal-organic framework NU-1000 for detection of levodopa

A post-synthetic integration of polypyrrole onto NU-1000 MOF (PPy@NU-1000) was done by pyrrole adsorption, followed by oxidative polymerization. The synthesized materials were characterized by XRD, SEM, BET, and FTIR. The ultra-high specific surface area with high-density catalytic sites of NU-1000 (2223 m² g^-1) was combined with the electrical conductivity of PPy (2-100 S cm^-1). PPy@NU-1000 provides superior electrocatalytic activity and charge transfer properties compared to an individual component. The PPy@NU-1000-modified GCE was applied to detect the biomolecule Levodopa (LD). The DPV oxidation peak of LD was strongest at 272 ± 10 mV vs. Ag/AgCl reference electrode. Under the optimized experimental condition, the fabricated electrochemical sensor exhibited a wide quantification range of 0.005-70 μM with a sub-nanomolar detection limit of 0.0001 μM (S/N 3). The described sensor exhibits high sensitivity (2.08 μA μM^-1 cm^-2) with reasonable stability, reproducibility, and selectivity for the detection LD in the presence of potentially interfering compounds. Furthermore, human serum analysis showed excellent recovery values within the range 99.3-101.6%. Validation of the method was performed against HPLC.Graphical abstract.

Synthesis of La2O3/MWCNT nanocomposite as the sensing element for electrochemical determination of theophylline

In this study, an electrochemical sensor was applied for the determination of theophylline, a bronchodilator drug, using differential pulse voltammetry (DPV). A glassy carbon electrode (GCE) surface was modified with the La2O3/MWCNT nanocomposite. The design is simplistic, efficient, greener and solvent-free microwave procedure for synthesizing La2O3/MWCNT nanocomposites. Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques are used to characterize the features of the La2O3/MWCNT nanocomposite morphology and structure. The use of the modified sensor remarkably enhanced the current density and displayed a linear response ranging between 0.1 and 400.0 μM, with a limit of detection of 0.01 μM (S/N = 3). Using optimized conditions, the modified sensor demonstrated very good stability, selectivity and improved accuracy. Acceptable outputs were achieved in the analysis of real specimens, indicating that it is possible to use the modified sensor for practical analyses.

Engineering two-dimensional metal oxides via surface functionalization for biological applications

Schematic illustration of 2D MO nanosheets for applications in biosystems.

Green and facile microwave solvent-free synthesis of CeO2 nanoparticle-decorated CNTs as a quadruplet electrochemical platform for ultrasensitive and simultaneous detection of ascorbic acid, dopamine, uric acid and acetaminophen

This study designed a simplistic, efficient, and greener procedure to synthesize CeO₂-CNTs. The analysis of structural and morphological characteristics of nano-composites has been done with regard to different procedures (e.g., EDX, XRD, & FESEM). In addition, simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen (AC) has been examined at the modified glassy carbon electrode with CeO₂-CNTs nano-composites. The surface area and electron transfer speed of the interplay between neuro-transmitters and electrode may be efficiently enhanced due to the existence of CeO₂ nano-particles on CNTs surfaces. Moreover, electro-chemical behavior of electrodes has been dealt with by differential pulse voltammetry (DPV), impedance analysis (EIS), and cyclic voltammetry (CV). Acceptable linear response of AA, DA, UA and AC respectively have been ranged 0.01-900.0 μM, 0.01-700.0 μM, 0.01-900.0 μM, and 0.01-900.0 μM with determination limits (S/N = 3) of 3.1 nM, 2.6 nM, 2.4 nM and 4.4 nM. Ultimately, this procedure was used with successful results for determining AA, DA, UA and AC in real specimens, which suggested probable uses in other sensing studies.