Electrochemical behavior of l-dopa at single-wall carbon nanotube-modified glassy carbon electrodes

Rapid and selective colorimetric determination of L-DOPA in human serum with silver nanoparticles

L-DOPA, or l-3,4-dihydroxyphenylalanine is an aromatic amino acid, which plays a significant role in human metabolism as a precursor of important neurotransmitters. We develop a fast and simple colorimetric method for the detection of L-DOPA in biological fluids. The method is based on the reduction of silver ions with L-DOPA and the subsequent formation of L-DOPA stabilized silver nanoparticles (Ag NPs). In this novel approach, L-DOPA works as both reducing and stabilizing agent, which provides selectivity and simplifies the procedure. HR-TEM images show very narrow Ag NPs distribution with an average size of 24 nm. Such sensor design is suggested for the first time. We also calculate vertical ionization potential, vertical electron affinity, and Gibbs free energy change of different ionic forms of L-DOPA and amino acids at the M06-2X/def2-TZVP level for the gas phase in comparison with that of silver. A model of silver ions reduction by aromatic amino acids is proposed: the ionic forms with charge -1 are suggested to reduce silver ions. High selectivity against aromatic amino acids, dopamine and serotonin is achieved by tuning pH and involving two L-DOPA forms with charged both hydroxyphenolate and carboxylate groups in the stabilization of uniform-sized Ag NPs. The method is applicable for the determination of L-DOPA in human serum with the 50 nM limit of detection and the linear range up to 5 μM. Ag NPs formation and coloring the solution proceeds in a few minutes. The suggested colorimetric method has potential application in clinical trials.

Electroanalytical Overview: The Determination of Levodopa (L-DOPA)

L-DOPA (levodopa) is a therapeutic agent which is the most effective medication for treating Parkinson's disease, but it needs dose optimization, and therefore its analytical determination is required. Laboratory analytical instruments can be routinely used to measure L-DOPA but are not always available in clinical settings and traditional research laboratories, and they also have slow result delivery times and high costs. The use of electroanalytical sensing overcomes these problems providing a highly sensitivity, low-cost, and readily portable solution. Consequently, we overview the electroanalytical determination of L-DOPA reported throughout the literature summarizing the endeavors toward sensing L-DOPA, and we offer insights into future research opportunities.

Additively Manufactured Rotating Disk Electrodes and Experimental Setup

This manuscript details the first report of a complete additively manufactured rotating disk electrode setup, highlighting how high-performing equipment can be designed and produced rapidly using additive manufacturing without compromising on performance. The additively manufactured rotating disk electrode system was printed using a predominantly acrylonitrile butadiene styrene (ABS) based filament and used widely available, low-cost electronics, and simplified machined parts to create. The additively manufactured rotating disk electrode system costs less than 2% of a comparable commercial solution (£84.47 ($102.26) total). The rotating disk electrode is also additively manufactured using a carbon black/polylactic acid (CB/PLA) equivalent, developing a completely additively manufactured rotating disk electrode system. The electrochemical characterization of the additively manufactured rotating disk electrode setup was performed using hexaamineruthenium(III) chloride and compared favorably with a commercial glassy carbon electrode. Finally, this work shows how the additively manufactured rotating disk electrode experimental system and additive manufactured electrodes can be utilized for the electroanalytical determination of levodopa, a drug used in the treatment of Parkinson’s disease, producing a limit of detection of 0.23 ± 0.03 μM. This work represents a step-change in how additive manufacturing can be used in research, allowing the production of high-end equipment for hugely reduced costs, without compromising on performance. Utilizing additive manufacturing in this way could greatly enhance the research possibilities for less well-funded research groups.

Gold-Platinum Core-Shell Nanoparticles with Thiolated Polyaniline and Multi-Walled Carbon Nanotubes for the Simultaneous Voltammetric Determination of Six Drug Molecules

In this proof-of-concept study, a novel nanocomposite of the thiolated polyaniline (tPANI), multi-walled carbon nanotubes (MWCNTs) and gold–platinum core-shell nanoparticles (Au@Pt) (tPANI-Au@Pt-MWCNT) was synthesized and utilized to modify a glassy carbon electrode (GCE) for simultaneous voltammetric determination of six over-the-counter (OTC) drug molecules: ascorbic acid (AA), levodopa (LD), acetaminophen (AC), diclofenac (DI), acetylsalicylic acid (AS) and caffeine (CA). The nanocomposite (tPANI-Au@Pt-MWCNT) was characterized with transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Using the sensor (GCE-tPANI-Au@Pt-MWCNT) in connection with differential pulse voltammetry (DPV), the calibration plots were determined to be linear up to 570.0, 60.0, 60.0, 115.0, 375.0 and 520.0 µM with limit of detection (LOD) of 1.5, 0.25, 0.15, 0.2, 2.0, and 5.0 µM for AA, LD, AC, DI, AS and CA, respectively. The nanocomposite-modified sensor was successfully used for the determination of these redox-active compounds in commercially available OTC products such as energy drinks, cream and tablets with good recovery yields ranging from 95.48 ± 0.53 to 104.1 ± 1.63%. We envisage that the electrochemical sensor provides a promising platform for future applications towards the detection of redox-active drug molecules in pharmaceutical quality control studies and forensic investigations.

Wearable Electrochemical Microneedle Sensor for Continuous Monitoring of Levodopa: Toward Parkinson Management

Levodopa is the most effective medication for treating Parkinson's disease (PD). However, because dose optimization is currently based on patients' report of symptoms, which are difficult for patients to describe, the management of PD is challenging. We report on a microneedle sensing platform for continuous minimally invasive orthogonal electrochemical monitoring of levodopa (L-Dopa). The new multimodal microneedle sensing platform relies on parallel simultaneous independent enzymatic-amperometric and nonenzymatic voltammetric detection of L-Dopa using different microneedles on the same sensor array patch. Such real-time orthogonal L-Dopa sensing offers a built-in redundancy and enhances the information content of the microneedle sensor arrays. This is accomplished by rapid detection of L-Dopa using square-wave voltammetry and chronoamperometry at unmodified and tyrosinase-modified carbon-paste microneedle electrodes, respectively. The new wearable microneedle sensor device displays an attractive analytical performance with the enzymatic and nonenzymatic L-Dopa microneedle sensors offering different dimensions of information while displaying high sensitivity (with a low detection limit), high selectivity in the presence of potential interferences, and good stability in artificial interstitial fluid (ISF). The attractive analytical performance and potential wearable applications of the microneedle sensor array have been demonstrated in a skin-mimicking phantom gel as well as upon penetration through mice skin. The design and attractive analytical performance of the new orthogonal wearable microneedle sensor array hold considerable promise for reliable, continuous, minimally invasive monitoring of L-Dopa in the ISF toward optimizing the dosing regimen of the drug and effective management of Parkinson disease.

Detection of the neurotransmitter dopamine by a glassy carbon electrode modified with self-assembled perovskite LaFeO3 microspheres made up of nanospheres

Glassy carbon electrode modified with LaFeO₃ microspheres made up of nanospheres and having high electrocatalytic ability to detect the neurotransmitter dopamine.

Synthesis of ZnO nanorods and their application in the construction of a nanostructure-based electrochemical sensor for determination of levodopa in the presence of carbidopa

A novel carbon paste electrode modified with ZnO nanorods and 5-(4′-amino-3′-hydroxy-biphenyl-4-yl)-acrylic acid (3,4′-AAZCPE) was fabricated.

Thermodynamic parameters of electrochemical oxidation of L-DOPA: experimental and theoretical studies

Electrode potential and thermodynamic parameters of the electrochemical reaction of L-DOPA in aqueous solution are obtained experimentally by cyclic voltammetry method and also calculated theoretically using accurate ab initio calculations (G3MP2//B3LYP) along with the available solvation model of CPCM. The pH dependence of the redox activity of L-DOPA in aqueous solution at temperatures in the range of 10-30 °C was used for the experimental determination of the standard reduction potential, changes of entropy, enthalpy, and Gibbs free energy for the studied reaction. The experimental formal redox potential of the two-proton-two-electron reduction process was obtained to be 0.745 V versus standard hydrogen electrode (SHE). The theoretical and experimental values (0.728 and 0.745 V) for the standard electrode potential of L-DOPA are in agreement with each other. The difference between the peak potential of the L-DOPA and the products, which are produced by chemical reactions, has been measured experimentally and also calculated theoretically. There is also an agreement between experimental and theoretical potential difference. Also in this work, the changes of thermodynamic functions of solvation are calculated from the differences between the solution-phase experimental values and the gas-phase theoretical values.

Electrochemical Detection of Iron in a Lixiviant Solution of Polluted Soil Using a Modified Glassy Carbon Electrode

This paper presents preliminary results on the modification of glassy carbon electrodes with Multiwall Carbon Nanotubes with or without Polyaniline and Pt nanoparticles as electrocatalytic materials for metallic pollutants detection. Electrodes were constructed and incorporated as amperometric detectors of ionic iron electroreduction using the Flow Injection Amperometric technique in aqueous solution. The results not only revealed the modified electrode with nanotubes, polyaniline and platinum nanoparticles were the most selective and sensitive, but also provided an electroanalytic tool to analyze iron in lixiviated samples of polluted soil. The proposed iron sensor exhibited a linear response between 0 and 10 mM with detection and quantification limits of 0.003 and 0.012 μM, respectively. The aqueous samples were taken from a lixiviated solution of polluted soil from Mineral de Pozos, Guanajuato, Mexico, to define the erosion grade of soil.

Direct electrochemistry and voltammetric determination of midecamycin at a multi-walled carbon nanotube coated gold electrode

Macrolide antibiotics generally shows slow electron-transfer rate and produces insensitive redox peaks at conventional electrodes. In this paper, we studied the electrochemical behavior of midecamycin, one of macrolide antibiotics, at a multi-walled carbon nanotube (MWNT) modified gold electrode. It was found that MWNT could adsorb midecamycin and promote its direct electron-transfer. Hence midecamycin exhibited a more sensitive anodic peak at the modified electrode. The electrochemical process showed the feature of a mixed-control system of diffusion and adsorption. Under the optimized conditions (i.e. pH 7.0 phosphate supporting electrolyte, 5 μl 0.5 mg ml⁻¹ multi-walled carbon nanotube suspension for Ø = 2.0 mm electrode, accumulation at -0.8 V for 150 s), the anodic peak current was linear to midecamycin concentration in the range of 5 × 10⁻⁷ to 2 × 10⁻⁵M, with a correlation coefficient of 0.998. For a 5×10⁻⁶ M midecamycin solution, ten repetitive measurements gave a relative standard deviation of 2.2%. This method was successfully applied to the determination of midecamycin in medicine tablet and the recovery was 97.5-104.0%.

Determination of l-dopa using electropolymerized 3,3′,3″,3‴-tetraaminophthalocyanatonickel(II) film on glassy carbon electrode

Electropolymerized film of 3,3',3'',3'''-tetraaminophthalocyanatonickel(II) (p-Ni(II)TAPc) on glassy carbon (GC) electrode was used for the selective and stable determination of 3,4-dihydroxy-L-phenylalanine (L-dopa) in acetate buffer (pH 4.0) solution. Bare GC electrode fails to determine the concentration of L-dopa accurately in acetate buffer solution due to the cyclization reaction of dopaquinone to cyclodopa in solution. On the other hand, p-Ni(II)TAPc electrode successfully determines the concentration of L-dopa accurately because the cyclization reaction was prevented at this electrode. It was found that the electrochemical reaction of L-dopa at the modified electrode is faster than that at the bare GC electrode. This was confirmed from the higher heterogeneous electron transfer rate constant (k(0)) of L-dopa at p-Ni(II)TAPc electrode (3.35 x 10(-2) cms(-1)) when compared to that at the bare GC electrode (5.18 x 10(-3) cms(-1)). Further, it was found that p-Ni(II)TAPc electrode separates the signals of ascorbic acid (AA) and L-dopa in a mixture with a peak separation of 220 mV. Lowest detection limit of 100 nM was achieved at the modified electrode using amperometric method. Common physiological interferents like uric acid, glucose and urea does not show any interference within the potential window of L-dopa oxidation. The present electrode system was also successfully applied to estimate the concentration of L-dopa in the commercially available tablets.