Point-of-care amperometric determination of L-dopa using an inkjet-printed carbon nanotube electrode modified with dandelion-like MnO2 microspheres

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.

A Sensitive Photoelectrochemical Sensor for Levodopa Detection Using Benzothiadiazole-Based Conjugated Microporous Polymer-Coated Graphene Heterostructures

Since the 1960s, levodopa (LDA) has been the standard drug for treating of Parkinson's disease. In this study, a novel benzothiadiazole-based conjugated microporous polymer-coated graphene heterostructure (CMP-rGO) was synthesized and used to construct a sensitive photoelectrochemical (PEC) sensor capable of detecting LDA. Under optimal experimental conditions, the intensity of the photocurrent produced by the sensor was linear from 0.005 to 40 μM, and the limit of detection of the sensor was 0.0027 μM. The sensor showed good repeatability, stability, and selectivity for LDA detection. Finally, the constructed sensor was used to detect LDA in levodopa tablets, human serum samples, and urine samples and satisfactory results were obtained. Therefore, the PEC sensor provides a novel platform for the detection of LDA in real samples and broadens the applications of conjugated microporous polymers in PEC sensing.

Application of MnO2 Nanorod–Ionic Liquid Modified Carbon Paste Electrode for the Voltammetric Determination of Sulfanilamide

The current work introduced a convenient single-phase hydrothermal protocol to fabricate MnO₂ nanorods (MnO₂ NRs). Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDX) and field-emission scanning electron microscopy (FE-SEM) were used to determine the characteristics of MnO₂ NR. Then, ionic liquid (IL) and MnO₂ NRs were utilized to modify a carbon paste electrode (CPE) surface (MnO₂NR-IL/CPE) to voltammetrically sense the sulfanilamide (SAA). An enhanced voltammetric sensitivity was found for the as-developed modified electrode toward SAA when compared with a bare electrode. The optimization experiments were designed to achieve the best analytical behavior of the SAA sensor. Differential pulse voltammetry (DPV) in the optimized circumstances portrayed a linear dependence on various SAA levels (between 0.07 and 100.0 μM), possessing a narrow detection limit (0.01 μM). The ability of the modified electrode to be used in sensor applications was verified in the determination of SAA present in the actual urine and water specimens, with impressive recovery outcomes.

Electrochemical Determination of Levodopa Using Zinc Sulfide Nanospheres-Reduced Graphene Oxide

Zinc sulfide nanospheres (ZnS NSs) were prepared by hydrothermal synthesis and graphene oxide (GO) was prepared by the Hummer's method. ZnS NSs-rGO/ITO electrode was synthesized by heat treatment at a certain temperature, which was used for the detailed electrochemical determination of levodopa (LD). Finally, they were annealed to form the ZnS NSs-rGO/ITO electrode for detecting levodopa (LD). The results reveal that the ZnS NSs with the diameter of ~1 μm are covered by rGO. The ZnS NSs-rGO/ITO electrode has a good sensitivity of 1.43 μA μM ^-1 for the determination of LD in the concentration range of 1-40 μM. Moreover, it also shows a good selectivity, reproducibility and stability. In order to verify the practicability, we also use the electrode to detect LD in human serum. The detection results also prove that the electrode can be used in real life.

A new sensor based on an amino-montmorillonite-modified inkjet-printed graphene electrode for the voltammetric determination of gentisic acid

An amperometric sensor based on an inkjet-printed graphene electrode (IPGE) modified with amine-functionalized montmorillonite (Mt-NH₂) for the electroanalysis and quantification of gentisic acid (GA) has been developed. The organoclay used as IPGE modifier was prepared and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy, CHN elemental analysis, and thermogravimetry. The electrochemical features of the Mt-NH₂/IPGE sensor were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The sensor exhibited charge selectivity ability which was exploited for the electrochemical oxidation of GA. The GA amperometric response was high in acidic medium (Brinton-Robinson buffer, pH 2) due to favorable interactions between the protonated amine groups and the negatively charged GA. Kinetic studies were also performed by cyclic voltammetry, and the obtained electron transfer rate constant of 11.3 s^-1 indicated a fast direct electron transfer rate of GA to the electrode. An approach using differential pulse voltammetry was then developed for the determination of GA (at + 0.233 V vs. a pseudo Ag/Ag⁺ reference electrode), and under optimized conditions, the sensor showed high sensitivity, a wide working linear range from 1 to 21 μM (R² = 0.999), and a low detection limit of 0.33 μM (0.051 ± 0.01 mg L^-1). The proposed sensor was applied to quantify GA in a commercial red wine sample. The simple and rapid method developed using a cheap clay material could be employed for the determination of various phenolic acids.

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.

A novel selective ternary platform fabricated with MgAl-layered double hydroxide/NiMn2O4 functionalized polyaniline nanocomposite deposited on a glassy carbon electrode for electrochemical sensing of levodopa

In this study, a novel selective electrochemical sensor was fabricated for determination of levodopa (LD) using a glassy carbon electrode modified with MgAl-layered double hydroxide/NiMn₂O₄ functionalized polyaniline nanocomposite (LDH/NMO/PANI) and its successful formation was confirmed by various techniques. Owing to the high surface area and outstanding conductivity features provided by the combination of MgAl-LDH, NiMn₂O₄ and PANI nanoparticles, this ternary nanocomposite exhibited excellent electrochemical activity towards the detection of LD compared with the electrode modified by the pristine MgAl-LDH and MgAl-LDH/NiMn₂O₄ binary nanocomposite. In addition, enormous quantities of amine and imine functional groups on the surface of PANI lead to a strong affinity for attachment to organic molecules such as LD. The ternary nanocomposite modified electrode exhibited excellent analytical parameters such as wide linear response from 0.1 to 100 μM with very low detection limit of 0.005 μM, good reproducibility and long-term stability which are superior among the LD electrochemical sensors. Besides, the constructive sensor possessed acceptable selectivity for recognition of LD in the presence of a variety of potentially interfering species and can also effectively avoid the interference of dopamine (DA) and ascorbic acid (AA). Consequently, the LDH/NMO/PANI/GC electrode was effectively applied to detect LD in human plasma and urine samples with good recoveries, ranging from 98.0-100.1% and it shows potential usage in clinical researches.

Chiral drug fluorometry based on a calix[6]arene/molecularly imprinted polymer double recognition element grafted on nano-C-dots/Ir/Au

A luminescent double recognition nanoprobe is described as a new strategy for the selective determination of chiral molecules. C-dots/Ir/Au fluorescent nanoparticles, synthesised under hydrothermal conditions, are used as a high-performance probe in combination with a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Thiolated calix[6]arene is grafted on C-dots/Ir/Au as the first recognition element, which then forms a host-guest complex with the target molecule levodopa (L-DOPA). Subsequently, an MIP is prepared on the C-dots/Ir/Au (MIP/C-dots/Ir/Au) by chemical polymerisation. After the removal of L-DOPA, double recognition imprinting cavities are formed. The fluorescence intensity at 478 nm of the nanoprobe is effectively quenched by adsorption of L-DOPA on MIP/C-dots/Ir/Au, which provides a method for L-DOPA determination. Owing to the double recognition strategy, this method has excellent selectivity which can effectively avoid interference from enantiomer D-DOPA, and a imprinting factor of 7.1 is obtained for L-DOPA. This accurate and reliable method, with a wide linear range (5 × 10^-10 to 1.2 × 10^-7 mol L^-1) and a low limit of detection (1.45 × 10^-10 mol L^-1), was successfully applied to the determination of L-DOPA in real samples, giving standard recoveries of 89.7-110.0%. Thus, the proposed sensing method provides a viable approach for the determination of a single enantiomer. Graphical abstract Schematic presentation of the MIP/C-dots/Ir/Au for L-DOPA detection. A fluorescence double chiral recognition nanoprobe is prepared of C-dots/Ir/Au nanoparticles as signal probe, and a molecularly imprinted polymer (MIP) and calix[6]arene as a double recognition element. Owing to the double recognition strategy, this method has strong specificity and can effectively avoid interference from enantiomers and racemates.