High performance electrochemical method for simultaneous determination dopamine, serotonin, and tryptophan by ZrO2-CuO co-doped CeO2 modified carbon paste electrode

Simultaneous Electrochemical Detection of Dopamine and Tryptophan Using 3D Goethite-Spongin Composites

In this study, a facile approach for simultaneous determination of dopamine (DA) and tryptophan (TRP) using a 3D goethite-spongin-modified carbon paste electrode is reported. The prepared electrode exhibited excellent electrochemical catalytic activity towards DA and TRP oxidation. The electrochemical sensing of the modified electrode was investigated using cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Through differential pulse voltammetry analysis, two well-separated oxidation peaks were observed at 28 and 77 mV, corresponding to the oxidation of DA and TRP at the working electrode, with a large peak separation of up to 490 mV. DA and TRP were determined both individually and simultaneously in their dualistic mixture. As a result, the anodic peak currents and the concentrations of DA and TRP were found to exhibit linearity within the ranges of 4-246 μM for DA and 2 to 150 μM for TRP. The detection limits (S/N = 3) as low as 1.9 μM and 0.37 μM were achieved for DA and TRP, respectively. The proposed sensor was successfully applied to the simultaneous determination of DA and TRP in human urine samples with satisfactory recoveries (101% to 116%).

Eco-friendly synthesis of mesoporous praseodymium oxide nanoparticles for highly efficient electrochemical sensing of carmoisine in food samples

Herein, a mesoporous Pr6O11 nanoparticle (NPs) has been prepared via a simple sonochemical process employing an eco-friendly capping agent, grape juice, and utilized for the development of a novel electrochemical sensor to measure carmoisine. Chronoamperometry, cyclic voltammetry (CV), and differential pulse voltammetry (DPV) have been used for the investigation of the electrochemical behavior of mesoporous Pr6O11/Ionic liquid/Carbon paste electrode (MP-Pr6O11/IL/CPE) in the presence of carmoisine. The oxidation behavior of carmoisine has been examined, and it has been discovered that there was a greater enhancing signal with the MP-Pr6O11/IL/CPE. A lowdetection limit of 12 nM in a linear range of 0.09-135 µM was achieved by the novel carmoisine sensor. Good selectivity, repeatability, stability, and reproducibility were all features of the newly constructed sensor. As a result, the suggested procedurewas appropriate for routine analysis and ought to serve as a viable option for analyzing food colorant.

Unlocking the future of brain research: MOFs, TMOs, and MOFs/TMOs for electrochemical NTMs detection and analysis

The central nervous system relies heavily on neurotransmitters (NTMs), and NTM imbalances have been linked to a wide range of neurological conditions. Thus, the development of reliable detection techniques is essential for advancing brain studies. This review offers a comprehensive analysis of metal-organic frameworks (MOFs), transition metal oxides (TMOs), and MOFs-derived TMOs (MOFs/TMOs) as materials for electrochemical (EC) sensors targeting the detection of key NTMs, specifically dopamine (DA), epinephrine (EP), and serotonin (SR). The unique properties and diverse families of MOFs and TMOs, along with their nanostructured hybrids, are discussed in the context of EC sensing. The review also addresses the challenges in detecting NTMs and proposes a systematic approach to tackle these obstacles. Despite the vast amount of research on MOFs and TMOs-based EC sensors for DA detection, the review highlights the gaps in the literature for MOFs/TMOs-based EC sensors specifically for EP and SR detection, as well as the limited research on microneedles (MNs)-based EC sensors modified with MOFs, TMOs, and MOFs/TMOs for NTMs detection. This review serves as a foundation to encourage researchers to further explore the potential applications of MOFs, TMOs, and MOFs/TMOs-based EC sensors in the context of neurological disorders and other health conditions related to NTMs imbalances.

Preparation of self-supporting vertically/horizontally grown graphene microelectrodes for neurotransmitter determination

The development of microelectrodes for the rapid in situ detection of neurotransmitters and their metabolic levels in human biofluids has considerable significance in biomedical research. In this study, self-supported graphene microelectrodes with B-doped, N-doped, and B- and N-co-doped vertical graphene (BVG, NVG, and BNVG, respectively) nanosheets grown on horizontal graphene (HG) were fabricated for the first time. The high electrochemical catalytic activity of BVG/HG on monoamine compounds was explored by investigating the influence of B and N atoms and the VG layer thickness on the response current of neurotransmitters. Quantitative analysis using the BVG/HG electrode in a blood-like environment with pH 7.4 indicated that the linear concentration ranges were 1-400 and 1-350 μM for dopamine (DA) and serotonin (5-HT), with limits of detection (LODs) of 0.271 and 0.361 μM, respectively. For tryptophan (Trp), the sensor measured a wide linear concentration range of 3-1500 μM over a wide pH range of 5.0-9.0, with the LOD fluctuating between 0.58 and 1.04 μM. Furthermore, the BVG/HG microelectrodes could be developed as needle- and pen-type sensors for the detection of DA, 5-HT, and Trp in human blood and gastrointestinal secretion samples.

Electrochemical detection of carmoisine in the presence of tartrazine on the surface of screen printed graphite electrode modified with nickel-cobalt layered double hydroxide ultrathin nanosheets

Toxic effluents containing azo dyes are discharged from various industries and they adversely affect water resoures, soil, aquatic ecosystems. Also, excessive use of food azo dyes can be carcinogenic, toxic, and adversely affect human health. Therefore, the determination of food azo dyes is significant from the perspective of human health and aquatic organisms. In the present work, nickel-cobalt layered double hydroxide nanosheets were prepared and analyzed by various techniques (field emission-scanning electron microscopy, X-ray diffraction, and fourier Transform-Infrared spectroscopy). Then, the screen printed graphite electrode modified with nickel-cobalt layered double hydroxide nanosheets was used for the detection of carmoisine. The nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode significantly improved the oxidation of carmoisine by increasing the response current and lowering potentials compared to unmodified screen printed graphite electrode. Based on the findings from differential pulse voltammetry, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode sensor response towards carmoisine was linear (0.3-125.0 μM) with a detection limit of 0.09 μM. A sensitivity of 0.3088 μA μM^-1 was achieved. Also, the nickel-cobalt layered double hydroxide nanosheets/screen printed graphite electrode was used for voltammetric detection of carmoisine in the presence of tartrazine. Due to the catalytic activity of prepared layered double hydroxide, the prepared sensor exhibited remarkable separation of the peaks when carmoisine and tartrazine coexist. In addition, the prepared sensor showed good stability. Finally, the proposed sensor had promising applicability for analysis of study analytes in powdered juice and lemon juice, with commendable recoveries between 97.3% and 104.8%.

Nanomaterial-based electrochemical sensors for detection of amino acids

Amino acids are the building blocks of proteins and muscle tissue. They also play a significant role in physiological processes related to energy, recovery, mood, muscle and brain function, fat burning and stimulating growth hormone or insulin secretion. Accurate determination of amino acids in biological fluids is necessary because any changes in their normal ranges in the body warn diseases like kidney disease, liver disease, type 2 diabetes and cancer. To date, many methods such as liquid chromatography, fluorescence mass spectrometry, etc. have been used for the determination of amino acids. Compared with the above techniques, electrochemical systems using modified electrodes offer a rapid, accurate, cheap, real-time analytical path through simple operations with high selectivity and sensitivity. Nanomaterials have found many interests to create smart electrochemical sensors in different application fields e.g. biomedical, environmental, and food analysis because of their exceptional properties. This review summarizes recent advances in the development of nanomaterial-based electrochemical sensors in 2017-2022 for the detection of amino acids in various matrices such as serum, urine, blood and pharmaceuticals.

Surface-Activated Pencil Graphite Electrode for Dopamine Sensor Applications: A Critical Review

Pencil graphite electrode (PGE) is an alternative, commercially available, ready-to-use, screen-printed electrode for a wide range of electroanalytical applications. Due to the complex-matrix composition and unpredictable electro-inactive nature of PGE in its native form, a surface pre-treatment/activation procedure is highly preferred for using it as an electroactive working electrode for electroanalytical applications. In this article, we review various surface pre-treatment and modification procedures adopted in the literature with respect to the sensitive and selective detection of dopamine as a model system. Specific generation of the carbon-oxygen functional group, along with partial surface exfoliation of PGE, has been referred to as a key step for the activation. Based on the Scopus^® index, the literature collection was searched with the keywords "pencil and dopamine". The obtained data were segregated into three main headings as: (i) electrochemically pre-treated PGE; (ii) polymer-modified PGEs; and (iii) metal and metal nanocomposite-modified PGE. This critical review covers various surface activation procedures adopted for the activation for PGE suitable for dopamine electroanalytical application.

Ce3+/Ce4+-Doped ZrO2/CuO Nanocomposite for Enhanced Photocatalytic Degradation of Methylene Blue under Visible Light

In recent years, photocatalysis has been used as an environmentally friendly method for the degradation of organic pigments in water. In this study, Ce³⁺/Ce⁴⁺-doped ZrO₂/CuO as a mixed semiconductor oxide was successfully prepared by a one-step hydrothermal method. The Ce³⁺/Ce⁴⁺-doped ZrO₂/CuO has shown high degradation efficiency of methylene blue (MB), and the maximum degradation percentage was observed to be 94.5% at 180 min under irradiation visible light. The photocatalytic activity increases significantly by doping Ce³⁺/Ce⁴⁺ in ZrO₂/CuO for MB degradation. Ce³⁺/Ce⁴⁺ doping is shown to reduce the (e^-/h⁺) recombination rate and improve the charge transfer, leading to enhanced photocatalytic activity of materials. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR, EDS, BET and diffuse reflectance spectroscopy (DRS).

Hydroxyapatite/L-Lysine Composite Coating as Glassy Carbon Electrode Modifier for the Analysis and Detection of Nile Blue A

An amperometric sensor was developed by depositing a film coating of hydroxyapatite (HA)/L-lysine (Lys) composite material on a glassy carbon electrode (GCE). It was applied for the detection of Nile blue A (NBA). Hydroxyapatite was obtained from snail shells and its structural properties before and after its combination with Lys were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analyses. The coupling of Lys to HA was attributed to favorable interaction between negatively charged -COO^- groups of Lys and divalent ions Ca²⁺ of HA. Electrochemical investigations pointed out the improvement in sensitivity of the GCE/Lys/HA sensor towards the detection of NBA in solution. The dependence of the peak current and potential on the pH, scan rate, and NBA concentration was also investigated. Under optimal conditions, the GCE/Lys/HA sensor showed a good reproducibility, selectivity, and a NBA low detection limit of 5.07 × 10^-8 mol L^-1. The developed HA/Lys-modified electrode was successfully applied for the detection of NBA in various water samples.