Simultaneous determination of hydroxylamine and phenol using a nanostructure-based electrochemical sensor

Self-assembled ordered AuNRs-modified electrodes for simultaneous determination of dopamine and topotecan with improved data reproducibility

Gold nanomaterials have been widely explored in electrochemical sensors due to their high catalytic property and good stability in multi-medium. In this paper, the reproducibility of the signal among batches of gold nanorods (AuNRs)-modified electrodes was investigated to improve the data stabilization and repeatability. Ordered and random self-assembled AuNRs-modified electrodes were used as electrochemical sensors for the simultaneous determination of dopamine (DA) and topotecan (TPC), with the aim of obtaining an improved signal stability in batches of electrodes and realizing the simultaneous determination of both substances. The morphology and structure of the assemblies were analyzed and characterized by UV-Vis spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). Electrochemical studies showed that the ordered AuNRs/ITO electrodes have excellent signal reproducibility among several individuals due to the homogeneous mass transfer in the ordered arrangement of the AuNRs. Under the optimized conditions, the simultaneous detection results of DA and TPC showed good linearity in the ranges 1.75-45 μM and 1.5-40 μM, and the detection limits of DA and TPC were 0.06 μM and 0.17 μM, respectively. The results showed that the prepared ordered AuNR/ITO electrode had high sensitivity, long-term stability, and reproducibility for the simultaneous determination of DA and TPC, and it was expected to be applicable for real sample testing.

Recent Advantages of Mediator Based Chemically Modified Electrodes; Powerful Approach in Electroanalytical Chemistry

Background:

Modified electrodes have advanced from the initial studies aimed at understanding electron transfer in films to applications in areas such as energy production and analytical chemistry. This review emphasizes the major classes of modified electrodes with mediators that are being explored for improving analytical methodology. Chemically modified electrodes (CMEs) have been widely used to counter the problems of poor sensitivity and selectivity faced in bare electrodes. We have briefly reviewed the organometallic and organic mediators that have been extensively employed to engineer adapted electrode surfaces for the detection of different compounds. Also, the characteristics of the materials that improve the electrocatalytic activity of the modified surfaces are discussed.

Objective:

Improvement and promotion of pragmatic CMEs have generated a diversity of novel and probable strong detection prospects for electroanalysis. While the capability of handling the chemical nature of the electrode/solution interface accurately and creatively increases , it is predictable that different mediators-based CMEs could be developed with electrocatalytic activity and completely new applications be advanced.

Properties and Recent Advantages of N,N’-dialkylimidazolium-ion Liquids Application in Electrochemistry

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N,Nʹ-dialkylimidazolium-ion liquids is one of the important ionic liquids with a wide range of application as conductive electrolyte and in electrochemistry. The modified electrodes create a new view in fabrication of electroanalytical sensors. Many modifiers have beeen suggested for modification of electroanalytical sensor since many years ago. Over these years, ionic liquids and especially room temperature ionic liquids have attracted more attention due to their wide range of electrochemical windows and high electrical conductivity. N,Nʹ-dialkylimidazolium-ion liquids are one of the main important ionic liquids suggested for modification of bare electrodes and especially carbon paste electrodes. Although many review articles have reported onthe use of ionic liquids in electrochemical sensors, no review article has been specifically introduced so far on the review of the advantages of N,Nʹ-dialkylimidazolium ionic liquid. Therefore, in this review paper we focused on the introduction of recent advantages of N,Nʹ-dialkyl imidazolium ionic liquid in electrochemistry.

A simple immunosensor for thyroid stimulating hormone

Determination of thyroid-stimulating hormone (TSH) level in serum or plasma is defined as a sensitive method for the diagnosis of hyperthyroidism and hypothyroidism and also in many diseases thought to be related to TSH levels. In this study, a novel simple impedimetric immunosensor based on polyamidoamine dendrimer was developed. Anti TSH antibody was immobilized on the gold electrode by using cysteamine self-assembled monolayer strategy. In constructing the immunosensor, a polyamidoamine dendrimer was used to increase the surface area in which Antı-TSH was immobilized and glutaraldehyde was used as a cross-linker. After each immobilization step, the electrode surface was monitored by electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy and energy-dispersive X-ray spectroscopy techniques and optimization studies were performed. The reproducibility, repeatability, linearity and sensitivity of the immunosensor were examined. Also, the interference experiments for glucose, salts and proteins in serum were performed. The limit of detection and limit of quantification values of the proposed immunosensor were 0.026 mIUL^-1 and 0.086 mIUL^-1, respectively and it was able to detect the amount of TSH within a linear range of 0.1-0.6 mIUL^-1.

Enticing 3D peony-like ZnGa2O4 microstructures for electrochemical detection of N, N-dimethylmethanamide chemical

We demonstrate the hydrothermal synthesis of three dimension (3D) peony-like morphology of zinc gallate (ZnGa₂O₄), dominated by assembled nanosheets and applied as electrode material in electrochemical detection of N,N-dimethylmethanamide chemical. The crystalline, structural and compositional characterizations deduced the formation of high quality ZnGa₂O₄ with spinal crystal structure. Peony-like 3D ZnGa₂O₄ was benefited by a high surface area of ~62.3 m² g^-1, good pore distribution (mean pore diameter of ~23.3 nm) and large pore volume of ~0.3622 cm³ g^-1. N,N-dimethylmethanamide chemical sensor based on peony-like 3D ZnGa₂O₄ electrode presented a linear curve in the working dynamic range of 1 nM-10 mM. Significantly improved chemical sensitivity of ~154.2 mA mM^-1 cm^-2 with low detection limit value of ~0.14 μM were achieved. The fabricated sensor based on peony-like 3D ZnGa₂O₄ electrode endorsed real sample analysis and ascertained the selectivity towards N,N-dimethylmethanamide chemical by analyzing a range of interfering analytes, viz. ethanol, tetrahydrofuran, methyl amine chemical.

A portable selective electrochemical sensor amplified with Fe3O4@Au-cysteamine-thymine acetic acid as conductive mediator for determination of mercuric ion

Mercury ion (Hg²⁺) is considered to be one of the most toxic heavy metal ions and can cause adverse effects on kidney function, the central nervous system, and the immune system. Therefore, it is important to develop a fast and simple method for sensitive and selective detection of Hg²⁺ in the environment. This research proposes a portable electrochemical sensor for rapid and selective detection of Hg²⁺. The sensor platform is designed based on thymine acetic acid anchored with cysteamine-conjugated core shell Fe₃O₄@Au nanoparticles (Fe₃O₄@Au/CA/T-COOH) immobilized on a sensing area of a screen-printed carbon electrode (SPCE) with the aid of an external magnetic field embedded in a homemade electrode holder for ease of handling. In the presence of Hg²⁺, the immobilized thymine combines specifically with Hg²⁺ and forms a thymine-Hg²⁺-thymine mismatch (T-Hg²⁺-T). The resulting amount of Hg²⁺ was determined by differential pulse anodic stripping voltammetry (DPASV). Under optimal conditions, the sensor exhibited two wide linearities in a range from 1 to 200 μg L^-1 and 200-2200 μg L^-1 with the reliability coefficient of determination of 0.997 and 0.999, respectively. The detection limit (LOD) and the quantification limit (LOQ) were also determined to be 0.5 μg L^-1 and 1.0 μg L^-1, respectively. The sensor was further applied for determination of Hg²⁺ in water samples, a certified reference material and fish samples. The results were compared with flow injection atomic spectroscopy-inductively coupled plasma-optical emission spectroscopy (FIAS-ICP-OES) systems as a reference method. Results obtained with the proposed sensor were relatively satisfactory, and they showed no significant differences at a 95% confidence level by t-test from the standard method. Therefore, considering its fast and simple advantages, this novel strategy provides a potential platform for construction of a Hg²⁺ electrochemical sensor.

A Screen-Printed Electrode Modified With Graphene/Co3O4 Nanocomposite for Electrochemical Detection of Tramadol

In this paper, graphene (Gr)/Co₃O₄ nanocomposite was synthesized and utilized for the development of a novel electrochemical sensor to detect tramadol. Tramadol determination was examined by linear sweep voltammetry, differential pulse voltammetry, cyclic voltammetry, and chronoamperometry on Gr/Co₃O₄ nanocomposite-modified screen-printed electrode (Gr/Co₃O₄/SPE) in phosphate-buffered saline (PBS). Under the optimized condition, the detection limit of tramadol is 0.03 μM (S/N = 3) in the linear ranges of 0.1–500.0 μM. Furthermore, Gr/Co₃O₄/SPE was satisfactorily utilized to detect tramadol in tramadol tablet and urine specimens.

N,N'-Diphenylthiourea electrochemical sensor for the detection of l-glutamate and Aspartate in beef

This study was conducted to design an electrochemical sensor for detection of l-glutamate (L-Glu) and Aspartate (Asp), which contribute largely to the umami taste of beef. Using N, N'-diphenylthiourea (DPTU), polypyrrole (PPy), and polyvinyl chloride (PVC), a composite electrode (DPTU/PVC/PPy/Pt) was prepared for rapidly electrochemical detection of l-Glu and Asp. The surface morphology of the synthesized functionalized electrode was characterized by Field Emission Scanning Electron Microscopy (FESEM). Potentials of umami amino acids accounted for 97.8%, while six interferential amino acids existed. The linear correlation between the content of l-Glu and Asp in beef broth was studied under different treatment conditions. The sensor compared with an amino acid analyzer well detected the contents of l-Glu and Asp in beef broths, with a coefficient of 0.991 in Pearson correlation analysis and an accuracy of 88.9%. The proposed electrochemical sensor showed good concurrence with previously reported methods and was effectively employed for the quantification of l- Glu and Asp in beef. PRACTICAL APPLICATION: The sensor exhibits the good performance with high stability and high accuracy. And it is a potential sensing platform with good reproducibility, making the proposed method suitable and reliable for routine analysis of L-Glu and Asp in beef. This method was proved promising for quantitative detecting amino acids in beef.

Fully-printed electrochemical sensors made with flexible screen-printed electrodes modified by roll-to-roll slot-die coating

The manufacture of sensors using large-scale production techniques, such as roll-to-roll (R2R) processing, may fulfill requirements of low-cost disposable devices. Herein, we report the fabrication of fully-printed electrochemical sensors using screen-printed carbon electrodes coated with carbon black inks through slot-die coating within an R2R process. As a proof of concept, sensors were produced to detect the neurotransmitter dopamine with high reproducibility and low limit of detection (0.09 μmol L^-1). Furthermore, fully-printed biosensors made with a tyrosinase-containing ink were used to detect catechol in natural water samples. Since slot-die deposition enables printing enzymes without significant activity loss, the biosensors exhibited high stability over a period of several weeks. Even more important, R2R slot-die coating may be extended to any type of sensors and biosensors with the possibility of large-scale manufacturing.

Developments and applications of nanomaterial-based carbon paste electrodes

This review summarizes the progress that has been made in the past ten years in the field of electrochemical sensing using nanomaterial-based carbon paste electrodes. Following an introduction into the field, a first large section covers sensors for biological species and pharmaceutical compounds (with subsections on sensors for antioxidants, catecholamines and amino acids). The next section covers sensors for environmental pollutants (with subsections on sensors for pesticides and heavy metal ions). Several tables are presented that give an overview on the wealth of methods (differential pulse voltammetry, square wave voltammetry, amperometry, etc.) and different nanomaterials available. A concluding section summarizes the status, addresses future challenges, and gives an outlook on potential trends.

This review summarizes the progress that has been made in the past ten years in the field of electrochemical sensing using nanomaterial-based carbon paste electrodes.

A High-Performance Liquid Chromatography Method for Determination of Genotoxic Impurity Hydroxylamine in Drug Substances

Hydroxylamine (NH2OH) is widely used in pharmaceutical intermediates and final drug substances synthesis. Since hydroxylamine is a well-known genotoxic impurity compound that needs to be controlled down to ppm level in pharmaceutical compounds. It is very difficult to detect using conventional analytical techniques due to its physical-chemical properties like the lack of chromophore, low molecular weight, the absence of carbon atom and high polarity. In addition to that, the analysis of the pharmaceutical samples encounters considerable obstruction from matrix components that greatly overshadow the response of hydroxylamine. This report describes a simple, selective and sensitive high-performance liquid chromatography (HPLC)-UV derivatization method for the determination of hydroxylamine in drug substances. The HPLC method was detected up to 0.01 ppm of hydroxylamine with S/N > 3.0 and quantified up to 0.03 ppm of hydroxylamine with S/N ratio > 10.0. This validated method can be applied as a generic method to detect the hydroxylamine for pharmaceutical process control and drug substance release.

A Simple and Direct LC-MS Method for Determination of Genotoxic Impurity Hydroxylamine in Pharmaceutical compounds

Hydroxylamine is a known genotoxic impurity compound that needs to be controlled down to ppm level in pharmaceutical processes. It is difficult to detect using conventional analytical techniques due to its physio-chemical properties like lack of chromophore, low molecular weight, absence of carbon atom and high polarity. In addition to that, analysis of the pharmaceutical samples encounters considerable obstruction from matrix components that greatly overshadow the response of hydroxylamine. This study describes a simple, sensitive and direct Liquid Chromatographic-Mass Spectrometric method (LC-MS) for detection of hydroxylamine in pharmaceutical compounds. The LC-MS method was detected up to 0.008 ppm of hydroxylamine with S/N > 3.0 and quantified up to 0.025 ppm of hydroxylamine with S/N ratio >10.0. This validated method can be applied as a generic method to detect the hydroxylamine for pharmaceutical process control and drug substance release.

Fabrication of Highly Sensitive and Stable Hydroxylamine Electrochemical Sensor Based on Gold Nanoparticles and Metal-Metalloporphyrin Framework Modified Electrode

This paper describes the immobilization of gold nanoparticles on metal-metalloporphyrin frameworks (AuNPs/MMPF-6(Fe)) through electrostatic adsorption. The composites were characterized by powder X-ray diffraction, zeta potential, transmission electron microscopy, electrochemical impedance spectroscopy, and voltammetric methods. MMPF-6(Fe) exhibited a pair of redox peaks of the Fe(III)TCPP/Fe(II)TCPP redox couple. The AuNPs/MMPF-6(Fe)-based electrochemical sensor demonstrates a distinctly higher electrocatalytic response to the oxidation of hydroxylamine due to the synergic effect of the gold metal nanoparticles and metal-metalloporphyrin matrix. The voltammetric current response exhibits two linear dynamic ranges, 0.01-1.0 and 1.0-20.0 μmol L(-1), and the detection limit was as low as 0.004 μmol L(-1) (S/N = 3). Moreover, the biosensor exhibits high reproducibility and stability in acid solution. Our work not only offers a simple way to achieve the direct electrochemical behavior of metalloporphyrin but also expands the potential applications of MOFs-based composites in bioanalysis.

Surface molecularly imprinted electrochemical sensor for phenol based on SiO2 nanoparticles

A novel surface molecularly imprinted electrochemical sensor for the recognition and detection of phenol was constructed. It has a specific recognition ability for phenol over other phenolic compounds for real samples with excellent repeatability.

Fabrication of novel TiO2 nanoparticles/Mn(III) salen doped carbon paste electrode: application as electrochemical sensor for the determination of hydrazine in the presence of phenol

Hydrazine and phenol are two important environmental pollutants. In this work, an electrochemical sensor for the selective and sensitive detection of hydrazine in presence of phenol was developed by the bulk modification of carbon paste electrode (CPE) with TiO2 nanoparticles and Mn(III) salen. Large peak separation, good sensitivity, and stability allow this modified electrode to analyze hydrazine individually and simultaneously along with phenol. Applying square wave voltammetry (SWV), a linear dynamic range of 3 × 10(-8)-4.0 × 10(-4) M with detection limit of 10.0 nM was obtained for hydrazine. Finally, the proposed method was applied to the determination of hydrazine and phenol in some real samples.

Construction of a nanostructure-based electrochemical sensor for voltammetric determination of bisphenol A

A novel carbon paste electrode modified with graphene oxide nanosheets and an ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) was fabricated. The electrochemical study of the modified electrode, as well as its efficiency for voltammetric oxidation of bisphenol A, is described. The electrode was also employed to study the electrochemical oxidation of bisphenol A, using cyclic voltammetry, chronoamperometry, square wave voltammetry and electrochemical impedance spectroscopy as diagnostic techniques. Square wave voltammetry exhibits a linear dynamic range from 9.0 × 10(-8) to 2.5 × 10(-4) M and a detection limit of 55.0 nM for bisphenol A. Finally, this new sensor was used for determination of bisphenol A in water samples using the standard addition method.

Electrochemical determination of hydrazine using a ZrO2 nanoparticles-modified carbon paste electrode

In the present paper, the use of a carbon paste electrode modified by 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid (3,4'AA) and ZrO2 nanoparticles prepared by a simple and rapid method was described. The heterogeneous electron transfer properties of (3,4'AA) coupled to ZrO2 nanoparticles at the carbon paste electrode were investigated using cyclic voltammetry, chronoamperometry, and square wave voltammetry in aqueous buffer solutions. Under the optimized conditions, the square wave voltammetric peak currents of hydrazine increased linearly with hydrazine concentrations in the range of 2.5 × 10(-8) to 5.0 × 10(-5) M, and detection limit of 14 nM was obtained for hydrazine. Finally, this modified electrode was used for the determination of hydrazine in water samples, using standard addition method.