Simple Electrochemical Method Research Articles

In situ electrochemically synthesized Pt-MoO3−x nanostructure catalysts for efficient hydrogen evolution reaction

Designing and preparing highly active and stable nanostructured Pt-based catalysts with ultralow Pt loading are still challenging for electrochemical applications such as water electrolysis and fuel cells. Here we report for the first time an in situ electrochemical process to synthesize Pt-MoO3−x nanoflakes (NFs) overgrown on commercial bulk MoS2 by employing a facile and simple electrochemical method without using any expensive precious metal salts. The overgrowth of Pt-MoO3−x NFs on the bulk MoS2 surface is conducted by applying electrical energy to the bulk MoS2 and using Pt counter electrode dissolution in an acidic solution. In spite of their 10 times lower Pt loadings compared to commercial Pt black (Alfa Aesar), the synthesized Pt-MoO3−x NFs demonstrate excellent catalytic performance with a Pt mass activity of 2.83 A/mgPt at the overpotential of 100 mV for electrochemical hydrogen evolution reaction (HER), an approximately 4 times higher value than the value of 0.76 A/mgPt at the overpotential of 100 mV for commercial Pt black. We hypothesize that the outstanding HER characteristics of Pt-MoO3−x NFs are related to the existence and increase of Pt-MoO3 interfacial sites and oxygen vacancy sites such as Mo5+ in the Pt-MoO3−x NF structures. In addition, our density functional theory (DFT) calculations demonstrate that Pt and O sites at Pt and MoO3 interfaces and O sites at defective MoO3−x in the Pt-MoO3−x NFs contribute to accelerate the HER.

Highly sensitive biosensor for detection of DNA nucleobases: Enhanced electrochemical sensing based on polyaniline/single-layer MoS2 nanosheets nanocomposite modified carbon paste electrode

Robust detection of DNA as a molecule that encodes genetic instructions is getting significant attention in recent years due to its promising applications in diseases diagnosis and treatment, forensic analysis, food safety evaluation, environmental monitoring, and so on. In this research, a simple, rapid and multiplex electrochemical method based on single-layer molybdenum disulfide (MoS2) nanosheets sensing platform and differential pulse voltammetry (DPV) method for detection of DNA nucleobases (DNANBs) was set up without any pretreatment or separation process. Hence, the carbon paste electrode modified with MoS2 (MoS2/CPE) was selected, and the effects of different parameters such as supporting electrolyte composition and pH were optimized to obtain the best peak potential separation and high sensitivity. Then, the individual, respective and simultaneous determinations of DNANBs were performed by controlling the certain experimental conditions. The results exhibited the excellent sensitivity, low limit of detection, and high selectivity of the electrochemical biosensor. Moreover, the peak current values were linearly dependent on the concentration of DNANBs. For comparison, common methods for determination of DNANBs were analyzed based on the absorption of ultraviolet light and Raman spectroscopy. Finally, the proposed electrode was modified with polyaniline (PANI-MoS2/CPE) as a new biosensor for the determination of DNANBs, exhibiting good reproducibility and stability.

Graphene–Gold Nanostructures Hybrid Composites Screen-Printed Electrode for the Sensitive Electrochemical Detection of Vancomycin

The most important and well-known glycopeptide antibiotic, vancomycin (VAN), is used for the treatment of severe bacterial infections like methicillin-resistant staphylococcal infections and endocarditis caused by enterococci and sepsis. Taking into account the problem of the development of antibiotic resistance as well as its toxicity, both correlated with the VAN concentration (CVAN) in biological samples, there is need for better and more accessible quantification methods for this antibiotic. Considering all of the above, herein, we present a simple electrochemical method for VAN sensing based on a hybrid graphene-gold nanostructure nanocomposite electrode, which allows double detection directly in the oxidation domain and also indirectly, in reduction, using the electro-active gold nanostructures as a probe to monitor the current changing due to the interaction between gold and VAN. The developed method was able to successfully detect VAN in the linear range of 1–100 µM with a limit of detection (LOD) of 0.29 µM for the direct approach and 0.5 µM for the indirect one. The selectivity of the method was tested in the presence of other antibiotics and drugs. This method was successfully applied for the detection of VAN from human serum samples.

Development of an Electrochemical Methodology for the Quantification of β-estradiol in Pharmaceutical Formulation

This paper describes a simple, inexpensive, highly sensitive, and efficient electrochemical method to determine Estradiol in pharmaceutical formulations. The oxidation reaction on the electrode surface was electrochemically characterized by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of Estradiol at carbon paste electrode revealed a non-reversible oxidation peak at +640 mV vs. Ag/AgCl, which was used for electrochemical detection of Estradiol. The operating parameters (pH, frequency, step potential, and amplitude) were optimized in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 0.059 - 2.997 mg L -1 , with a detection limit of 21.85 µg L -1 . After calibration curve was plotted, the developed procedure was applied to determine Estradiol in parmacheutical formulation. These results show that the proposed method can be used for Estradiol quantification in pharmaceutical formulations with high sensitivity, specificity, stability, and reproducibility, and can be applied in analytical routines in laboratories of quality control analysis in drugs. DOI: http://dx.doi.org/10.17807/orbital.v11i4.1332

Electrochemical detection of circRNAs based on the combination of back-splice junction and duplex-specific nuclease

Covalently closed circular RNA (circRNA) has potential implications for disease diagnosis and therapy. However, current methods for circRNA detection are infrequent, and require RNase R pretreatment in general, which is deviation-oriented and labor-intensive. Herein, we have developed a simple electrochemical method for direct detection of circRNA. Firstly, the hairpin probes are designed to identify circRNA based on back-splice junction (BSJ) sites. Then, the selection of substrate length by duplex-specific nuclease (DSN) is utilized to trigger DSN-assisted amplification, resulting in significantly amplified signal. Therefore, the limit of detection of the proposed method for circRNA can reach as low as 3.47 fM, which may contribute to a better selectivity, reproducibility, and stability. This method has also been employed to assay circRNA in human serum samples, which may hold great potential in the clinical diagnosis applications.

A Sensitive Voltammetric Biosensor forEscherichia ColiDetection Using an Electroactive Substrate for $\beta$ -D-Glucuronidase

In this paper, we developed a sensitive and simple electrochemical method for the rapid detection of Escherichia coli in water samples. The general principle of the assay utilizes the enzyme $\beta $ -D-glucuronidase. This enzyme was induced by adding methyl- $\beta $ -D-glucuronide sodium salt and its activity promoted the cleavage of 8-hydroxyquinoline glucuronide to the electroactive compound 8-hydroxyquinoline. This cleavage product was further oxidized on the working electrode of a potentiostat using cyclic voltammetry. The obtained current output signal in a specific voltage range (400 to 600 mV) indicated enzyme activity and subsequently was an evidence for E. coli cells in the sample. For our experiment, we designed a low-cost potentiostat and show an evaluation of this instrument. First, the $\beta $ -D-glucuronidase assay was tested with various concentrations of enzyme solutions before living E. coli cells were investigated. Our presented method allowed a clear and a sensitive identification of 1 colony-forming unit of E. coli without any interference from other investigated bacterial strains. Comprising only few working steps (filtration, incubation, and voltammetric analysis), the method allowed incorporation into an automated prototype that delivered results similar to those obtained from samples treated in laboratory.

In situ growth of copper/reduced graphene oxide on graphite surfaces for the electrocatalytic reduction of nitrate

A fast and simple electrochemical method was developed to make composite electrodes containing monodispersed copper nanoparticles (Cu NPs) and reduced graphene oxide (rGO) for nitrate removal. The Cu/rGO/graphite plate (GP) electrodes were fabricated after in situ electrochemical exfoliation and a one-step simultaneous graphene oxide (GO) reduction and Cu deposition. Bulk electrolysis results showed the percentage of nitrate removal up to 96.8% after 3 h and the reaction rate constant of the Cu/rGO/GP electrode was 14.08, 8.00 and 1.94 times higher than those of GP, GO/GP and Cu/GP electrodes, respectively. Further analysis revealed improvements in electron transfer, adsorption of the electroactive species and electrochemically active surface area, which all contributed to the enhancement of electrocatalytic nitrate reduction. Furthermore, the mechanism of nitrate reduction with the Cu/rGO/GP electrode was studied in detail by cyclic voltammetry. The voltammogram profile of the Cu/rGO/GP electrode after 50 scanning cycles was similar to that of the initial cycle, and the percentage of nitrate removal was still at 92.4% after the eighth application, demonstrating the high stability of the composite electrode. Taking together, results showed the promising application of graphene-based electrodes with copper nanoparticles in electrocatalytic denitrification.

Electrochemical Oxidative Determination and Electrochemical Behavior of 4‐Nitrophenol Based on an Au Electrode Modified with Electro‐polymerized 3,5‐Diamino‐1,2,4‐triazole Film

AbstractA simple and fast electrochemical method was described and evaluated to determine the hazardous compound, 4‐nitrophenol (4NP). In this work, concentration of 4NP was determined by differential wave voltammetry (DPV). A gold electrode (Au) was modified with 3,5‐diamino‐1,2,4‐triazole (35DT). The modified electrode (35DT‐Au) was characterized by using electrochemical impedance spectroscopy (EIS), fouirer transform infrared spektrofotometre (FTIR), cyclic voltammetry (CV) and DPV. The modified electrode showed more sensitivity towards 4NP compared to unmodified one. A wide linear concentration range from 0.24 to 130.6 μM was obtained for 4NP with a detection limit of 0.09 μM. In the reproducibility and repeatability studies, the relative standard deviation (RSD%) values of the method were obtained as 3.72 % and 2.56 %, respectively, which are acceptable values. This proposed method was successfully used for the analysis of 4NP in lake and tap water samples. Simplicity, sensitivity, selectivity and high efficiency of the proposed method can be used in routine analysis of trace amounts of 4NP in polluted waters.

Synthesis of carbon nanofibers/poly(para-phenylenediamine)/nickel particles nanocomposite for enhanced methanol electrooxidation

Several studies have been conducted on direct methanol fuel cells (DMFCs) to resolve major issues such as the high cost of the catalyst and the poisoning of the electrode. Herein, a low-cost catalyst based on nickel particles (NiPs), carbon nanofibers (CNF) and poly(para-phenylenediamine) (PpPD) was carried out using a simple electrochemical method. The morphology and structure of the nanocomposite electrodes are characterized by field-emission gun scanning electron microscopy coupled with an energy dispersive X-ray detector, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. The effects of various parameters such as the PpPD film thickness and the NiPs content on the electrocatalytic performance of CPE/CNF/PpPD/NiPs are evaluated which lead to the optimized composition. The results of the methanol electrooxidation reaction at room temperature showed that the optimized CPE/CNF/PpPD/NiPs nanocomposite exhibits a high catalytic activity (Ip = 38.11 mA cm−2), good stability and durability for more than 6 h in comparison with CPE/CNF/NiPs. These findings truly highlight the synergetic effect of CNF/PpPD in enhancing the electrochemical activity and stability and the vast potential of CPE/CNF/PpPD/NiPs as low-cost catalyst and electrodes for DMFCs.

Charge Transfer Platform and Catalytic Amplification of Phenanthroimidazole Derivative: A New Strategy for DNA Bases Recognition.

Research about DNA composition has been concentrated on DNA damage in the past few decades. However, it still remains a great challenge to construct a rapid, facile, and accurate approach for simultaneously monitoring four DNA bases, guanine (G), adenine (A), thymine (T), and cytosine (C). Herein, a novel electrochemical sensor based on phenanthroimidazole derivative, 2-(4-bromophenyl)-1-phenyl-1H-phenanthro[9,10-d]-imidazole (PPI), is successfully fabricated by a simple electrochemical method. The bromophenyl group in PI could expand their aromatic plane, induce the π-conjugated extension, and enhance the charge transfer and π-π interaction. The phenyl group at N1 position could regulate the intermolecular interaction, which could promote the possibility of intermolecular connection. The PPI polymer (poly(PPI)) with π-electron enriched conjugation architecture has been applied in simultaneous determination of G, A, T, and C in neutral solution by square wave voltammetry (SWV) method with well-separated peak potentials at 0.714, 1.004, 1.177, and 1.353 V, respectively. The sensor functionalized with poly(PPI) exhibits wide linear response for G, A, T, and C in the concentration ranges of 3-300, 1-300, 30-800, and 20-750 μM, respectively. With favorable selectivity, stability, and reproducibility, the sensor is successfully utilized to monitor four DNA bases in real samples, displaying a promising prospect for electrochemical sensing devices.

Graphene Paper with Sharp‐edged Nanorods of Fe−CuMOF as an Excellent Electrode for the Simultaneous Detection of Catechol and Resorcinol

AbstractA flexible composite paper Fe−Cu‐based metal‐organic framework (MOF)/reduced graphene oxide (rGO) (Fe−CuMOF/rGO) electrode was prepared by using a simple electrochemical method for the simultaneous detection of catechol (CC) and resorcinol (RC). Free‐standing, flexible and double‐sided Fe−CuMOF/rGO composite paper was obtained by applying the electrochemical deposition process on the rGO paper electrode in the solution containing Fe−CuMOF composite. The morphological analysis of Fe−CuMOF/rGO composite paper showed that sea urchin‐like structures formed on the rGO electrode surface consist of numerous sharp‐edged nanorods of Fe−CuMOF. Flexible Fe−CuMOF/rGO paper electrode exhibited high sensitivity, wide linear range and low detection limit for the simultaneous determination of CC and RC. The linear ranges of concentration for CC and RC were 0.1–800 and 0.1–720 μM, respectively, and the corresponding limits of detection (S/N=3) were 0.016 and 0.020 μM. The outstanding performance of this flexible electrode could be attributed to the sharp‐edged urchin‐like Fe−CuMOF structures which provide an increment of the surface area and the electrochemical activity of the composite paper electrode. Stability tests showed that Fe−CuMOF/rGO composite paper electrode has excellent flexibility, high durability, and good reproducibility. Furthermore, this electrode exhibited high sensitivity and selectivity for the determination of CC and RC in real sample analysis.

A new simple electrochemical method for the determination of Bisphenol A using bentonite as modifier.

A simple, inexpensive, highly sensitive, selective, and novel electrochemical method was developed for determination of the Bisphenol A in samples of tap water, blood serum, and urine using a bentonite-modified carbon paste electrode. The graphite, bentonite and the working electrodes (without and chemically modified) were characterized by scanning electron microscopy, infrared absorption spectroscopy, and X-ray diffraction. The electrodes were electrochemically characterized using cyclic voltammetry, square wave voltammetry, and electrochemical impedance spectroscopy. The studied electrochemical variables were: electrode area, standard heterogeneous rate constant, charge transfer coefficient and double-layer capacitance. The bentonite as a sensor modifier had a strong influence on these variables. For the development of the methodology to quantify Bisphenol A, the instrumental parameters (frequency, amplitude, and step potential) and experimental parameters (pH, bentonite quantity) were optimized. The analytical curve to Bisphenol showed a linear response of the oxidation peak current intensity vs. the concentration in the range of 6.8 × 10-10 to 1.5 × 10-8 mol mL-1, with a limit of detection (LOD) of 2.11 × 10-11 mol mL-1 and limit of quantification (LOQ) of 7.04 × 10-11 mol mL-1. Recovery experiments were performed by adding known amounts of Bisphenol A in tap water, blood serum, and urine samples. Recovery rates using the standard addition method were in the range of 97.8-101.8%. The results demonstrated the method feasibility for quantifying Bisphenol A in these samples.

Facile Protocol for Alkaline Electrolyte Purification and Its Influence on a Ni–Co Oxide Catalyst for the Oxygen Evolution Reaction

We report a simple and effective electrochemical method to remove Fe impurities from commercial KOH electrolyte. We therefore utilize a MoS2 catalyst deposited on porous Ni foam as both the anode a...

Morphology dependent field emission from copper sulfide nanosheet arrays tailored with electrolyte concentrations in anodic oxidation process

Vertically oriented copper sulfide nanosheet arrays were successfully fabricated by a simple and manageable electrochemical anodization method at room temperature. By controlling and adjusting the concentrations of sodium sulfide electrolyte to be 0.1 M, 0.5 M, 1.0 M and 1.5 M, respectively, the morphologies of copper sulfide nanosheets (average size, thickness or density of sharp edges) could be well tailored and be more optimized for applications in field emission (FE). As the results showed, for optimal nanostructure of such copper sulfides nanosheet arrays, its turn-on field could be lowered to 2.0 V/μm and the field emission current density would reach up to 4.1 mA/cm2 under an applied field of 6.4 V/μm, and also it can exhibit excellent field emission stability, with a degradation lower than ±4% and a huge field enhancement factor of 8327.

Simultaneous, ultrasensitive detection of hydroquinone, paracetamol and estradiol for quality control of tap water with a simple electrochemical method

Real-time monitoring of possible contamination in the water supply network requires the deployment of large numbers of sensors for varied analytes, which would be economically viable only if simple methods and low-cost sensing units are available. In this paper, we demonstrate that carbon screen-printed electrodes (SPEs) can be used to determine simultaneously the presence of emerging pollutants (EP) hydroquinone (HQ), paracetamol (PARA) and estradiol (E2) in tap water, with detection limits of 185, 218 and 888 nmol L−1, respectively, within a linear range between 0.5 and 10.0 μmol L−1. This performance is competitive with high-performance liquid chromatography (HPLC), the gold-standard methodology for water analysis, being superior to any carbon-based electrochemical sensors in the literature. It was achieved with differential pulse voltammetry (DPV) using carbon SPEs pretreated through a simple procedure with cyclic voltammetry (CV) in 0.5 mol L−1 sulfuric acid solution. Pretreatment did not affect the electrode morphology but removed non-conducting residues from the printing ink, according to energy-dispersive X-ray (EDX) spectra obtained in scanning electron microscopy (SEM). Therefore, electrode conductivity increased as demonstrated in electrochemical impedance spectroscopy measurements. The pretreated SPEs were stable for at least 30 days and detection of the analytes was not affected by common interferents. Because the sensor fabrication and detection methods are simple, with potentially low-cost water analysis, the results presented here may inspire the design of sensor networks for monitoring water quality in the supply system and in the environment.

Continuous preparation of high performance flexible asymmetric supercapacitor with a very fast, low-cost, simple and scalable electrochemical co-deposition method

High performance flexible asymmetric supercapacitors based on carbon cloth are continuously prepared by a quick, low-cost, simple and scalable one-step electrochemical process within minutes without any other additives. The Fe2O3 is electrochemically deposition carbon cloth for the negative electrode, while the PEDOT and MnO2 are electrochemically co-deposited on carbon cloth for positive electrode. All processes take place within 1 min, therefore, this method can be applied in a continuous preparation mode for large-scale production, which implies its application potential in the industry. This is the first report of one-step continuous prepare of the flexible electrodes for supercapacitor. In addition, as assembled supercapacitors consisting of Fe2O3@carbon cloth and MnO2-PEDOT@carbon cloth, it achieves a high operating voltage of 2 V and a high energy density of 340 μW h cm−3 at a power density of 1.212 × 105 μW cm−3. This supercapacitor also possesses excellent flexibility and stability with 95% capacitance retained even after 1000 times bending. The larger-sized supercapacitor is further tested as watchband to power an electronic watch or light 41 LEDs for minutes. The low-cost continuous preparation method with high performance endows the flexible carbon cloth various promising applications, such as flexible asymmetric supercapacitors, flexible battery, catalysts and surface treatment.

Facile development of highly sensitive femtomolar electrochemical DNA biosensor using gold nanoneedle-modified electrode

In this paper, a simple one-step electrochemical method was employed for the deposition of gold nanostructures. Different morphologies (Au-nanorods and Au-nanoneedles) were obtained using different concentrations of gold chloride (HAuCl4·3H2O) solution. The gold nanostructure-modified surface was used for the fabrication of DNA biosensor, which was characterized by cyclic voltammetry and differential pulse voltammetry. The DNA immobilization and hybridization on Au-nanorods and Au-nanoneedles showed a detection limit of 10 fM and 0.2 fM, respectively, with wide dynamic range of 0.2 fM to 10 nM. The Au-nanoneedle electrode showed improved detection limit, which is fifty times lower than that of the Au-nanorods. The electrochemical DNA biosensor showed a good selectivity and sensitivity towards the detection of target DNA. The enhancement in response of DNA biosensor would be an exciting addition in clinical diagnosis due to an improved detection limit.

Green Synthesis of Spherical Shaped Silver Nanoparticles Using <i>Allium cepa</i> Leaves Extract and its Photocatalytic Activity

Spherical silver nanoparticles (AgNPs) (5–15 nm) were synthesized by a simple electrochemical method at room temperature using Allium Cepa (AC) leaves extract. AC leaves extract that acts as a reducing and stabilizing agent is capable of producing AgNPs without any agglomeration. The phytochemical properties of the leaves extract including total phenolic content, total flavonoid content, and its active species were studied. The crystallinity, morphology, and functional characteristics of the AgNPs were analyzed using an X–ray diffractometer, a transmission electron microscope, and a Fourier–transform infrared spectrometer, respectively. The characterization results verified the contribution of phenolic acids and flavonoids in reduction of Ag+ to metallic AgNPs and also in stabilization of the AgNPs. The catalytic activity of the AgNPs was tested towards the photodegradation of 2, 4–dichlorophenoxyacetic acid (2,4–D) herbicide, in which showing a remarkable degradation performance of 80%. The results provide strong evidence to support the potential use of AC leaves extract to act as green reducing and stabilizing agents as well as a green electrolyte to synthesize well–scattered spherical shaped AgNPs.

Dendritic silver hierarchical structures for anode materials in Li ion batteries

Dendritic silver hierarchical structures were prepared via a simple electrochemical deposition method in the presence of citric acid. The influence of the molar ratio of citric acid and AgNO3, the deposition time and the deposition current on the crystalline and morphology of the products were studied by X-ray diffraction and scanning electron microscopy. Dendritic silver hierarchical structures consist of a long trunk with secondary branches, which grew in a parallel direction with a definite angle to the trunk. The average diameter of the trunk is 230–320 nm, that of the secondary branches is about 250 nm and the length of the branches is about 850 nm. The charge specific capacity of dendritic silver hierarchical structures was stable at around 250 mAh g−1 after 500 cycles at 0.1C. They also exhibited excellent rate capability at the various current rates from 0.1 to 5C.

Minimally Invasive Glucose Monitoring Using a Highly Porous Gold Microneedles-Based Biosensor: Characterization and Application in Artificial Interstitial Fluid

In this paper, we present the first highly porous gold (h-PG) microneedles-based second-generation biosensor for minimally invasive monitoring of glucose in artificial interstitial fluid (ISF). A highly porous microneedles-based electrode was prepared by a simple electrochemical self-templating method that involves two steps, gold electrodeposition and hydrogen bubbling at the electrode, which were realized by applying a potential of −2 V versus a saturated calomel electrode (SCE). The highly porous gold surface of the microneedles was modified by immobilization of 6-(ferrocenyl)hexanethiol (FcSH) as a redox mediator and subsequently by immobilization of a flavin adenine dinucleotide glucose dehydrogenase (FAD-GDH) enzyme using a drop-casting method. The microneedles-based FcSH/FAD-GDH biosensor allows for the detection of glucose in artificial interstitial fluid with an extended linear range (0.1–10 mM), high sensitivity (50.86 µA cm−2 mM−1), stability (20% signal loss after 30 days), selectivity (only ascorbic acid showed a response about 10% of glucose signal), and a short response time (3 s). These properties were favourably compared to other microneedles-based glucose biosensors reported in the literature. Finally, the microneedle-arrays-based second-generation biosensor for glucose detection was tested in artificial interstitial fluid opportunely spiked with different concentrations of glucose (simulating healthy physiological conditions while fasting and after lunch) and by placing the electrode into a simulated chitosan/agarose hydrogel skin model embedded in the artificial ISF (continuous glucose monitoring). The obtained current signals had a lag-time of about 2 min compared to the experiments in solution, but they fit perfectly into the linearity range of the biosensor (0.1–10 mM). These promising results show that the proposed h-PG microneedles-based sensor could be used as a wearable, disposable, user-friendly, and automated diagnostic tool for diabetes patients.