Differential Pulse Voltammograms Research Articles

A Chemometric Survey about the Ability of Voltammetry to Discriminate Pharmaceutical Products from the Evolution of Signals as a Function of pH

Many pharmaceutical products are electroactive and, therefore, can be determined by voltammetry. However, most of these substances produce signals in the same region of oxidative potentials, which makes it difficult to identify them. In this work, chemometric tools are applied to extract characteristic information not only from the peak potential of differential pulse voltammograms (DPV), but also from their evolution as a function of pH. The chemometric approach is based on principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and support vector machine discriminant analysis (SVM-DA) yielding promising results for the future discrimination of pharmaceutical products in water samples.

Differential Pulse Voltammetric (DPV) Determination of Phosphomolybdenum Complexes by a Poly(Vinyl Chloride) Coated Molybdenum Blue Modified Pencil Graphite Electrode (PVC-MB-PGE)

The rapid and accurate determination of phosphate is necessary for human health and the environment. In this study, three species of inorganic phosphate were sensitively determined by the use of poly(vinyl chloride) (PVC)-coated molybdenum blue (MB) modified pencil graphite electrodes (PGEs) for the first time. The prepared electrodes were characterized by electrochemical and microscopic methods. For the determination of inorganic phosphate species, PMo12O4 3–, PMo11O39H4 7– and PMo10O38H8 11– complexes were formed by the interaction of molybdenum blue and phosphate under the optimized conditions. Peaks observed in the differential pulse voltammograms (DPVs) were due to the PO4 3–, HPO4 2– and H2PO4 – complexes and the number of molybdenum atoms in molybdenum blue. For the electrochemical determination of these complexes, each had an oxidation peak at a distinctive potential in the differential pulse voltammograms. The electrodes also showed good selectivity for the different phosphate species since they formed unique complex structure with phosphate species. The limits of detection and quantitation were determined to be 0.141 µM and 0.47 µM for PO4 3– (PMo10O38H8 11–), 0.11 µM and 0.334 µM for HPO4 2– (PMo12O40 3–), and 0.129 µM and 0.432 µM for H2PO4 – (PMo11O39H4 7–), respectively.

A Chitosan/TiO2 Nanoparticles-Entrapped Carbon Paste Electrode Covered With dsDNA as a New Electrochemical Biosensor for the Determination of Acetaminophen

A rapid, sensitive and inexpensive method was proposed for electrochemical determination of acetaminophen (ACT) using a carbon paste electrode modified with chitosan/TiO2 nanoparticles covered with double-stranded deoxyribonucleic acid (dsDNA) as working electrode. Interaction between the ACT and immobilized dsDNA accumulates ACT on the electrode surface. Differential pulse voltammogram was recorded using pulse amplitude of 0.05 V and scan rate of 25 mV/s. A peak current related to the concentration of ACT at about 550 mV was taken as an analytical signal. The effects of different experimental parameters on the oxidation current of the ACT were studied and optimized. The electrochemical signal was found to be linear in the concentration range of 0.50- $35.0~\mu \text{M}$ and 35.0- $300.0~\mu \text{M}$ with a detection limit of $0.14~\mu \text{M}$ . In addition, the values of RSD% for the determination of ACT at $20~\mu \text{M}$ and $155~\mu \text{M}$ were calculated to be 2.75% and 1.56%, respectively ( $n=5$ ). The accuracy of the proposed technique was evaluated by the determination of ACT in a 325-mg ACT tablet. The applicability of the method was successfully extended to the determination of ACT in serum and pill sample.

Electrochemical modification of electrodes with polymers derived from of hydroxybenzoic acid isomers: Optimized platforms for an alkaline phosphatase biosensor for pesticide detection

This work reports the electropolymerization of the three hydroxybenzoic acid isomers over pencil carbon graphite electrodes, and their characterization followed by further application in biosensors. Scanning electron microscopy images were obtained proving the electrodes modifications with homogeneous material and infrared spectra showed that the polymers present the unchanged carboxyl group suggesting that the polymerization begins through the phenol oxygen atom. pH and scan rate studies revealed that one electron and one proton are involved at the beginning of the polymerization in all of the isomers. A mechanism was proposed for all three structures based on these data. Alkaline phosphatase (ALP) enzyme was immobilized over the platforms through physical adsorption and covalent binding. Differential pulse voltammograms of 4-nitrophenol (4NP), the enzymatic product from the reaction between the ALP and 4-nitrophenylphosphate were recorded. The response with poly(2HB) and poly(4HB) was greater using the covalent binding than using physical adsorption technique, while poly(3HB) responses were lower than unmodified electrodes. Further studies using poly(2HB) and poly(4HB) platforms provided a low limit of detection of 20.0 μM, and 18.0 μM, respectively. The use of ALP allied with polymer platforms is an excellent choice for the determination of 4NP-generating organophosphorus pesticides, with low-cost and sensitive systems.

Simultaneous voltammetric determination of ascorbic acid, dopamine, acetaminophen and tryptophan based on hybrid trimetallic nanoparticles-capped electropretreated graphene

A novel nanocomposite sensor based on trimetallic nanoparticles of (Au/Ag/Pd)NPs uniformly capped electropretreated graphene oxide (EPGrO) was fabricated. The investigation and characterization of the (Au/Ag/Pd)NPs/EPGrO nanocomposite were studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) techniques. Cyclic voltammograms (CVs) of the nanocomposite electrode displayed obvious and sharp oxidation peaks for each ascorbic acid (AA), dopamine (DA), acetaminophen (AP) and tryptophan (TP) as compared to their responses at EPGrO and bare electrodes. An efficient electron mediating behavior of the nanocomposite electrode with large separation peak potentials for AA–DA, DA–AP, and AP–TP were estimated to be 0.16, 0.18 and 0.29 V, respectively. In addition, differential pulse voltammograms (DPVs) of the nanocompsite electrode showed simultaneous determination of AA, DA, AP and TP with linear calibration plots from 5–650 μM, 1–700 μM, 5–700 μM and 1–600 μM where their detection limits were calculated to be 0.24 ± 0.03, 0.02 ± 0.01, 0.12 ± 0.04 and 0.03 ± 0.01 μM, respectively. Finally, the practical application of the (Au/Ag/Pd)NPs/EPGrO nanocomposite electrode was successfully conducted for the analytical determination of AA, DA, AP and TP in real sample of human blood serum.

On-Site and Daily Stress-Measurement Using Gold-Linked Electrochemical Immuno Assay for IgA Determination

[Introduction]Mental stress is closely connected with our physical and mental wellness. In particular, depression may be associated with stress. Therefore, stress measurement can contribute to assess our lifestyle and increase our quality of life. However, objective stress-measurement is not established. To establish objective stress-measurement, an individual must indicate the stress level by obtaining numerous data continuously throughout the day. Therefore, the measurement method which can be suitable for this condition is needed. In this paper, we detect the secretory Immunoglobulin A (sIgA), which is the candidate of salivary stress-markers, with original electrochemical immunoassay: Gold-Linked Electrochemical Immuno Assay (GLEIA). This biosensor is based on a sandwich-type immunosensor, and adopt the electrochemical method to detect the reduction peak from Au nanoparticles linked to the secondary antibody. GLEIA is convenient and cost-effective that only requires low sample volume (10 µL). In addition, all devices that GLEIA needs are minimal such as note PC and portable potentiostat and printed electrode. Therefore, GLEIA method shows various advantages suitable for stress measurement as compared with other sIgA detection methods. In this paper, we aim to the on-site and continuous measurement of salivary IgA in our daily life, to determine the various concentration of sIgA in standard solution and artificial saliva using GLEIA.[Experimental]Primary Anti-IgA Antibody solution was dropped onto the working electrode for immobilizing the antibody by physical adsorption. After, the Au nanoparticle solution was mixed with the phosphate buffer (50 mM, pH=8.3). The anti-IgA to dissolve the 5 mM of phosphate buffer add the Au nanoparticle solution. For the preparing of secondary antibody modified Au nanoparticle, the antibody was conjugated with Au nanoparticle under the pH=8.3 condition and kept for 10 min at room temperature. Then, 10% BSA in PBS buffer and 1% PEG in PBS buffer were added in preparing Au solution. Finally, the concentration was adjusted for OD520=6.0 by centrifuge and exclude the supernatant. The Au Anti-IgA conjugate was diluted by 3 times with 50 w/v of trehalose (OD520=2) and dripping 5µL of this solution in the immunomodule. Then the immunomodule was dried in vacuum condition for 5 minutes. Dried immunomodule was stored at 4 ℃ until use. Different concentrations of the IgA antigen solution (0, 10, 60, 150, 300 ng/mL) were made by diluting in PBS. For the detection of Antibody-Antigen reaction, the IgA solutions were mixed in prepared immunomodule, After the 1 minute, and 1.4 µL of the solution was placed on immunosensor to incubate for 1 hour, after rinsing with PBS, and eliminate the PBS solution with the air gun. The direct redox reaction was performed in 2M KCl solution (20 µL) covering the entire three-electrode zone at room temperature.[Results and Discussion]We obtained the linear response to relate the concentration of sIgA (10-300 ng/mL) in D-PBS buffer with the artificial-saliva which includes salivary inorganic salt and typically glycoprotein (mucin). Figure 1 shows the differential pulse voltammogram of GLEIA with IgA in artificial saliva (a) and calibration curve (b). In addition, the calibration curve shows the linear range within 10-300 ng/mL and the correlation coefficient (R2) of the calibration curve for this relationship was 0.963. The peak current intensity is decreased from in standard solution. It may prevent the Antigen-Antibody reaction from artificial saliva which pH is nearly 8.5. Generally, the antibody shows the best affinity in pH= 6.5~8.4 condition. However, these results show that GLEIA is suitable for salivary IgA detection because the salivary pH is mainly neutral. Furthermore, we evaluate the selectivity of the immunosensor by comparing it with the reduction peak between IgA= 300ng/mL or 0 ng/mL and interference protein such as α-amylase, human serum albumin, immunoglobulin G (IgG), lysozyme and mucin. We acknowledge GLEIA shows the signal increasing within the existence of interference proteins. This may be the affinity of antibody and non-specific reaction between antibody and the proteins. More importantly, we recognize that the reduction peak is increasing with the concentration of sIgA in the existence of interference proteins. Therefore, GLEIA can be applied for stress measurement using salivary sIgA that can be used in daily life anywhere and anytime whenever necessary. In the future, we try to detect the sIgA in real saliva for on-site stress measurement using GLEIA and to integrate the various immunosensors for stress-markers in saliva.nd anytime whenever necessary. In the future, we try to detect the sIgA in real saliva for on-site stress measurement using GLEIA and to integrate the various immunosensors for stress-markers in saliva. Figure 1

Enzyme-free and label-free strategy for electrochemical oxaliplatin aptasensing by using rGO/MWCNTs loaded with AuPd nanoparticles as signal probes and electro-catalytic enhancers

An innovative label free electrochemical aptasensor was developed for the analysis of oxaliplatin (OXAL) for the first time. The DNA oligonucleotide (aptamer) was successfully fabricated, by covalently attaching the amino terminus of the functional DNA on the glassy carbon electrode (GCE) surface modified with reduced graphene oxide (rGO) and multi-walled carbon nanotubes (MWCNTs) loaded with AuPd nanoparticles (AuPd NPs@rGO/MWCNTs/GCE). The stepwise assembly process of aptasensor on AuPd NPs@rGO/MWCNTs/GCE was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The aptamer-OXAL complex formation led to inhibition the electron transfer of Fe(CN)63−/4- on the electrode interface, which was clearly observed by decreasing the peak current of the redox probe. Furthermore, we managed to quantitatively measure OXAL by adding different concentrations of OXAL, while monitoring the decrease of differential pulse voltammogram (DPV) responses of the redox probe. Under the optimized conditions, the electrochemical aptasensor exhibited a linear range of 0.1–170.0 nmol L−1 with LOD of 60.0 pmol L−1. Next, we successfully applied the aptasensor calibrated system to determine OXAL in pharmaceutical injection and human biological samples.

Electrochemical Characterization of Current‐Producing Human Oral Pathogens by Whole‐Cell Electrochemistry

AbstractExtracellular electron transfer (EET) via cell‐bound redox enzymes and/or redox shuttles is extensively studied in environmental bacteria. Meanwhile, EET capable pathogens have been identified in the human gut. However, other EET‐capable bacterial niches where possible biofilm infections are prominent have scarcely been explored. Herein, we electrochemically characterized human oral biofilm pathogens, Aggregatibacter actinomycetemcomitans and Porphyromonas gingivalis, to examine their EET capability. Both strains showed current production with the electrode poised at +0.4 V vs. a standard hydrogen electrode, which was associated with a decrease in electron‐donor concentration, coupled with the appearance of oxidative peaks in differential pulse (DP) and cyclic voltammograms (CV). Addition of antibiotics that suppress the biosynthesis of membrane or protein showed a significant current decrease, demonstrating that current production reflects the cellular activity in these pathogens. DPV‐ and CV‐based kinetic analyses supported by transmission electron microscopy of the cells stained for transition metals suggest a potential EET mechanism associated with the presence of redox enzymes on the cell membrane. These results could be the basis to reevaluate human oral pathogens from an electroactive point of view. The identified electrochemical activity of the two strains can be an effective test for assessing the impact of antibacterial compounds on the pathogen cellular activity on an electrode.

Electro-kinetics of conversion of NO3− into NO2−and sensing of nitrate ions via reduction reactions at copper immobilized platinum surface in the neutral medium

The electrocatalytic reduction of NO3− in neutral medium was investigated at Cuelectro-deposited Pt electrodes. Inherently, the fabricated Pt–Cu electrode surface contains Cu (I) and Cu (II) oxides. The presence of these oxides decreases the efficiency of the electrode pertaining to nitrate reduction reactions (NRR). Since Cu (II) reduction wave and nitrate reduction wave appear closely, this makes complicated for proper kinetic analysis using a Pt–Cu electrode. Thus, oxide deficient electrode was fabricated in–situ by applying a deposition potential at – 0.45 V for 2 min prior to voltammetric scanning for NRR. The voltammetric investigations showed that the oxide deficit (OD) Pt– Cu electrode has an enhanced catalytic effect (i.e. positive shift of the peak potential and an increased reduction current) on NRR than an oxide rich (OR) Pt–Cu electrode. A nitrate ion (NO3−) is converted into a nitrite ion (NO2−) following a step-wise mechanism, where formal reduction potential and the standard rate constant was evaluated as −0.46 V (vs. Ag/AgCl (sat.KCl) ref. electrode) and 2.48 × 10−4 cm s−1, respectively. In diagnostic exploration, Differential pulse voltammograms (DPV) were recorded over a large concentration range of NO3− between 0.12 and 4.75 mM at room temperature, which exhibited linear relationship with two linear dynamic range (LDR) having a break point at 0.99 mM. This electrode displayed an excellent sensitivity (2.3782 μAμM−1cm−2), ultra-low detection limit (LOD: 0.159 μM; S/N = 3), long term stability, very good repeatability and reproducibility.

An electrochemical sensor modified with nickel nanoparticle/nitrogen-doped carbon nanosheet nanocomposite for bisphenol A detection

Three-dimensional hierarchical cylinder-like nickel nanoparticle/nitrogen-doped carbon nanosheet/chitosan nanocomposite (NiNP/NCN/CS) is used for the modification of glassy carbon electrode (GCE) to construct an electrochemical sensor for bisphenol A (BPA) detection. The NiNP/NCN nanocomposite is synthesized by one-step pyrolysis of nickel-1,3,5-benzenetricarboxylicacid metal-organic frameworks under nitrogen atmosphere, and is demonstrated to have large specific surface area, good electrical conductivity, strong electrocatalytic activity, and high antifouling ability, which result in high sensitivity and improved reproducibility for BPA detection. In addition, the high antifouling behavior of the NiNPs/NCN/CS/GCE towards BPA is demonstrated to very likely originate from the formation of electroactive o-benzoquinone and p-benzoquinone as byproducts during the electro-oxidation of BPA. For the BPA sensor, two linear differential pulse voltammogram responses can be obtained in the concentration ranges of 0.1–2.5 μM and 2.5–15.0 μM. The detection limit for BPA detection is estimated to be 45 nM (S/N = 3). Additionally, the BPA sensor has strong anti-interference ability and good stability, and can be eventually employed to detect BPA in milk samples.

Electrochemical detection of amikacin sulphate using reduced graphene oxide and silver nanoparticles nanocomposite

This work examined the electrochemical detection of amikacin sulphate by utilizing a nano composite of green synthesized silver nanoparticles and reduced graphene oxide (AgNPs/rGO) on a nickel foam (NiF) electrode. The average size of AgNPs was 35 nm. The transmission electron microscopic and field emission scanning electron microscopic images of the rGO-AgNPs composite confirmed that the AgNPs stiffly adhered to the rGO sheets. The cyclic voltammetry (CV) and differential pulse voltammograms (DPVs) were employed for the characterization of electrodes. The electrochemical behavior of the (NiF-AgNPs/rGO) electrode and the surface confined oxidation of amikacin sulphate were confirmed by CV. The developed sensor showed a linear electrochemical response in the range of 0.05–15 μM with a detection limit of 38 nM. The developed sensor exhibited reproducibility with a relative standard deviation of 1.01% and storage stability over four weeks. The results revealed that owing to the uniform distribution of AgNPs on rGO; the fabricated sensor had high selectivity and response to amikacin sulphate detection. Moreover, the practical viability of the developed sensor was evaluated in spiked human urine samples under validated conditions. The recovery rate was in the range of 99%–102%, which indicates the sensor’s effectiveness in the detection of amikacin sulphate.

Study on the interactions between graphene quantum dots and Hg(II): Unraveling the origin of photoluminescence quenching of graphene quantum dots by Hg(II)

The present investigation reveals that when Hg(II) interacts with the colloidal solution of graphene quantum dots (GQDs), initially it forms complex with GQDs and then reduces to Hg(0) and Hg(I) resulting the complete quenching of GQDs blue luminescence. This is in contradiction with the earlier reports in which the quenching of GQDs by Hg(II) is attributed to complexation alone. In order to understand the reasons for the quenching of GQDs by Hg(II), a detailed study was undertaken by varying the pH of GQDs solution, incubation time and concentration of Hg(II). The emission studies indicate that formation of Hg(0) is less favorable at pH 7 whereas its formation is more favorable at pH 13. It is assumed that the formation of Hg(OH)2 in alkaline pH facilitates Hg(II) reduction easier than at neutral pH. The SEM and TEM images confirm the presence of spherical Hg(0) particles with different sizes depending upon Hg(II) concentration, pH and incubation time. The results obtained from emission, XPS and differential pulse voltammetry (DPV) studies reveal that Hg(II) was reduced to Hg(0) via Hg(I) on GQDs surface. The differential pulse voltammogram of 40 min incubated Hg(II)-GQDs coated GC electrode shows three oxidation peaks at 0.34, 0.48 and 0.65 V, corresponding to Hg(I) to Hg(II) and Hg(0) to Hg(II), respectively.

Distance Dependence of Electronic Coupling in Rigid, Cofacially Compressed, π-Stacked Organic Mixed-Valence Systems.

A series of new π-stacked compounds, 1,8-bis(2',5'-dimethoxybenzene-1'-yl)naphthalene (1), 1,4-bis(8'-(2″,5″-dimethoxybenzene-1″-yl)naphthalen-1'-yl)benzene (2), and 1,8-bis(4'-(8″-(2‴,5‴-dimethoxybenzene-1‴-yl)naphthalen-1″-yl)benzene-1'-yl)naphthalene (3), have been synthesized and characterized herein as precursor molecules of monocationic mixed-valence systems (MVSs). The three-dimensional geometries of these compounds were determined by X-ray crystallography. A near-orthogonal alignment of the naphthalene pillaring motif to the dimethoxybenzene redox center, or the phenylene spacer, imposes cofacial alignment of these units in a juxtaposed manner with sub-van der Waals interplanar distances. Cyclic and differential pulse voltammograms reveal that the ΔE values between two sequential oxidation potentials are 0.30, 0.11, and 0.10 V for 1, 2, and 3, respectively. MVSs derived from these compounds are recognized as class II according to the Robin and Day classification. The decay parameter β, which describes the distance dependence of the squared electronic coupling in the three mixed-valence systems, was experimentally determined via Mulliken-Hush analysis of the intervalence charge transfer band (β = 0.37 Å-1) and theoretically assessed from charge-resonance contributions derived from DFT computations (β = 0.37 Å-1). These values are extraordinarily mild, indicating that the electronic interaction between redox centers in the longitudinal direction may be comparable to that in the transverse direction, if the MVS system is appropriately designed.

Selective Voltammetric Determination of Nitrite Using Cobalt Phthalocyanine Modified on Multiwalled Carbon Nanotubes

Nitrite (NO2−) is a ubiquitous inorganic pollutant presented in the food industry and drinking water. In addition, NO2− as a toxic contaminant probably threaten human health by producing N-nitrosamines with highly carcinogenic. Voltammetric biosensing is considered the most promising approach because it offers a fast, reliable, and low-cost detection. In this article, cobalt (II) phthalocyanine (CoPc) was immobilized on multiwalled carbon nanotubes (MWCNTs), then immobilized on glassy carbon electrode (GCE) as an electrochemical senor toward nitrite using the voltammetric technique. Consequently, differential pulse voltammogram (DPV) is employed for nitrite determination, which reached a linear dynamic range of 0.01 to 1050.0 mM with a detection limit (LOD) of 2.11 μM. Such excellent performance is ascribed to the synergistic effect between CoPc and MWCNT, indicating the promise of applying CoPc/MWCNTs@GCE in the practical bio-sensing applications.

Iron complex of a quadruply fused porphyrin: Synthesis, structure and redox properties

An iron(II) complex of a quadruply ring-fused porphyrin (QFP), Fe-1, in which four mesityl groups were introduced at the periphery to improve the solubility in organic solvents, has been newly synthesized and characterized. In the pyridine solution, two pyridine molecules bind to the low-spin Fe[Formula: see text] center of Fe-1 as axial ligands to make the complex stable even under air. Characterization of Fe-1 was performed using 1H NMR spectroscopy, MALDI-TOF-MS spectrometry and single-crystal X-ray diffraction analysis. The 1H NMR signals of Fe-1 were observed in the diamagnetic region, reflecting the low-spin state of the FeII center. In the differential pulse voltammogram of Fe-1, three oxidation waves and four reduction waves were observed in pyridine; the first oxidation wave at -0.08 V vs. Fc/Fc[Formula: see text] can be ascribed to the oxidation process of the FeII center, FeII/FeIII, and other six waves can be assigned to the redox processes of the QFP ligand. Furthermore, the ESR measurement of 1e[Formula: see text]-reduced Fe-1 upon controlled-potential bulk electrolysis in pyridine exhibited a signal at [Formula: see text] = 2.003 with a well-resolved 45-line hyperfine splitting at room temperature, due to the coupling with four nitrogen nuclei and twelve hydrogen ones of the QFP ligand. This indicates that the ligand radical anion of Fe-1 is stabilized by delocalization of the spin density owing to the peripheral ring fusion and resultant expansion of the [Formula: see text]-conjugation.

An electrochemical peptide-based biosensor for the Alzheimer biomarker amyloid-β(1-42) using a microporous gold nanostructure.

Alzheimer's disease (AD) is connected to aggregation of amyloid-β (Aβ) peptide and formation of insoluble plaques in the brain. Aβ level can be monitored as an AD early diagnosis route. In this study, an irregular shaped microporous gold nanostructure with a typical size of 150 × 250nm was electrodeposited on a polycrystalline gold surface at 0mV (vs. AgCl) using sodium alendronate. The nanostructure was then characterized by field-emission scanning electron microscopy. An electrochemical peptide-based biosensor was fabricated by immobilizing an Aβ(1-42)-binding peptide on the gold nanostructure. Binding of Aβ(1-42) by the peptide was followed electrochemically using ferro/ferricyanide as a redox probe. Differential pulse voltammograms in a potential range of 0-500mV (vs. AgCl) with typical peak potentials at 224mV are linear in the 3-7000pgmL-1 Aβ(1-42) concentration range, with a 0.2pgmL-1 detection limit. The biosensor is free of interferences and was applied to the quantitation of Aβ(1-42) in artificial cerebrospinal fluid and spiked serum samples. Graphical abstractSchematic presentation of an immobilized amyloid-β(1-42)-specific peptide on the surface of a microporous gold nanostructure to fabricate an electrochemical biosensor for early diagnosis of Alzheimer's disease. Aβ(1-42) capturing by the peptide led to repulsion of ferrocyanide/ferricyanide redox couple.

Activating ZnWO4 nanorods for efficient electroanalysis of bisphenol A via the strategy of In doping induced band gap change

The design and development of an ideal method for treating and monitoring endocrine disruptors have become one of the greatest challenges for solving the problems of environment and human health. In this study, different proportions of In were doped into ZnWO4 nanorods by hydrothermal methods. The effect of the doped In element on its structure, morphology, electrocatalytic performance was systematically studied. Modified carbon paste electrode by different ratios of In-doped ZnWO4 nanorods a simple, rapid and sensitive electrochemistry sensor for bisphenol A(BPA) was developed. The results show that the catalytic efficiency of In-doped ZnWO4 nanorods for BPA was 3.6 times higher than that of pure ZnWO4. The proposed sensor produced a wide linear range of 0.01–20 μM and a low detection limit (3.4 nM, S/N = 3) by differential pulse voltammograms measurements. Satisfactory repeatability, stability and anti-interference performance are also achieved on In-doped ZnWO4/CPE. Meanwhile, the proposed sensor realizes the detection of BPA spiked in local tap water samples successfully. Moreover, the possible mechanism of In-doped ZnWO4 nanorods for BPA catalysis and the feasibility of ZnWO4 doping modification were clarified, which provides a novel and effective strategy for the design and synthesis of high performance electrocatalysts.

Fabrication of disposable electrochemical dopamine sensor using photoluminescent graphene oxide

Graphene oxide (GO) with photoluminescent property was prepared by modifiedHummer’s method. Spectroscopic and morphological studies were carried out using photoluminescence spectroscopy, UV-Vis absorption spectroscopy, FT-IR, XRD and FE-SEM. Electrochemical dopamine sensor was fabricated by drop casting GO onto screen printed carbon electrodes (SPCE). Cyclic voltammogram, differential pulse voltammogram and amperometry were performed to test the fabricated sensor. The sensor exhibits wide detection range of 12.5 μM to 1 mM dopamine concentrations in 0.1 M PBS of pH 7.4. The major interferents such as ascorbic acid shown negligible current response compared to dopamine.

Novel Fe2O3@CeO2 Coreshell‐based Electrochemical Nanosensor for the Voltammetric Determination of Norepinephrine

AbstractA new selective carbon paste electrode (CPE), was applied as an electrochemical sensor for the detection of norepinephrine (NOE). The sensor was modified with 6‐amino‐4‐(3,4‐dihydroxyphenyl)‐3‐methyl‐1,4‐dihydropyrano[2,3‐c],pyrazole‐5‐carbonitrile (ADPC) assisted Fe2O3@CeO2 coreshell nanoparticles (CNs) synthesized by simple method. To identify the redox properties of the modified electrode, and to examine its electrochemical properties, cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV) were conducted. Through electrochemical investigations, the coefficient of electron transfer between ADPC and the CNs/CPE (i. e. carbon paste electrode which was modified with CNs), the apparent charge transfer rate constant (ks), and the diffusion coefficient (D) were calculated. The NOE oxidation occurred at the optimum pH of 7.0 and a potential that was about 235 mV less positive than that of the unmodified carbon paste electrode. The interaction between the two metals in the Fe2O3@CeO2 coreshell led to an increase in the surface area and, consequently a sharp increase in the current. The differential pulse voltammogram of NOE showed two linear dynamic ranges an excellent detection limit (3σ) of 40 nM. In addition, NOE, AC and Trp were simultaneously determined at the modified electrode. Finally, NOE was quantitated in a number of real samples.

Synthesis of ZnO and CuO co-decorated porous carbon spheres with simultaneous accessibility to small biomelucules

ZnO and CuO co-decorated porous carbon spheres (PCS) were prepared via a simple hydrothermal method, denoted as ZnO-CuO/PCS. An electrochemical sensor based on the ZnO-CuO/PCS was fabricated for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Three well-resolved anodic peaks along with greatly increased peak currents were obtained at the ZnO-CuO/PCS modified glassy carbon electrode (GCE) on the differential pulse voltammograms. The anodic peak separations at the ZnO-CuO/PCS/GCE were 204 mV between AA and DA and 132 mV between DA and UA. Notably, the analytical performances of the ZnO-CuO/PCS outperform those of ZnO/PCS and CuO/PCS, which can be attributed to the synergistic effect of the two metallic oxides, i.e., the formation of p-n heterojunctions between p-type CuO and n-type ZnO allows sensitive transduction into remarkable changes in the electrochemical signals. The ZnO-CuO/PCS/GCE also presented high anti-interference ability, storage stability and repeatability in the determination of AA, DA and UA. Finally, the practical applicability of the prepared sensor was successfully demonstrated by the simultaneous determination of AA, DA and UA in human urine samples.