Number Of Cyclic Voltammetry Cycles Research Articles

Development towards a novel screening method for nipecotic acid bioisosteres using molecular imprinted polymers (MIPs) as alternative to in vitro cellular uptake assays

Impaired expression of GABA transporters (GATs) is closely related to the pathogenesis of among others Parkinson's disease and epilepsy. As such, lipophilic nipecotic acid analogs have been extensively studied as GAT1-addressing drugs and radioligands but suffer from limited brain uptake due to the zwitterionic properties of the nipecotic acid moiety. Bioisosteric replacement of the carboxylic acid group is a promising strategy to improve the brain uptake, though it requires knowledge on the binding of these isosteres to GAT1. To screen nipecotic acid isosteres for their affinity to GAT1 in a time- and cost-effective manner, this research aims to develop a molecular imprinted polymer (MIP) that mimics the natural binding site of GAT1 and can act as an alternative screening tool to the current radiometric and mass spectrometry cellular-based assays. To this end, a nipecotic acid MIP was created using the electropolymerization of ortho-phenylenediamine (oPD) by cyclic voltammetry (CV). The optimization of the generated receptor layer was achieved by varying the scan rate (50–250 mV/s) and number of CV cycles (5–12), yielding an optimized MIP with an average imprinting factor of 2.6, a linear range of 1–1000 nm, and a theoretical LOD of 0.05 nm, as analyzed by electrical impedance spectroscopy (EIS). Selectivity studies facilitated the investigation of major binding interactions between the MIP and the substrate, building an experimental model that compares characteristics of various analogs. Results from this model indicate that the substrate carboxylic acid group plays a more important role in binding than an amine group, after comparing the binding of cyclohexanecarboxylic acid (average IF of 1.7) and piperidine (average IF of 0.46). The research culminates in a discussion regarding the feasibility of the in vitro model, comparing the synthetic system against the biological performance of GAT1. Thus, evaluating if it is possible to generate a synthetic GAT1 mimic, and if so, provide directions for follow-up research.

Titanium germanium carbide MAX phase electrocatalysts for supercapacitors and alkaline water electrolysis processes

Developing electrochemically active, stable, and low-cost electrocatalysts for electrochemical devices is a significant breakthrough. Accordingly, MAX phases, emerging three-dimensional materials, are considered outstanding candidates due to their excellent electrocatalytic and electrochemical properties. Herein, the titanium germanium carbide (Ti3GeC2) MAX phase with a layered structure manufactured through reactive sintering was regarded as the electrocatalyst. In the current work, the electrocatalytic activity of the Ti3GeC2 was investigated for electrochemical devices. It was observed that adding activated carbon to the Ti3GeC2 enhances the conductivity and active area, leading to an excellent specific capacitance (349 Fg-1) for supercapacitors. Also, the capacitance of Ti3GeC2 was increased by increasing the number of cyclic voltammetry cycles. In another application, Ti3GeC2 showed substantial activity for hydrogen and oxygen evolution reactions in alkaline media. As a result, the alkaline water electrolysis system using Ti3GeC2 showed the highest current density of 10 mA cm−2 at 1.36 V and outstanding stability over 400 cycles.

Investigation of cycling effect on the enhancement of electrochemical activity of zinc doped nickel oxide

Supercapacitor activity can be greatly influenced by the doping, conductivity, and the morphology of the electrocatalyst surface. Here, we are reporting the synthesis and characterization of undoped and zinc doped nickel oxide nanoparticles for investigating the influence of doping and cyclability on the supercapacitor activity using cyclic voltammetry (CV) measurements. We found that the activity of zinc doped NiO initially increases as per increase in number of CV cycles up to the fifty cycles and beyond this it decreases further. It is interesting to note that the cyclic voltammetry changes the morphology of the electrocatalyst surface, which enhances its activity. The polarization study of the fresh and cycled electrode showed the increase of Ni +3 content for the cycled electrode is responsible for the enhanced activity. Further, the impedance and galvanostatic charge discharge analysis showed that the pseudocapacitance of the cycled zinc doped electrode is higher than that of cycled nickel oxide electrode. Phenomenologically, the presence of Ni +3 and the increased electronic conductivity due to presence of zinc, with cyclic voltammetry cycling changes the energy of the surface, which increases the supercapacitor activity.

The surface coating strategy enhances the lithium storage performance of Ni3S2@PPy self-supporting as anode materials for lithium-ion batteries

Ni3S2 materials were innovatively in-situ grown on nickel foam by the one-step reflux method. Then, a polymer PPy conductive film was successfully coated on the surface of Ni3S2 materials by electrodeposition to prepare the self-supporting Ni3S2@PPy composites on nickel foam. The content of PPy on the surface of Ni3S2 materials was controlled by changing the number of cyclic voltammetry cycles in the electrodeposition process. Ni3S2@PPy has presented the best lithium storage performance when the number of cyclic voltammetry cycles is 1. After 100 cycles (50 mA g−1), the discharge capacity remained at 396.5 mAh g−1, and the charge transfer impedance decreased with the reaction. After PPy coating on the surface of Ni3S2 material, the problem of the rapid decline of Ni3S2 electrode capacity after 50 cycles was significantly improved, and enhanced the stability of the late cycle.

A New Hybrid Sensitive PANI/SWCNT/Ferrocene-Based Layer for a Wearable CO Sensor.

Developing a sensing layer with high electroactive properties is an important aspect for proper functionality of a wearable sensor. The polymeric nanocomposite material obtained by a simple electropolymerization on gold interdigitated electrodes (IDEs) can be optimized to have suitable conductive properties to be used with direct current (DC) measurements. A new layer based on polyaniline:poly(4-styrenesulfonate) (PANI:PSS)/single-walled carbon nanotubes (SWCNT)/ferrocene (Fc) was electrosynthesized and deposed on interdigital transducers (IDT) and was characterized in detail using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), and X-ray diffraction (XRD). The sensor characteristics of the material towards carbon monoxide (CO) in the concentration range of 10–300 ppm were examined, showing a minimal relative humidity interference of only 1% and an increase of sensitivity with the increase of CO concentration. Humidity interference could be controlled by the number of CV cycles when a compact layer was formed and the addition of Fc played an important role in the decrease of humidity. The results for CO detection can be substantially improved by optimizing the number of deposition cycles and enhancing the Fc concentration. The material was developed for selective detection of CO in real environmental conditions and shows good potential for use in a wearable sensor.

Assessing Surface Coverage of Aminophenyl Bonding Sites on Diazotised Glassy Carbon Electrodes for Optimised Electrochemical Biosensor Performance.

Electrochemical biosensors using carbon-based electrodes are being widely developed for the detection of a range of different diseases. Since their sensitivity depends on the surface coverage of bioreceptor moieties, it necessarily depends on the surface coverage of amine precursors. Electrochemical techniques, using ferrocene carboxylic acid as a rapid and cheap assay, were used to assess the surface coverage of amino-phenyl groups attached to the carbon electrode. While the number of electrons transferred in the first step of diazotisation indicated a surface coverage of 8.02 ± 0.2 × l0−10 (mol/cm2), and those transferred in the second step, a reduction of nitrophenyl to amino-phenyl, indicated an amine surface coverage of 4–5 × l0−10 (mol/cm2), the number of electrons transferred during attachment of the amine coupling assay compound, ferrocene carboxylic acid, indicated a much lower available amine coverage of only 2.2 × l0−11 (mol/cm2). Furthermore, the available amine coverage was critically dependent upon the number of cyclic voltammetry cycles used in the reduction, and thus the procedures used in this step influenced the sensitivity of any subsequent sensor. Amine coupling of a carboxyl terminated anti-beta amyloid antibody specific to Aβ(1-42) peptide, a potential marker for Alzheimer’s disease, followed the same pattern of coverage as that observed with ferrocene carboxylic acid, and at optimum amine coverage, the sensitivity of the differential pulse voltammetry sensor was in the range 0–200 ng/mL with the slope of 5.07 µA/ng·mL−1 and R2 = 0.98.

Tunable Electrochemical Grafting of Diazonium for Highly Sensitive Impedimetric DNA Sensor

The development of a simple, rapid, and reliable method for detecting the virus at very low levels is therefore an important health objective. To that end, a gold surface was electrochemically modified by reducing 4-nitrobenzenediazonium tetrafluoroborate. The rate of radical formation and its polymerization were significantly affected by the reaction temperature, the concentration of the diazonium precursor solution, the number of cyclic voltammetry cycles, and the scan rate. The nitro functional group was subsequently electrochemically converted into the corresponding amine. In order to detect target DNA related to dengue virus, glutaraldehyde was used to link probe DNA to the amino functional group, after which the immobilized probe DNA was hybridized with various concentrations of target DNA. Ferri/ferrocyanide signals during each step in the overall transformation, including diazonium modification, reduction to the amine, probe DNA immobilization, and target DNA hybridization, were monitored by cyclic voltammetry and electrochemical impedance spectroscopy. We finally investigated the quantitative relationship between the change in charge-transfer resistance in response to target DNA hybridization and its concentration. This sensor responded linearly in the 100 pM to 1 nM concentration range, and its detection limit was determined to be 40.6 pM.

A nonenzymatic electrochemical glucose sensor based on molecularly imprinted polymer and its application in measuring saliva glucose

Diabetes mellitus (DM) is often diagnosed by invasive or enzymatic methods being progressively somewhat undesirable. If salivary glucose (SG) level correlates with blood glucose (BG), it could be useful for early DM detection. In this work, a molecular imprinted polymer (MIP) approach was used to develop an electrochemical non-enzymatic sensor to determine SG in micro-molar levels. The MIP based Screen printed gold electrode (Au-SPE) was prepared by electropolymerizing Acrylamide/Bis-Acrylamide (AAM/NNMBA) in the presence of glucose (G) as a template. The Cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) techniques were employed for the electrochemical measurements with Ferri/Ferrocyanide as redox probe in phosphate buffer saline. Morphological characterizations of the elaborated sensors were performed by using atomic force microscopy (AFM) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS). Important parameters influencing the MIP sensor performances such as extraction, incubation time, potential range and number of CV cycles, were studied and optimized. Under optimum conditions, the sensor could effectively detect glucose avoiding interferences of structural similar substances like lactose and sucrose. In a working range from 0.5 to 50 μg/mL, it exhibits a detection and quantification limits of 0.59 μg/mL and 1.9 μg/mL, respectively. Additionally, the real saliva glucose determination was compared to those of finger prick blood with satisfactory results (R2 = 0.99) by using partial least squares (PLS) statistical technique. Correspondingly, this work has demonstrated a cheap, simple and effective sensing platform for non-enzymatic glucose detection thus making it a promising tool for future evolution of accurate and reliable non-invasive DM diagnosis.

Electrochemical determination of enrofloxacin based on molecularly imprinted polymer via one-step electro-copolymerization of pyrrole and o-phenylenediamine

A novel molecularly imprinted polymer (MIP), poly(pyrrole-co-o-phenylenediamine) (p(Py-co-OPD)), has been developed in order to construct an enrofloxacin (EF) sensor by using cyclic voltammetry (CV) technique. The preparation conditions including the pH level, EF concentration, the number of CV cycles, extraction solution of the template and the incubation time were optimized. The performance of the MIP sensor was evaluated by square wave voltammetry (SWV). Under the optimal experimental conditions, the MIP sensor exhibited long time stability, good selectivity and a wide linear range of 1.0×10−4–1.0×10−10mol/L with a low detection limit of 6.57×10−13mol/L towards EF. Moreover, the sensor was successfully used to determine the EF amount in the pharmaceutical samples with satisfactory results.

A highly selective electrochemical sensor based on molecularly imprinted polypyrrole-modified gold electrode for the determination of glyphosate in cucumber and tap water.

An electrochemical sensor based on molecularly imprinted polypyrrole (MIPPy) was developed for selective and sensitive detection of the herbicide glyphosate (Gly) in cucumber and tap water samples. The sensor was prepared via synthesis of molecularly imprinted polymers on a gold electrode in the presence of Gly as the template molecule and pyrrole as the functional monomer by cyclic voltammetry (CV). The sensor preparation conditions including the ratio of template to functional monomers, number of CV cycles in the electropolymerization process, the method of template removal, incubation time, and pH were optimized. Under the optimal experimental conditions, the DPV peak currents of hexacyanoferrate/hexacyanoferrite changed linearly with Gly concentration in the range from 5 to 800ng mL-1, with a detection limit of 0.27ng mL-1 (S/N=3). The sensor was used to detect the concentration of Gly in cucumber and tap water samples, with recoveries ranging from 72.70 to 98.96%. The proposed sensor showed excellent selectivity, good stability and reversibility, and could detect the Gly in real samples rapidly and sensitively. Graphical abstract Schematic illustration of the experimental procedure to detect Gly using the MIPPy electrode.

Preparation of Porous Ni–Cu Alloy Electrodes and their Electrocatalytic Performance as Cathode for Hydrogen Evolution Reaction in Alkaline Solution

Porous Ni–Cu alloy electrodes were conveniently fabricated by galvanic displacement reaction (GDR) between Ni foam and copper ion in copper ion solutions, followed by cyclic voltammetry (CV) treatment to form a hierarchical microstructure. The electrocatalytic performance of prepared electrodes in terms of the hydrogen evolution reaction (HER) was investigated in a 1[Formula: see text]mol/L KOH solution at room temperature. Different copper ion solutions were tested to determine the best copper ion solution and the optimum GDR time, and experimental results show that all cathodes obtained by GDR between Ni foam and copper ion exhibit a superior HER activity over the pure Ni foam cathode, while the HER activity of electrode obtained by GDR between Ni foam and copper ion in 0.5[Formula: see text]mol/L CuCl2 solutions for 1[Formula: see text]h is the highest. Furthermore, it is found that the HER activity of electrode obtained by GDR between Ni foam and copper ion in 0.5[Formula: see text]mol/L CuCl2 solutions for 1[Formula: see text]h can be further enhanced through a CV treatment and the optimal number of CV cycles is 3, which can be attributed to a hierarchical microstructure (a needle-like nano–microstructure formed on the surface of the electrode during the CV treatment process).

Plastic antibody for the electrochemical detection of bacterial surface proteins

This work presents a novel molecularly imprinted polymer (MIP) for the indirect detection of bacteria, by targeting an outer membrane protein on a disposable device. Protein A (PA) was selected for this purpose, as a representative protein of the outer surface of Staphylococcus aureus. The imprinted polymer was assembled directly on a film of single walled carbon nanotubes (SWCNTs), placed on screen-printed electrodes (SPEs). The MIP material was produced by electropolymerizing 3-aminophenol in the presence of the protein template (PA) using cyclic voltammetry (CV). The proteins entrapped at the polymeric backbone were digested by the action of proteolytic activity of proteinase K and then washed away to create vacant sites.The performance of the corresponding imprinted and non-imprinted electrodes was evaluated by EIS and the effect of several variables, such as monomer and template concentrations, or thickness of imprinting surface, was controlled and optimized by the number of CV cycles. The detection limit of the MIP-based sensors was 0.60nM in MES buffer. High repeatability and good selectivity were observed in the presence of a model protein BSA. The sensor performance was also tested to check the effect of inorganic ions in tap water. The detection limit observed was 16.83nM, with a recovery factor of 91.1±6.6%. The sensor described in this work is a potential tool for screening PA on-site, due to the simplicity of fabrication, disposability, short response time, low cost, good sensitivity and selectivity.

Development and characterization of an electrochemical sensor for furosemide detection based on electropolymerized molecularly imprinted polymer

A novel electrochemical sensor based on a molecularly imprinted polymer, poly(o-phenylenediamine) (PoPD), has been developed for selective and sensitive detection of furosemide. The sensor was prepared by incorporating of furosemide as template molecules during the electropolymerization of o-phenylenediamine on a gold electrode. To develop the molecularly imprinted polymer (MIP), the template molecules were removed from the modified electrode's surface by washing it with 0.25molL−1 NaOH solution. The imprinted layer was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). The sensor′s preparation conditions including furosemide concentration, the number of CV cycles in the electropolymerization process, extraction solution of the template from the imprinted film, the incubation time and the pH level were optimized. The incubation of the MIP-modified electrode, with respect to furosemide concentration, resulted in a suppression of the K4[Fe(CN)6] oxidation process. Under the optimal experimental conditions, the response of the imprinted sensor was linear in the range of 1.0×10−7–7.0×10−6molL−1 of furosemide. The detection limit was obtained as 7.0×10−8molL−1 for furosemide by using this sensor. The sensor was successfully used to determine the furosemide amount in the tablet and in human urine samples with satisfactory results.

Computer-assisted sensor design and analysis of 2-aminobenzimidazole in biological model samples based on electropolymerized-molecularly imprinted polypyrrole modified pencil graphite electrode

Molecularly imprinted polymer (MIP) of 2-aminobenzimidazole (2-AB) was prepared through electropolymerization and electrodeposition of pyrrole on a pencil graphite electrode (PGE). The ability of fabricated MIP as a sensor to the analysis of 2-AB was investigated. The preparing of MIP and quantitative measurements were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV), respectively. The applied potentials of CV to preparing MIP and non-imprinted polymer (NIP) were obtained from −1.0 to 1.9V. The DPV measurements were performed in the range of 0.63–1.25V. The imprinted polymer synthesized on the PGE surface. Several important parameters like monomer concentration, number of CV cycles, pH of DPV measurements and template concentration controlling the performance of polypyrrole were investigated and optimized. The selection of monomer was performed computationally using ab initio calculations based on restricted Hartree–Fock to evaluate the template–monomer interaction energy in the prepolymerization mixture. The electrochemical synthesized MIP showed a good selectivity and sensitivity toward 2-AB. The calibration curve was demonstrated linearity over a concentration range of 1.0×10−9–3.0×10−2M with a correlation coefficient (r2) of 0.9865. The limit of detection (LOD) for 2-AB was obtained 1.0×10−10M.

A novel surface plasmon resonance enhanced total internal reflection ellipsometric application: electrochemically grafted isophthalic acid nanofilm on gold surface

The scope of this study is to modify a Surface Plasmon Resonance (SPR) sensor slide with isophthalic acid to evaluate the possible application on the detection of copper(II) ions in aqueous media by total internal reflection ellipsometry. A gold sensor surface was modified by an electrochemical diazonium reduction modification method. The modified surfaces are characterized with cyclic voltammetry (CV) and ellipsometry. Isophthalic acid monolayer modified gold slides were used for in situ detection of aqueous Cu(2+) solution with the SPR enhanced total internal reflection ellipsometry (SPRe-TIRE) technique. Layer formation, pH dependency of adsorption, sensor response of the SPRe-TIRE and isothermal kinetic parameters were examined. A high dependency on the number of CV cycles in the monolayer-multiple layer transition was observed. The suggested sensor gave a linear response over a wide range of Cu(2+) concentrations. It was also reported that adsorption on the SPRe-TIRE sensor gave Langmuir adsorption model behavior.

An aniline-based fiber coating for solid phase microextraction of polycyclic aromatic hydrocarbons from water followed by gas chromatography-mass spectrometry

A fiber coating from polyaniline (PANI) was electrochemically prepared and employed for solid phase microextraction (SPME) of some polycyclic aromatic hydrocarbons (PAHs) from water samples. The PANI film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The applicability of this coating was assessed employing a laboratory-made SPME device and gas chromatography with mass spectrometry (GC–MS) for the extraction of some PAHs from the headspace of aqueous samples. Application of wider potential range in CV led to a PANI with more stability against the temperature. The homogeneity and the porous surface structure of the film were examined by the scanning electron microscopy (SEM). The study revealed that this polymer is a suitable SPME fiber coating for extracting the selected PAHs. Important parameters influencing the extraction process were optimized and an extraction time of 40 min at 40 °C gave maximum peak area, when the aqueous sample was added with NaCl (20%, w/v). The synthesis of the PANI can be carried out conveniently and in a reproducible manner while it is rather inexpensive and stable against most of organic solvents. The film thickness of PANI can be precisely controlled by the number of CV cycles. The resulting thickness was roughly 20 μm after 20 cycles. At the optimum conditions, the relative standard deviation (RSD) for a double distilled water spiked with selected PAHs at ppb level were 8.80–16.8% ( n = 3) and detection limits for the studied compounds were between 0.1–6 pg mL −1. The performance of PANI was, also, compared with a commercial solid coated-based SPME fiber, carbowax/divinylbenzene (CW/DVB), under similar experimental conditions.

An electropolymerized aniline-based fiber coating for solid phase microextraction of phenols from water

An aniline-based polymer was electrochemically prepared and applied as a new fiber coating for solid phase microextraction (SPME) of some priority phenols from water samples. The polyaniline (PANI) film was directly electrodeposited on the platinum wire surface in sulfuric acid solution using cyclic voltammetry (CV) technique. The efficiency of new coating was investigated using a laboratory-made SPME device and gas chromatography with flame ionization detection for the extraction of some phenols from the headspace of aqueous samples. The scanning electron microscopy (SEM) images showed the homogeneity and the porous surface structure of the film. The results obtained proved the ability of this polymer as a suitable SPME fiber coating for trapping the selected phenols. Influential parameters affecting the extraction process were optimized and an extraction time of 50 min at 50 °C gave maximum efficiency, when the aqueous sample was saturated with NaCl and adjusted at pH 2. This new coating can be prepared easily in a reproducible manner and it is rather inexpensive and stable against most of organic solvents. The PANI thickness can be precisely controlled by the number of CV cycles. At the optimum conditions, the R.S.D. for a double distilled water spiked with phenol and chlorophenols at ppb level were 4.8–17% ( n = 3) and detection limits for the studied compounds were between 0.69 and 3.7 ng ml −1, except for phenol and 4-chlorophenol. The optimized method was successfully applied to some real-life water samples.