An electrochemical DNA biosensor developed on novel multinuclear nickel(II) salicylaldimine metallodendrimer platform

An electrochemical DNA biosensor (EDB) was prepared using an oligonucleotide of 21 bases with sequence NH₂-5′-GAGGAGTTGGGGGAGCACATT-3′ (probe DNA) immobilized on a novel multinuclear nickel(II) salicylaldimine metallodendrimer on glassy carbon electrode (GCE). The metallodendrimer was synthesized from amino functionalized polypropylene imine dendrimer, DAB-(NH₂)₈. The EDB was prepared by depositing probe DNA on a dendrimer-modified GCE surface and left to immobilize for 1 h. Voltammetric and electrochemical impedance spectroscopic (EIS) studies were carried out to characterize the novel metallodendrimer, the EDB and its hybridization response in PBS using [Fe(CN)₆]^3−/4− as a redox probe at pH 7.2. The metallodendrimer was electroactive in PBS with two reversible redox couples at E°′ = +200 mV and E°′ = +434 mV; catalytic by reducing the E_pa of [Fe(CN)₆]^3−/4− by 22 mV; conducting and has diffusion coefficient of 8.597 × 10⁻⁸ cm² s⁻¹. From the EIS circuit fitting results, the EDB responded to 5 nM target DNA by exhibiting a decrease in charge transfer resistance (R_ct) in PBS and increase in R_ct in [Fe(CN)₆]^3−/4− redox probe; while in voltammetry, increase in peak anodic current was observed in PBS after hybridization, thus giving the EDB a dual probe advantage.     

A novel electrochemical DNA biosensor based on graphene and polyaniline nanowires

A novel DNA biosensor based on oxidized graphene and polyaniline nanowires (PANIws) modified glassy carbon electrode was developed. The resulting graphene/PANIw layers exhibited good DPV current response for the complementary DNA sequences. The good electron transfer activity might be attributed to the effect of graphene and PANIw. Graphene and PANIw nanolayers film with highly conductive and biocompatible nanostructure were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immobilization of the probe DNA on the surface of electrode was largely improved due to the unique synergetic effect of graphene and PANIw. Under optimum conditions, the biosensor exhibited a fast amperometric response, high sensitivity and good storage stability for monitoring DNA. The current response of the sensor increases linearly with the concentration of target from 2.12 × 10⁻⁶ to 2.12 × 10⁻¹² mol l⁻¹ with a relative coefficient of 0.9938. The detection limit (3σ) is 3.25 × 10⁻¹³ mol l⁻¹. The results indicate that this modified electrode has potential application in sensitive and selective DNA detection.     

Electrochemical and spectroscopic evidences of corrosion inhibition of bronze by a triazole derivative

The electrochemical behavior of the bronze (Cu-8Sn in wt%) was investigated in 3% NaCl aqueous solution, in presence and in absence of a corrosion inhibitor, the 3-phenyl-1,2,4-triazole-5-thione (PTS). The inhibiting effect of the PTS was evidenced for concentrations higher than 1 mM for the cathodic process whereas its effect was clearly seen with a concentration as low as 0.1 mM for the anodic process. A significant positive shift of the corrosion potential was also observed, and its inhibiting effect increased with both its concentration and the immersion time of the sample. From voltammetry and electrochemical impedance spectroscopy experiments, the inhibiting efficiency of the PTS was found to be in the 94-99% range for 1 mM concentration. Scanning electron microscopy and X-ray energy dispersion analysis of the specimen surface show the presence of sulphur on the surface. Raman micro-spectrometry study confirms the protective effect of the PTS in aqueous solution through three types of interactions with the electrode, namely the adsorption of the inhibitor in a flat configuration, the formation of copper-thiol molecules, and when copper is released, the formation of a polymeric complex.     

Nucleic acid biosensor for DNA hybridization detection using rutin-Cu as an electrochemical indicator

The complex of rutin-Cu (C₈₁H₈₆Cu₂O₄₈, abbreviated by Cu₂R₃, R = rutin) was synthesized and characterized by elemental analysis and IR spectra. Cyclic voltammetry (CV) and fluorescence spectroscopy were used to investigate the interaction of Cu₂R₃ with salmon sperm DNA. It was revealed that Cu₂R₃ could interact with double-stranded DNA (dsDNA) by a major intercalation role. Using Cu₂R₃ as a novel electroactive indicator, an electrochemical DNA biosensor for the detection of specific DNA fragment was developed and its selectivity for the recognition with different target DNA was assessed by differential pulse voltammetry (DPV). The target DNA related to coliform virus gene could be quantified ranged from 1.62 × 10⁻⁸ mol L⁻¹ to 8.10 × 10⁻⁷ mol L⁻¹ with a good linearity (r = 0.9989) and a detection limit of 2.3 × 10⁻⁹ mol L⁻¹ (3σ, n = 7) was achieved by the constructed electrochemical DNA biosensor.     

Electrochemical impedance studies of chitosan-modified electrodes for application in electrochemical sensors and biosensors

Graphite-epoxy resin composite (GrEC) electrodes were modified with chitosan (Chit) films and characterised using electrochemical impedance spectroscopy (EIS). Several film modifications were made using different crosslinking agents: glutaraldehyde (GA), glyoxal (GO), epichlorohydrin (ECH) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) together with N-hydroxysuccinimide (NHS) and the characteristics of each of them evaluated in the presence of model electroactive compounds potassium hexacyanoferrate(III) and hexaammineruthenium(III) chloride. Immobilisation of functionalised carbon nanotubes into chitosan matrices (Chit-CNT) using the same crosslinking agents was also investigated. The impedance of the electrode with the best performance (GrEC/Chit-CNT/EDC-NHS) was characterised as a sensor for dipyrone and hydroquinone and for a glucose biosensor by immobilisation of glucose oxidase (GOx) on top of Chit-CNT using GA. Modelling and equivalent circuit analysis was carried out, with emphasis on diffusion characteristics and the significant features of the spectra are discussed.     

Electrochemical impedance spectroscopic investigation of the role of alkaline pre-treatment in corrosion resistance of a silane coating on magnesium alloy, ZE41

The protective performance of the coatings of bis-1,2-(triethoxysilyl) ethane (BTSE) on ZE41 magnesium alloy with different surface pre-treatments were evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 0.1 M sodium chloride solution. Electrical equivalent circuits were developed based upon hypothetical corrosion mechanisms and simulated to correspond to the experimental data. The morphology and cross section of the alloy subjected to different pre-treatments and coatings were characterized using scanning electron microscope. A specific alkaline pre-treatment of the substrate prior to the coating has been found to improve the corrosion resistance of the alloy.     

Electrochemical properties of Cu2O/Cu composite particles prepared by a novel and facile method

Cu₂O/Cu composite particles were synthesized by a novel and facile chemical reduction method without any template or surfactant. X-ray diffraction (XRD) results showed that the product mainly consisted of the Cu₂O phase coexisting with a few Cu phases. Typical FE-SEM images indicated that the particles with an octahedral shape were Cu₂O. In addition, the electrochemical performance of the Cu₂O/Cu particles as the working electrode material in alkaline solution was systematically investigated. The particles showed a maximum discharge capacity of 222.9 mAh g⁻¹ at a discharge current density of 60 mA g⁻¹ and a high value of 109.1 mAh g⁻¹ after 50 charge–discharge cycles. The results of cyclic voltammetry demonstrated that the reaction between Cu₂O and Cu is the major electrochemical reaction during the charging and discharging process. The results of electrochemical impedance spectroscopy indicated that the formation of Cu₂O on the surface of Cu particles significantly increased the contact resistance and the charge transfer resistance of the electrode during the discharging process.     

Electrochemical impedance spectroscopic study of the intercalation of lithium and sodium ions into polyparaphenylene in carbonate-based electrolytes

Electrochemical impedance spectroscopy is used to investigate the electrochemical intercalation of lithium and sodium ions into polyparaphenylene under galvanostatic conditions in carbonate-based electrolyte. The evolution of the charge transfer resistance was studied at various selected potentials both during the reduction and the oxidation processes in order to control the stoichiometry of the intercalated compounds. The reversibility of the intercalation process, the effect of the cycling and the stability of the intercalated materials in the electrolyte as a function of the time were examined. A significant decrease of the charge transfer resistance occurs during the intercalation. That is related to an increase of the conductive state especially for the richest compounds Na_0.46(C₆H₄) and Li_0.50(C₆H₄).     

Anodic polymerization of 2,5-di-(2-thienyl)-furan in ethanol

Poly(2,5-di-(2-thienyl)-furan) (PSOS) was synthesized via anodic polymerization of 2,5-di-(2-thienyl)-furan (SOS) in ethanol solution containing 0.2 M LiClO₄ as supporting electrolyte. The electrochemical and spectroelectrochemical properties were investigated using electroanalytical and UV–vis spectroscopic techniques, respectively. The band gap of the polymer film was found as 2.22 eV and the film was successfully switched between black oxidized state and orange neutral state. Fluorescence and electrochemical impedance spectroscopy (EIS) studies were also performed.     

Electrochemical synthesis,characterization and capacitive properties of novel thiophene based conjugated polymer

In this paper, a novel thiophene based monomer, 1-(pyren-1-yl)-2,5-di(thiophen-2-yl)-1H-pyrrole, PThP, was synthesized and characterized by ¹H NMR and ¹³C NMR spectroscopic methods. The electrochemical behavior and electropolymerization of this novel monomer were performed on pencil graphite electrode (PGE) by cyclic voltammetry. The effect of solvent, dopant, scan number and scan rate on the electropolymerization and properties of the conjugated polymer films were investigated. The capacitive properties of the poly(PThP) films were tested by electrochemical impedance spectroscopy (EIS). The highest specific capacitance value was calculated for the conjugated polymer modified PGE that was obtained in 0.1 M tetrabutylammonium perchlorate/dichloromethane solution for 30 cycles at 25 mV/s scan rate as 25.45 mF cm⁻². The surface morphologies of the conjugated polymer modified electrodes were determined by scanning electron microscopy (SEM).     

Electrochemical impedance spectroscopy; a tool for organic coatings optimizations

Electrochemical impedance spectroscopy (EIS) was applied to the optimization of automotive electrodeposited coatings, container interior coatings and industrial maintenance coatings. The electrochemical impedance data were used to predict corrosion protection, film porosity, solution absorption into the coatings and film delamination properties. Variables such as resin contents, crosslink densities, cure temperatures, and solvent types and contents were evaluated for these various types of coatings. In general the electrochemical impedance data correlated well with conventional exposure tests results such as salt fog, cyclic scab corrosion and delamination tests. The impedance spectra permits a rather rapid (15–75 min per sample) assessment of the film's characteristics even when no visually observable changes have occurred. Electrochemical impedance spectroscopy provides a technique to optimize coatings while reducing the time of coating evaluations and gives insight into the chemical and physical properties of the coatings.     

Electrochemical impedance spectroscopic investigation of adhesion formation mechanism at an epoxy/aluminum interface

A theoretical method for characterizing the structure of a coating/metal interface by electrochemical impedance spectroscopy using water molecules as the probe was established. The properties of coating/metal interfaces for a series of epoxy resins with different water affinities were studied using this method. It was found that as the water affinity of the coating decreased, it became much more difficult for water molecules to reach the coating/metal interface. This suggests that, during the adhesion formation, a more hydrophobic layer is formed along the epoxy/metal interface.     

Electrochemical noise and impedance study of aluminium in weakly acid chloride solution

The electrochemical noise (EN) characteristics of pure aluminium in unbuffered potassium chloride solution and with acetic acid/sodium acetate buffer at pH 5.4 and 4.3 have been analysed to throw light on the influence of pH and of the presence of buffer at the aluminium surface on chloride ion-induced corrosion. Comparison has been made with results obtained by electrochemical impedance spectroscopy (EIS) and quantitative deductions made concerning the values of the noise resistance and the magnitude of the electrochemical impedance. Deviations between results obtained by the two experimental techniques are discussed.     

Electrochemical and anticorrosion performances of zinc-rich and polyaniline powder coatings

In this work, hydrochloride polyaniline (PANI-Cl) powder was incorporated as a conductive pigment into powder zinc-rich primer (ZRP) formulations in order to enhance the electronic conduction paths between zinc particles inside the coating and the steel substrate (i.e. percolation). Coatings were applied onto steel substrates and immersed in a 3% NaCl solution at ambient temperature.The protective properties and electrochemical behaviour of coatings were investigated by monitoring the free corrosion potential versus time and by using EIS. It was found that corrosion potential remains cathodic and constant for a long time up to 100 days of immersion. From EIS results, it was shown that the coatings exhibit larger impedance values than those observed with liquid or other zinc-rich powder formulations containing carbon black. From Raman spectroscopy results, it may be proposed that zinc particles in contact with PANI-Cl pigments were passivated. Other zinc particles remain still active which ensures the cathodic protection of the substrate. Moreover, coatings exhibit good barrier properties.     

Improved electrochemical nucleic acid biosensor based on polyaniline-polyvinyl sulphonate

DNA biosensor based on polyaniline (PANI)-polyvinyl sulphonate (PVS) has been fabricated using electrochemical entrapment technique for detection of organophosphorus pesticides (chlorpyrifos and malathion). These double stranded calf thymus DNA (dsCT-DNA) entrapped PANI-PVS/indium-tin-oxide (ITO) bioelectrodes have been characterized using square wave voltammetry (SWV), Fourier transform infra-red spectroscopy (FT-IR), scanning electron microscopy (SEM) and electrochemical impedance techniques, respectively. These dsCT-DNA entrapped PANI-PVS/ITO bioelectrodes have been found to have response time of 30 s, stability of about 6 months and detection limit for chlorpyrifos and malathion as 0.5 ppb and 0.01 ppm, respectively.     

Interaction between promethazine hydrochloride and DNA and its application in electrochemical detection of DNA hybridization

The interactions of promethazine hydrochloride (PZH) with thiolated single-stranded DNA (HS-ssDNA) and double-stranded DNA (HS-dsDNA) self-assembled on gold electrodes have been studied electrochemically. The binding of PZH with ssDNA shows a mechanism containing an electrostatic interaction, while the mode of PZH interaction with dsDNA contains both electrostatic and intercalative bindings. The redox system belongs to the category of diffusion control approved by cyclic voltammetry (CV). The diffusion coefficients of PZH at the bare, HS-dsDNA and HS-ssDNA modified gold electrodes decrease regularly as 1.34 × 10⁻³ cm² s⁻¹, 1.04 × 10⁻³ cm² s⁻¹, 7.47 × 10⁻⁴ cm² s⁻¹, respectively. The electron transfer standard rate constant k_s of PZH at bare gold, HS-ssDNA and HS-dsDNA modified electrodes are 0.419 s⁻¹, 0.131 s⁻¹, and 0.154 s⁻¹, respectively. The presence of adsorbed dsDNA results in a great increase in the peak currents of PZH in comparison with those obtained at a bare or ssDNA adsorbed gold electrode. The difference between interactions of PZH with HS-ssDNA and HS-dsDNA has been used for hybridization recognition of 14-mer DNA oligonucleotide. The peak current (i_pa) of PZH is linearly proportional to the logarithmic concentration of complementary target DNA in the range from 2.0 × 10⁻⁹ mol L⁻¹ to 5.0 × 10⁻⁷ mol L⁻¹ with the detection limit of 3.8 × 10⁻¹⁰ mol L⁻¹.     

Electrochemical behavior and anticorrosion properties of modified polyaniline dispersed in polyvinylacetate coating on carbon steel

Conducting polyaniline (Pani) was prepared in the presence of methane sulfonic acid (MeSA) as dopant by chemical oxidative polymerization. The Pani-MeSA polymer was characterized by FT-IR, UV-vis, X-ray diffraction (XRD) and impedance spectroscopy. The polymer was dispersed in polyvinylacetate and coated on carbon steel samples by a dipping method. The electrochemical behavior and anticorrosion properties of the coating on carbon steel in 3% NaCl were investigated using open-circuit potential (OCP) versus time of exposure, and electrochemical techniques including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and cyclic voltammetry (CV). During initial exposure, the OCP dropped about 0.35 V and the interfacial resistance increased several times, indicating a certain reduction of the polymer and oxidation of the steel surface. Later the OCP shifted to the noble direction and remained at a stable value during the exposure up to 60 days. The EIS monitoring also revealed the initial change and later stabilization of the coating. The stable high OCP and low coating impedance suggest that the conducting polymer maintains its oxidative state and provides corrosion protection for carbon steel throughout the investigated period. The polarization curves and CV show that the conducting polymer coating induces a passive-like behavior and greatly reduces the corrosion of carbon steel.     

Electrochemical energy storage of Co powders in alkaline electrolyte

The electrochemical charge and discharge behavior of Co powders has been investigated by using X-ray diffraction (XRD), charge and discharge testing, and electrochemical impedance spectroscopy (EIS) at room temperature. Mechanical milling (MM) has been used to treat the Co powders for a comparative experiment. Mechanical milling induces a phase transition of fcc phase to hcp phase, an increase in particle size, and a decrease in grain size. The results of the XRD indicate a reversible reaction between Co and Co(OH)₂. The non-milled Co has a higher discharge capacity at a current density of 60 mA g⁻¹ as compared to the milled one. However, the milled Co presents a better HRD, in spite of the discrepancy in particle size. The results of EIS show that the electrochemical reaction process of Co powders consists of three steps, that is the charge-transfer of Co/Co(OH)₂ or Co/CoH_x, the mass-transfer of HCoO₂⁻, and hydrogen diffusion within Co, depending on the depth of discharge.     

Estimation of kinetic parameters of the passive state of carbon steel in mildly alkaline solutions from electrochemical impedance spectroscopic and X-ray photoelectron spectroscopic data

The unambiguous interpretation of electrochemical impedance spectra of complex systems such as passive metals and alloys in terms of an unique kinetic model is often hampered by the large number of adjustable modeling parameters. In this paper, a combination of in situ electrochemical data and ex situ surface analytical information is employed to validate the estimates of kinetic and transport parameters of the passive state of carbon steel. For the purpose, electrochemical impedance spectroscopic and X-ray photoelectron spectroscopic data for the oxidation of carbon steel in mildly alkaline solutions are quantitatively compared with the predictions of the Mixed-Conduction Model for oxide films that represent the passive oxide as an intermediate phase between magnetite and maghemite. Estimates of the kinetic rate constants at the film interfaces, as well as the diffusion coefficients and field strength in the film are obtained and their relevance for the corrosion mechanism of carbon steel is discussed.