Gold electrodes modified with poly(4‐aminophenol): incorporation of nitrogenated bases and an oligonucleotide

BACKGROUND: Investigations of chemical modification of electrode surfaces and immobilization of nitrogenated bases and oligonucleotides are considered essential for the construction of DNA electrochemical nanodevices. Modification of gold electrode surfaces with poly(4‐aminophenol) was carried out in order to produce polymers capable of immobilizing purine bases and oligonucleotides. RESULTS: Gold electrodes coated with poly(4‐aminophenol) showed improved analytical characteristics and considerably enhanced the electrochemical signals associated with the detection of adenine and guanine by factors of ca 3 and ca 6, respectively, when compared with non‐coated gold surfaces. Impedance studies indicated higher charge transfer impedance to modified electrodes containing adenosine monophosphate. Atomic force microscopy images showed that nitrogenated bases have a strong influence over the morphology of the modified electrode surface. It was observed that the modified electrode containing guanine presents globular morphology. CONCLUSION: The modified electrodes increased the amplitude of the current signal of nitrogenated bases when compared to non‐coated gold surfaces and produced good response and peaks to the detection of an oligonucleotide. This work presents, for the first time, the electropolymerization of 4‐aminophenol on gold electrodes, as well as the detection of nitrogenated bases and an oligonucleotide incorporated on these modified electrodes. Copyright © 2007 Society of Chemical Industry     

A comparative study of electrochemical and biointerfacial properties of acid- and plasma-treated single-walled carbon-nanotube-film electrode systems for use in biosensors

The electrocatalytic and biointerfacial properties of acid- and O₂-plasma-treated single-walled carbon nanotube (SWCNT) electrodes were investigated. The SWCNT-modified electrodes were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance of these electrodes was analyzed by cyclic voltammetry and chronoamperometry. Glucose oxidase was covalently immobilized on the surface of the treated SWCNTs, and the analytical characteristics of the integrated glucose sensor were investigated using glucose as a target analyte. The plasma-activated SWCNT electrode exhibited a much higher sensitivity to the glucose and a lower detection limit than the acid-treated electrode, indicating that a larger amount of enzyme was immobilized on the plasma-treated SWCNT electrode than on the acid-treated electrode. This is due to the fact that the oxygenated functional groups are mainly located at the ends of the tubes in the acid-treated SWCNTs, while the plasma-treated SWCNTs have an even larger surface area available for enzyme immobilization owing to the functional groups covering the entire surface of the SWCNTs.     

纳米金修饰电极的电化学研究

将由柠檬酸三钠与氯金酸制备的纳米金颗粒利用自组装方法修饰于金电极表面形成纳米金修饰电极,运用N5粒度测定仪、透射电子显微镜（TEM）和原子力显微镜（AFM）对纳米颗粒及其修饰电极进行了表征。利用循环伏安法（CV）与交流阻抗法（EIS）研究了纳米金修饰电极的电化学性质。     

Potential and current distributions along resistive electrodes

A simple theory of current and potential distributions along resistive electrodes is re-examined and generalized for non-linearized Tafel behavior. A model of a passivating electrode is discussed and the generalized theory extended to derive expressions for the current and potential profiles along a partially passivated electrode. The relevant expressions permit a predictive analysis of the feasibility of using the electrochemical passivation method for etch-stop control in fabrication of thin, single crystal silicon structures produced by anisotropic deep etching.     

A biosensor platform based on amine functionalized conjugated benzenediamine-benzodithiophene polymer for testosterone analysis

A novel benzenediamine-benzodithiophene polymer is synthesized for use in biosensor fabrication for the detection of testosterone. The sensory platform is constructed via drop coating on a screen-printed carbon electrode, using poly(benzenediamine-Bis[(2-ethylhexyl)oxy]benzodithiophene) (pBDBT) as the polymer layer. Testosterone antibodies are immobilized on the polymer-coated electrode surface via glutaraldehyde, which binds to the surface through the amino functional groups on the polymer backbone. The changes in the surface features due to testosterone binding are investigated via electrochemical techniques such as differential pulse voltammetry, cyclic voltammetry, and electrochemical impedance spectrometry as well as contact angle measurements. Surface morphology of the modified electrodes is characterized by atomic force microscopy. The linear range and limit of detection of the sensor are calculated. Impact of possible interfering compounds is investigated. Furthermore, the sensory platform is utilized for testosterone analysis in synthetic biological fluids.     

Self-assembled gold nanoparticles modified ITO electrodes: The monolayer binder molecule effect

The fabrication of gold attached organosilane-coated indium tin oxide Au_NPs-MPTMS/ITO and Au_NPs-APTES/ITO electrodes [MPTMS = 3-(mercaptopropyl)-trimethoxysilane, APTES = 3-(aminopropyl)-triethoxysilane, ITO = indium tin oxide] was carried out making use of a well-known two-step procedure and the role played by the -SH and -NH₂ functional groups in the two electrodes has been examined and compared using different techniques. Information about particle coverage and inter-particle spacing has been obtained using trasmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) whereas, bulk surface properties have been probed with UV-vis spectroscopy, CV and electrochemical impedance spectroscopy (EIS). The catalytic activity of the two electrodes has been evaluated studying the electrooxidation of methanol in alkaline conditions. The results obtained show that the NH₂ functionality in the APTES binder molecule favours the formation of isle-like Au nanoparticle aggregates that lead to both a higher electron transfer and electrocatalytic activity.     

An investigation of the synergistic effect between magnetite nanoparticles and polypyrrole in nanostructured layer-by-layer films

In this paper, we report the controlled fabrication of layer-by-layer (LbL) films deposited on gold substrates with three different supramolecular architectures using polypyrrole (Ppy) and magnetite nanoparticles (Fe₃O₄-np), besides conventional poly(allylamine hydrochloride) (PAH) e poly(vinyl sulfonic acid) (PVS) polyelectrolytes, demonstrating the synergistic effect between Ppy and Fe₃O₄-np such as a result of their interaction. Modified gold electrodes were analyzed by contact angle (wettability), surface plasmon resonance (SPR), raman spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The (Fe₃O₄-np/Ppy)₃ architecture was also evaluated by scanning electron microscopy. The modified gold electrodes present more homogeneous covering, higher electron transfer and a decrease of resistance with the incorporation of the nanostructured materials such as Ppy and Fe₃O₄-np forming (Fe₃O₄-np/Ppy)₃ LbL film. The results carried out in this study suggest that the (Fe₃O₄-np/Ppy)₃ LbL film can be applied as a possible electrochemical or optical non-enzymatic sensor for analytical detection.     

Electrochemical fabrication and electrocatalytic characteristics studies of gold nanopillar array electrode (AuNPE) for development of a novel electrochemical sensor

Gold nanopillar array electrodes were prepared by electrochemical deposition of gold into the nanopores of anodic aluminum oxide membrane placed onto the gold thin film electrode surface, which was in advance modified with cysteamine self-assembled monolayer as an anchoring layer. The Au nanopillar electrode is electrochemically stable and consists of highly dense, upstanding pillars assembled on the cysteamine monolayer. The structural morphology and chemical composition of the nanoarray electrode was characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. Electrochemical measurements indicate that the Au nanopillar electrode possesses high electrocatalytic activities in the reduction of hydrogen peroxide and molecular oxygen, especially in glucose oxidation due to its higher electroactive surface area. The electro-oxidation studies of several electroactive neurotransmitters demonstrate that the nanopillar electrode can be utilized as a promising material for the construction of novel electrochemical sensor.     

New single-step electrosynthesis process of homogeneous and strongly adherent polypyrrole films on iron electrodes in aqueous medium

Homogeneous and strongly adherent polypyrrole (PPy) films were electrochemically synthesized on iron electrodes in sodium tartrate (Na₂C₄O₆H₄ 0.2 M) aqueous solution. This one step pyrrole electropolymerization process has been successfully achieved under different electrochemical techniques, such as potentiodynamic, galvanostatic and potentiostatic modes. During the first stage of the electrochemical process the tartrate counterion slows down the iron dissolution by leading to the formation of a passivation layer on the working electrode surface, and the pyrrole electropolymerization takes place. The electrosynthesized polymer deposit has been characterized by several microscopic and spectroscopic techniques. Any iron traces have been detected by X-ray photoelectron spectroscopy (XPS) on the outer side of the PPy films, which confirms the compactness and the homogeneity of the polymeric coating. Scanning electronic microscopy (SEM) imaging showed uniform and compact PPy coatings with cauliflower-like structure. Infra-red (IR) and Raman spectroscopies proved that the obtained PPy films have the same vibrational properties as those electrodeposited on noble Pt plates.     

Electrochemical synthesis and characterization of poly(9-benzylfluorene)

In this study, we report the electrochemical polymerization of 9-benzylfluorene (9-BF) in acetonitrile solution. The characterization of the resulting poly(9-BF) film obtained on the working electrode has been performed by using attenuated total reflectance infrared spectroscopy. Besides electrochemical properties, the optical and photoluminescent properties of film were also investigated in detail by means of UV–Vis spectroscopy and fluorescence spectroscopy. Fluorescent spectral studies indicate that polymer film in solid state emits blue-green light at around 470/520 nm under irradiation of UV light. In addition, scanning tunneling microscopy was used to investigate the morphology of poly(9-BF) film. The morphological results also reveal that the surface of single crystalline gold electrode is completely covered with the polymer film.     

Covalent and embedment immobilization of macrocyclic polyamines on gold electrodes and their voltammetric responses towards ethene dicarboxylic acids

In the paper presented, we report on the electrochemical signals generated upon interaction between polyamine host molecules immobilized on the surface of gold electrodes and anions of ethene dicarboxylic acids existing in the aqueous phase.Two methods of gold electrode modification will be compared: covalent (macrocyclic polyamine molecules with -SH groups were bound directly on the gold surface) and embedment (polyamines with long alkyl chains were adsorbed into the monolayer of 1-dodecanethiol deposited on the gold surface).The signals generated due to formation of supramolecular complexes between macrocyclic polyamines and anions of cis- and trans-isomers of ethene dicarboxylic acids at the electrode interface were measured by cyclic voltammetry and Osteryoung square-wave voltammetry with [Ru(NH₃)₆]³⁺ as an electroactive marker.The selectivity and sensitivity of the presented sensors were compared with those ion selective electrodes (ISEs) incorporated with the same and similar macrocyclic polyamines.     

Graphitic Carbon Nitride Decorated with Iron Oxide Nanoparticles as a Novel High-Performance Biomimetic Electrochemical Sensing Platform for Paracetamol Detection

Design and development of new generation smart sensors for medical applications have gained considerable interest of research community in the recent past. In this work, we propose the fabrication of highly sensitive paracetamol sensors-based iron oxide nanoparticles intercalated with graphitic carbon nitride (g-C₃N₄) (GCN) via insitu chemical synthesis. Structural features of the composites were analyzed through SEM, EDX, XRD, FTIR, and UV-Visible spectroscopic techniques. Presence of iron oxide nanoparticles in GCN, significantly improved the conductivity bare GCN from 16 to 125 S cm^?1 due to extended π–π conjugation and large surface area in the composite system. The GCN-Iron oxide (GCN-FO) nanocomposite has been employed as an electrochemical sensing platform for non-enzymatic detection of paracetamol. The electrochemical studies and cyclic voltammetry (CV) results shows that the GCN-FO composite exhibit superior electrochemical properties due to their lower values of the oxidation and reduction potentials. Electrochemical impedance spectroscopy (EIS) studies indicate decreased charge-transfer resistance for iron oxide doped GCN composite in compare to base GCN. The improved electrochemical sensing performance of modified GCN-FO composite electrode is attributed to the formation heterojunctions between iron oxide nanoparticles and GCN. The modified GCN-FO electrodes were employed for non-enzymatic electrochemical detection of PR. The GCN-FO composite electrode shows excellent sensitivity towards PR with a LOD 0.3 μM. Furthermore, the modified GCN-FO electrodes show excellent reproducibility, selectivity, stability and anti-interference performance. Due to its low-cost fabrication, superior electrochemical sensing performance, these modified GCN-FO electrodes could be a promising material for the detection of paracetamol at low concentrations.

     

The underlying electrode causes the reported ‘electro-catalysis’ observed at C60-modified glassy carbon electrodes in the case of N-(4-hydroxyphenyl)ethanamide and salbutamol

The reported ‘electro-catalysis’ of C₆₀-film-modified electrodes for the electrochemical oxidation of N-(4-hydroxyphenyl)ethanamide and salbutamol has been explored at boron-doped diamond and glassy carbon electrodes. Using both C₆₀-film-modified boron-doped diamond and glassy carbon as underlying electrode substrates no electro-catalytic response is observed using the target analytes but rather the C₆₀ serves to block the electrode surface.A common experimental protocol used by researchers in this field is to electrochemically pre-treat the C₆₀-film-modified electrode. The response of employing this electrochemical pre-treatment at both bare glassy carbon and boron-doped diamond electrodes using the target analytes reveals that no effect on the electrochemical responses obtained at the boron-doped diamond electrode whereas a slight but significant effect occurs on glassy carbon which is attributed to the likely introduction of surface oxygenated species.Consequently the previously reported ‘electro-catalysis’ using C₆₀-film-modified electrode is not due to C₆₀ itself being catalytic, but rather that substrate activation through electrode pre-treatment is responsible for the observed ‘electro-catalysis’ likely through the introduction of surface oxygenated species.This work clearly shows that substrate activation is an important parameter which researchers studying C₆₀-film-modified electrodes, especially in electro-analysis needs to be considered.     

Improved performance of iron-chromium flow batteries using SnO2-coated graphite felt electrodes

Polyacrylonitrile-based graphite felt has the properties of high temperature resistance, corrosion resistance, low thermal conductivity, large surface area and excellent electrical conductivity. It has become the preferred material for flow battery electrodes, but its chemical activity is poor. In order to improve the electrochemical activity of graphite felt electrodes, the electrodes were prepared by SnO₂-coated graphite felt. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microscopic morphology of SnO₂-coated graphite felt electrodes. Electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge tests were performed using an electrochemical workstation to investigate the electrocatalytic activity of SnO₂-coated graphite felt electrodes and their cell performance. The results show that the SnO₂ coating on the graphite felt surface forms a convex and concave microstructure, which further increases the specific surface area of the electrode, and at the same time successfully introduces oxygen-containing functional groups to the electrode surface, increasing the electrochemically active spots on the surface. In addition, the presence of oxygen defects in the SnO₂ crystal structure provides more electrochemically active sites and improves the electrochemical performance of the graphite felt electrode. At a current density of 142 mA cm^?2, the charge-discharge capacity of the battery assembled with the SnO₂-coated graphite felt electrode was significantly improved; when the current density was 250 mAcm^?2, the Coulombic efficiency of the electrode (TGF-2) coated with a concentration of 0.1 M could reach 84%.     

The oxidation of carbon monoxide at platinum and gold metallized membrane electrodes

The oxidation of carbon monoxide at gold platinum membrane electrodes is discussed and it is shown that the electrochemical characteristics of these electrodes are similar to massive electrodes. At platinum the short time response is determined by the oxidation of a surface monolayer of carbon monoxide by a reactant pair mechanism occuring at the edges of growing islands of an oxidised platinum species whilst at gold, the process is diffusion controlled. On both metals the longer timescale response is complicated by poisoning of the surface by a reaction intermediate but it is also shown that a gold anode may be reactivated by potential cycling. The relevance of these results to the construction of an analytical device is discussed.     

Electrochemical and photoelectrochemical behaviour of passivated niobium electrodes during hydrogen evolution

The electrochemical and photoelectrochemical behavior of niobium electrodes passivated in 0.5 M H₂SO₄ and 1 M HNO₃ has been investigated. High intensity pulse lasers were used as light sources. This technique allows photoelectrochemical measurements with light wavelengths smaller than the band gap of the semiconducting passive film. The donor concentration and the flat band potential of the passive films were calculated from capacity measurements. The effect of cathodic hydrogen evolution on the behaviour of the oxide film formed was found to depend on the time of the cathodic treatment of the electrode. The results showed that the behaviour of the passive film formed on niobium in nitric acid is different from that formed in sulphuric acid. The calculated donor concentrations and the extrapolated flat band potentials indicate that the nature of the passive film depends on the formation medium. The adsorption of hydrogen on the passivated Nb-electrode up to a time limit of 1 ms could be traced using photocharge measurements with excitation energies less than the band gap energy of the semiconducing oxide film.     

Active nano-CuPt3 electrocatalyst supported on graphene for enhancing reactions at the cathode in all-vanadium redox flow batteries

Graphene-supported monometallic (Pt) and bimetallic (CuPt₃) cubic nanocatalysts have been investigated as new positive electrode materials for improving the VO₂⁺/VO²⁺ redox process occurring in the vanadium redox flow batteries (VRB). High-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) have been employed to characterize the electrodes. The presence of the CuPt₃ nanocubes on graphene conferred higher electrocatalytic activity due to the much higher electroactive area compared to that obtained with the Pt nanoparticles. The electrochemical surface area of the nano-(CuPt₃)-decorated graphene electrode was 105% higher compared to non-decorated graphene, being then a promising alternative for improving the VRB.     

On the fractal study of LiMn2O4 electrode surface

Fractal dimension of a LiMn₂O₄ electrode prepared by sol-gel method was determined using electrochemical techniques based on the phenomenon of “diffusion towards electrode surface”. A simple discussion was made on the methodology to understand what is really estimated as the fractal dimension. It was demonstrated that the value of fractal dimension determined based on electrochemical methods is strongly dependent on the electrochemical system situation. This is generally true for all real electrodes involving insertion/extraction processes. This comes from the fact that surface morphology of the electrode is subject of significant changes during the electrochemical experiment.     

Electrochemical oxidation of ammonia (NH4/NH3) on thermally and electrochemically prepared IrO2 electrodes

The electrochemical oxidation of ammonia (NH₄⁺/NH₃) in sodium perchlorate was investigated on IrO₂ electrodes prepared by two techniques: the thermal decomposition of H₂IrCl₆ precursor and the anodic oxidation of metallic iridium. The electrochemical behaviour of Ir(IV)/Ir(III) surface redox couple differs between the electrodes indicating that on the anodic iridium oxide film (AIROF) both, the surface and the interior of the electrode are electrochemically active whereas on the thermally decomposed iridium oxide films (TDIROF), mainly the electrode surface participates in the electrochemical processes.On both electrodes, ammonia is oxidized in the potential region of Ir(V)/Ir(IV) surface redox couple activity, thus, may involve Ir(V). During ammonia oxidation, TDIROF is deactivated, probably by adsorbed products of ammonia oxidation. To regenerate TDIROF, it is necessary to polarize the electrode in the hydrogen evolution region. On the contrary, AIROF seems not to be blocked during ammonia oxidation indicating its fast regeneration during the potential scan. The difference between both electrodes results from the difference in the activity of the iridium oxide surface redox couples.     

Nano-crystalline diamond electrodes with cap layer decorated by gold particles

We describe the electrochemical characteristics of a nano-crystalline diamond (NCD) electrode with a thin (～ 60 nm) low-doped cap layer on a highly boron-doped diamond contact layer, where the grain boundary areas of the surface are decorated by gold particles by electroplating. The presence of the surface cap layer leads to a reduced background current compared to the highly doped NCD electrodes. At the same time, the electrical resistance to the gold particles via grain boundary defects of the cap layer does not limit the activity of the particles in 0.1 M H₂SO₄ electrolyte. The equivalent circuit of the decorated cap-layer electrodes is discussed using the results of electrochemical impedance spectroscopy and data on gold–diamond Schottky diodes fabricated on identical NCD layers. This equivalent circuit can be reduced to a low number of key elements, which could be useful for optimizing such electrodes for high sensitivity/low noise applications.