Search

Reliable and accurate in situ sensors capable of detecting and quantifying troublesome marine biofilms on metallic surfaces are increasingly necessary. A 0.2 mm diameter gold electrochemical sensor was fully characterized using cyclic voltammetry in abiotic and biotic artificial seawater media within a continuous culture flow cell to detect the growth and development of an aerobic Pseudoalteromonas sp. biofilm. Deconvolution of the abiotic and biotic responses enable the constituent extracellular electron transfer and biofilm responses to be resolved. Differentiation of enhanced oxygen reduction kinetics within the aerobic bacterial biofilm is linked to enzyme and redox mediator activities.

An electrochemical switching strategy is presented for the sensitive determination of Staphylococcus enterotoxin B (SEB). It is based on the use of DNA triangular pyramid frustum nanostructure (TPF DNA ) consisting of (a) three thiolated probes, (b) one auxiliary probe, and (c) an aptamer against SEB. The TPF DNA was assembled on the gold electrode, with the SEB aptamer designed on top of the TPF DNA . The electron transfer to hexacyanoferrate acting as an electrochemical probe is strongly inhibited in the TPF DNA -modified electrode. This is assumed to be due to the formation of a 3D TPF DNA structure that limits access of hexacyanoferrate to the electrode. Therefore, the Faradaic impedance is large. However, in the presence of SEB, it will bind to the aptamer and dehybridize the hybrid formed between aptamer and its complementary sequence. As a result, the TPF DNA nanostructure changes to an equilateral triangle DNA nanostructure. This results in a more efficient electron transfer and a smaller Faradaic impedance. The method has a detection limit of 0.17 ng mL -1 of SEB (at an S/N of 3) and a dynamic range that covers the 0.2-1000 ng mL -1 concentration range. The applicability and reliability of the method was demonstrated by anayzing (spiked) milk samples, and the results were compared to those obtained with an ELISA kit. The relative standard deviations between the two methods range between -6.59 and 9.33%. Graphical abstract An electrochemical switching strategy is presented for the sensitive detection of Staphylococcus enterotoxin B based on 3D DNA structure conversion of nanostructure from triangular pyramid frustum to equilateral triangle.

An electrochemical sensor is described for the determination of microRNA-21 by combing the DNA generated current with target-triggered hybridization chain reaction (HCR). A thiol-modified hairpin capture probe was first immobilized on a gold electrode. In the presence of microRNA-21, hybridization leads to a conformational change of the capture probe. The conformational change triggers HCR to generate a long DNA strand on the surface of the electrode. The phosphate backbone of the long DNA strand then reacts with molybdate to form the redox redox probe molybdophosphate, and this generates an electrochemical current. The HCR triggered by microRNA increases the amount of phosphate groups due to the extension of the DNA length, and thus increases the response current. The electrode, best operated at a voltage of 0.20 V, was successfully applied to the analysis of microRNA-21 in (spiked) human serum samples. In our perception, it represents a promising tool for analyzing a variety of microRNA biomarkers. Graphical abstract Electrochemical sensor for detection of microRNA-21 by combing the DNA generated electrochemical current concept with target-triggered hybridization chain reaction (HCR) strategy is reported. DNA strands (S1 and S2) were assembled onto electrode through HCR reaction. MCH: 6-mercapto-1-hexanol.

Due to the negative impact of nitrate and nitrite on human health, their presence exceeding acceptable levels is not desired in foodstuffs. Thus, nitrite determination at low concentrations is a major challenge in electroanalytical chemistry, which can be achieved by fast, cheap, and safe electrochemical sensors. In this work, the working electrode (Au) was functionalized with p-aminothiophenol (p-ATP) and modified with gold nanoparticles (Au-NPs) to manufacture the final (Au/p-ATP-Aunano) electrode in a two-step procedure. In the first step, p-ATP was electropolymerized on the electrode surface to obtain a polyaminothiophenol (PATP) coating. In the second step, Au/p-ATP-Aunano working electrode was prepared by coating the surface with the use of HAuCl₄ solution and cyclic voltammetry. Determination of aqueous nitrite samples was performed with the proposed electrode (Au/p-ATP-Aunano) using square wave voltammetry (SWV) in pH 4 buffer medium. Characteristic peak potential of nitrite samples was 0.76 V, and linear calibration curves of current intensity versus concentration was linear in the range of 0.5-50 mg·L(-1) nitrite with a limit of detection (LOD) of 0.12 mg·L(-1). Alternatively, nitrite in sausage samples could be colorimetrically determined with high sensitivity by means of p-ATP‒modified gold nanoparticles (AuNPs) and naphthylethylene diamine as coupling agents for azo-dye formation due to enhanced charge-transfer interactions with the AuNPs surface. The slopes of the calibration lines in pure NO₂(-) solution and in sausage sample solution, to which different concentrations of NO₂(-) standards were added, were not significantly different from each other, confirming the robustness and interference tolerance of the method. The proposed voltammetric sensing method was validated against the colorimetric nanosensing method in sausage samples.

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 0.25 mol L(-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(-6) mol L(-1) of furosemide. The detection limit was obtained as 7.0×10(-8) mol L(-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., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Using the concept of electrogenerated chemiluminescence (ECL), a sensitive analytical method for the determination of carbidopa is described. Electro-oxidation of carbidopa on the surface of a graphene oxide (GO)-modified gold electrode (GE) leads to enhancement of the weak emission of oxidized luminol. Under optimum experimental conditions, the ECL signal increases linearly with increasing carbidopa concentrations over a range of 1.0 × 10(-9) -1.7 × 10(-7)  M, with a detection limit of 7.4 × 10(-10)  M. The proposed ECL method was successfully used for the determination of carbidopa in urine samples., (Copyright © 2014 John Wiley & Sons, Ltd.)

The electrochemical oxidation of bio‐based 5‐hydroxymethylfurfural (HMF) results in 2,5‐furandicarboxylic acid (FDCA), which is a renewable and environmentally friendly alternative to terephthalic acid. Using a gold electrode, we compare the electrochemical oxidation of the aldehyde and alcohol functionality in HMF to the isolated functionalities represented by ethanol and acetaldehyde. Thereby, we investigate the effect of the inert furan ring on the electrochemical reaction. The linear sweep voltammogram (LSV) of HMF in a weakly adsorbing electrolyte differs only marginally from the superposition of LSVs obtained in ethanol and acetaldehyde containing electrolytes. However, in the presence of strong adsorbates, only the kinetics of ethanol and acetaldehyde oxidation but not of HMF oxidation are hampered. We assign this to a stronger adsorption of HMF through the furan ring than through the alcohol and carbonyl functionality of ethanol and acetaldehyde. Hence, HMF is better equipped to compete for adsorption sites than aliphatic compounds. [ABSTRACT FROM AUTHOR]

Abstract The electrochemical oxidation of bio‐based 5‐hydroxymethylfurfural (HMF) results in 2,5‐furandicarboxylic acid (FDCA), which is a renewable and environmentally friendly alternative to terephthalic acid. Using a gold electrode, we compare the electrochemical oxidation of the aldehyde and alcohol functionality in HMF to the isolated functionalities represented by ethanol and acetaldehyde. Thereby, we investigate the effect of the inert furan ring on the electrochemical reaction. The linear sweep voltammogram (LSV) of HMF in a weakly adsorbing electrolyte differs only marginally from the superposition of LSVs obtained in ethanol and acetaldehyde containing electrolytes. However, in the presence of strong adsorbates, only the kinetics of ethanol and acetaldehyde oxidation but not of HMF oxidation are hampered. We assign this to a stronger adsorption of HMF through the furan ring than through the alcohol and carbonyl functionality of ethanol and acetaldehyde. Hence, HMF is better equipped to compete for adsorption sites than aliphatic compounds.

A voltammetric technique for electrochemical sensing and quantification of granulocytosis risk inducing metabolite of aminopyrine, 4-Aminoantipyrine (4-AAP) at gold electrode has been developed. The gold electrode shows excellent selectivity and sensitivity towards the oxidation of 4-AAP in phosphate buffer solution (PBS) of pH=3.0. It is observed from the electrochemical studies of scan rate that overall electrode process is diffusion controlled and pH effect suggests involvement of protons in electrochemical oxidation of 4-AAP. A linear current response towards the electrochemical oxidation of 4-AAP in the concentration range of 1.0 × 10-6 - 2.5 × 10-5 M is observed with limit of detection of 3.8 × 10-8 M (S/N = 3). The interference studies have shown that the gold electrode exhibited excellent selectivity in presence of large excess of interferents. The method is employed to recovery study of 4-AAP in spiked urine and serum samples. [ABSTRACT FROM AUTHOR]

Supported lipid membranes are widely used platforms which serve as simplified models of cell membranes. Among numerous methods used for preparation of planar lipid films, self-assembly of bicelles appears to be promising strategy. Therefore, in this paper we have examined the mechanism of formation and the electrochemical properties of lipid films deposited onto thioglucose-modified gold electrodes from bicellar mixtures. It was found that adsorption of the bicelles occurs by replacement of interfacial water and it leads to formation of a double bilayer structure on the electrode surface. The resulting lipid assembly contains numerous defects and pinholes which affect the permeability of the membrane for ions and water. Significant improvement in morphology and electrochemical characteristics is achieved upon freeze–thaw treatment of the deposited membrane. The lipid assembly is rearranged to single bilayer configuration with locally occurring patches of the second bilayer, and the number of pinholes is substantially decreased. Electrochemical characterization of the lipid membrane after freeze–thaw treatment demonstrated that its permeability for ions and water is significantly reduced, which was manifested by the relatively high value of the membrane resistance.

Abstract: 3D printing (additive manufacturing) is currently an emerging technology that could revolutionize the traditional manufacturing process. The application of 3D printing technology has been examined in many different fields including manufacturing, science, medicine, and electronics. Another application of 3D printing technology which holds promising potential is fabrication of electrochemical sensors and transducers. Electroanalytical devices hold advantages such as low cost, portability, ease of use, and rapid analysis. Here we examined the feasibility of utilizing 3D‐printed metal electrodes for the electrochemical detection of the pain reliever acetaminophen (AC) also known as paracetamol and the neurotransmitter dopamine (DA) in aqueous solutions. 3D‐printed stainless steel helical‐shaped electrodes were tested before and after surface modification by electro‐plating with a thin gold film (3D gold). [ABSTRACT FROM AUTHOR]

Lipopeptides are known to show bactericidal activity and due to their simple structure, ease of design, and low cost of implementation, they are often considered potent replacement for many traditional antibiotics. Another important advantage of lipopeptides is related to the fact that their preferential target is a cell membrane. Hence their action is less specific than conventional antibiotics, which means that development of drug resistance by pathogens is less probable in such case. In this paper we have utilized electrochemical methods and in situ atomic force microscopy to evaluate the mode of action of novel lipopeptide C 15 H 31 CO-DPhe-Dab-Dab-Leu-NH 2 on planar lipid bilayer. The latter was composed of phosphatidylethanolamines and phosphatidylglycerols extracts from E. coli . Therefore it can be considered as a simplified model of inner membrane of Gram negative bacteria. We have found that lipopeptide-lipid interactions strongly affect molecular organization of PE/PG bilayer, which is reflected by increased disorder and subsequent perforation of the film. Importantly, fluid domains were identified as preferential sites for insertion of lipopeptide molecules, which tend to accumulate within the membrane. However, above certain threshold ratio the membrane becomes swollen and strongly destabilized. This results in membrane rupture and large mixed lipopeptide-lipid aggregates departure from electrode surface. Based on experimental observations, the mechanism of C 16 -fXXL action on bacterial-like model membrane is proposed. [ABSTRACT FROM AUTHOR]

We propose a novel voltammetric analysis method for the targeted nucleic acid quantification using electrochemical DNA chip and digital loop-mediated isothermal amplification (LAMP), which is based on the most probable number (MPN) method. We designed the position of electrodes (30 regions) on the DNA chip surface at 2 mm intervals in the flow channel. Since the LAMP reaction is carried out at constant temperature, it is supposed that the motions of both the targeted nucleic acid and amplicon in the LAMP solution are diffusion-limited. So an independent volume is formed around the electrode (like a test tube). MPN for a single dilution with any positive electrodes was given by MPN (μL − 1 ) = 1 / m e × 2.303 × log ((number of total electrode) / (number of negative electrode)). The m e denotes the amount of sample in each volume covered by an electrode on the DNA chip. When different concentrations of targeted nucleic acid were amplified, all electrodes on the DNA chip were positive above 2 × 10 1 copies/μL. On the other hand, positive ratios of detection decreased to 25% and 88% at 2 × 10 − 1 and 2 × 10 0 copies/μL, respectively. From these results, the volume covered by an electrode in the flow channel was calculated to be 1.2 ± 0.2 μL. The MPN method is applicable to nucleic acid analysis using electrochemical DNA chip and several copies of targeted nucleic acid are quantified precisely without calibration curve. [ABSTRACT FROM AUTHOR]

We have developed a novel voltammetric DNA chip for real-time electrochemical detection of targeted nucleic acid sequences using loop-mediated isothermal amplification (LAMP) and ruthenium hexaamine (RuHex) as the intercalative redox compound. A GspSSD DNA polymerase was used for LAMP owing to its tolerance of the intercalative redox compound. The electrochemical reaction of 1 mM RuHex in the LAMP solution was measured continuously by linear sweep voltammetry at 65 °C using an electrochemical DNA chip. According to the LAMP reaction of the positive sample, the cathodic peak current of RuHex increased and the cathodic peak potential of RuHex shifted to negative voltage. The initial number of copies of the targeted nucleic acid was correlated with both the time when the cathodic current began to increase and the time when the cathodic potential began to shift rapidly. 10 3 to 10 6 copies/50 μL of the targeted nucleic acid were detected quantitatively and the detection limit was 10 1 copies within an hour. We expect these results to lead to the realization of simple and stable electrochemical real-time monitoring of targeted nucleic acids while also facilitating the implementation of electrochemical DNA chips in molecular testing. [ABSTRACT FROM AUTHOR]

Heavy metals, being one of the most toxic and hazardous pollutants in natural water, are of great public health concern. Much effort is still being devoted to the optimization of the electroanalytical methods and devices, particularly for the development of novel electrode materials in order to enhance selectivity and sensitivity for the analysis of heavy metals. The ability of 3D-printing to fabricate objects with unique structures and functions enables infinite possibilities for the creation of custom-made electrochemical devices. Here, stainless steel 3D-printed electrodes (3D-steel) have been tested for individual and simultaneous square wave anodic stripping analysis of Pb and Cd in aqueous solution. Electrodeposition methods have also been employed to modify the steel electrode surface by coating with a thin gold film (3D−Au) or a bismuth film (3D−Bi) to enhance the analytical performance. All 3D-printed electrodes (3D-steel, 3D−Au and 3D−Bi) have been tested against a conventionally employed glassy carbon electrode (GC) for comparison. The surface modified electrodes (3D−Au and 3D−Bi) outperformed the GC electrode demonstrating higher sensitivity over the studied concentration ranges of 50-300 and 50-500 ppb for Pb and Cd, respectively. Owing to the bismuth property of binary alloys formation with heavy metals, 3D−Bi electrode displayed well-defined, reproducible signals with relatively low detection limits of 3.53 and 9.35 ppb for Pb and Cd, respectively. The voltammetric behaviour of 3D−Bi electrode in simultaneous detection of Pb and Cd, as well as in individual detection of Pb in tap water was also monitored. Overall, 3D-printed electrodes exhibited promising qualities for further investigation on a more customizable electrode design. [ABSTRACT FROM AUTHOR]

Determination of fluoroquinolones (FQs) in foodstuffs and environment is of great importance. In this study, a novel electrochemical sensing method was developed for rapid, highly sensitive and specific detection of FQs, based on aptamer (Apt) as molecular recognition probe, single-stranded DNA-binding protein (SSB) as a physical and negatively charged barrier for the access of redox probe ([Fe(CN) 6 ] 3−/4− ) to the surface of gold electrode. The designed electrochemical aptasensor needs less than 1 h for detection of ciprofloxacin. In the absence of ciprofloxacin, SSB interacts with Apt and restricts the access of redox probe to the surface of electrode, leading to a weak current signal. In the presence of target, SSB could not bind to the Apt, resulting in more access of redox probe to the surface of electrode and a strong current signal. The designed electrochemical sensor exhibited high specificity toward FQs with a limit of detection (LOD) as low as 263 pM for ciprofloxacin. Moreover, the developed sensing method was successfully applied for determination of ciprofloxacin in serum, milk and water samples with LODs of 336, 351 and 261 pM, respectively. [ABSTRACT FROM AUTHOR]

In this research, electrochemical and spectroelectrochemical behaviors of acrylamide (AA) have been studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Cyclic voltammetric studies of AA in acetonitrile (CH3CN) containing 100 mM tetrabutylammonium tetrafluoroborate (NBu4BF4) on glassy carbon (GC) electrode was performed between 0.0 mV and +2600 mV potential range, on platinum (Pt) electrode was performed between 0.0 mV and +1500 mV potential range and gold (Au) electrode was performed between +600 mV and +2200 mV potential range at 100 mVs-1 scan rate with 10 cycles. The surface characterization process was carried out using CV and EIS technique in both aqueous and non-aqueous media. [ABSTRACT FROM AUTHOR]

An electrochemical sensor for nonenzymatic hydrogen peroxide (H 2 O 2 ) detecting based on size controllable preparation of gold nanoparticles (Au) loading on graphene sheets@cerium oxide (GS@CeO 2 ) nanocomposites modified gold electrode (GE) was fabricated. The GS@CeO 2 nanocomposites were prepared via a facile solvothermal process. Different sizes of Au were controllably prepared and homogenously loaded on the surface of GS@CeO 2 nanocomposites modified GE using a simple electroless plating method. X-ray powder diffractometer (XRD) combines with Fourier transform infrared spectrum (FTIR) were used to characterize the composition of GS@CeO 2 nanocomposites. Electrochemical impedance spectroscopy (EIS) was utilized to study the interfacial properties as well as Field emission scanning electron microscopy (FESEM) was employed to characterize the morphologies of different electrodes. The electrochemical properties of electrochemical sensor were investigated by cyclic voltammetry (CV) and i-t curve methods. After all experimental parameters were optimized, the GS@CeO 2 /Au hybrid nanomaterials modified GE (GE ǀ GS@CeO 2 /Au) showed a good performance towards the electrocatalytic reduction of H 2 O 2 . A wide linear detection range (LDR) of CV peaks from 1.0 × 10 −3 mM to 10.0 mM ( R 2 = 0.9990) and a low limit of detection (LOD) of 2.6 × 10 −4 mM (S/N = 3) was achieved. The proposed electrochemical sensor was quick, selective, sensitive, simple, stable and reliable to quantitative determination of trace H 2 O 2 in contact lens care solutions. [ABSTRACT FROM AUTHOR]

The aim of our work was to synthetize of a new analogue of abiraterone—thiolated abiraterone (HS-AB) and design a gold surface monolayer, bearing in mind recent advances in tuning monolayer structures and using them as efficient drug delivery systems. Therapeutic self-assembled monolayers (TSAMs) were prepared by chemically attaching HS-AB to gold surfaces. Their properties were studied by voltammetry and atomic force microscopy (AFM). A gold electrode with immobilized thioglycolic acid (HS-GA) was used for comparison. The surface concentration of HS-AB on the gold surface was 0.572 nmol/cm2, determined from the area of the voltammetric reduction peaks (desorption process). The area per one molecule estimated from the voltammetry experiments was 0.291 nmol/cm2. The capacity of thus prepared electrode was also tested. The calculated capacity for the HS-AB modified electrode is 2.90 μF/cm2. The obtained value indicates that the monolayer on the gold electrode is quite well ordered and well-packed. AFM images show the formation of gold nanoparticles as a result of immersing the HS-AB modified gold electrode in an aqueous solution containing 1 mM HAuCl4·3H2O. These structures arise as a result of the interaction between the HS-AB compound adsorbed on the electrode and the AuCl4− ions. The voltammetric experiments also confirm the formation of gold structures with specific catalytic properties in the process of oxygen reduction.

Methotrexate (MTX), a common pharmaceutical drug in cancer therapy and treatment of rheumatic diseases, is known to cause severe adverse side effects at high dose. As the side effect may be life threatening, there is an urgent need for a continuous, bed-side monitoring of the nominal MTX serum level in a patient while the chemical is being administered. This article describes a detection of MTX using a flow system that consists two modified gold electrodes. Interaction of MTX with the antibodies fixed on the electrode surface is detected by electrochemical impedance spectroscopy and evaluated using singular value decomposition (SVD). The key finding of this work is that the change in the electrode capacitance is found to be quantitative with respect to the concentration of MTX. Moreover a calibration curve constructed using the principal component regression method has a linear range of six orders of magnitude and a detection limit of 1.65 × 10 −10 M. [ABSTRACT FROM AUTHOR]

Cocaine is one of the most commonly abused stimulant which could affect the central nervous system. In this work, an electrochemical aptasensor was designed for sensitive and selective detection of cocaine, based on complimentary strands of aptamer (CSs), H-shape structure of Aptamer (Apt)-CSs conjugate and gold electrode. This aptasensor inherits properties of gold such as high electrochemical conductivity and large surface area, as well as high selectivity and sensitivity of aptamer toward its target and property of H-shape structure of Apt-CSs conjugate to act as a gate for the access of redox probe to the surface of electrode. In the absence of cocaine, the gate is closed, so that the electrochemical signal is weak. In the presence of cocaine, aptamer binds to target, leaves the surface of electrode and the gate is opened, leading to a strong electrochemical signal. The fabricated electrochemical aptasensor exhibited good selectivity toward cocaine with a limit of detection (LOD) as low as 0.228 nM. Furthermore, the designed aptasensor was successfully used to detect cocaine in serum with a LOD as low as 0.273 nM. [ABSTRACT FROM AUTHOR]

Study of biophysical interactions have been carried out using specific combination of proteins such as human IgG (as antigen) and anti-human IgG (as complementary antibody; raised in rabbit). Bovine serum albumin (BSA) was used to block any nonspecific interaction between antigen and antibody as BSA has been reported to bind to several sites non-specifically. Optimization of BSA concentration was done in order to make the antigen-antibody interaction relatively more pronounced and specific. We have used gold electrode in order to provide a relatively inert platform for adsorption/immobilization of protein molecules. The interaction between the antigen and antibody caused an increase in the charge transfer resistance (parallel resistance in Randles cell model) for an indicator molecule (hexacyanoferrate) and this was monitored by impedance spectroscopy. Detection limit for the antigen was found to be about 50 ng/mL. The approach presented is general and versatile and can be used for any antigen-antibody pair without any significant modification. [ABSTRACT FROM AUTHOR]

The electrochemical behavior of Fe(III) in the presence of phytate ligand was investigated by cyclic voltammetry on the polycrystalline gold and mercury drop electrodes in the pH range between 1.5 and 10, and ligand to metal molar ratio from 0 to 20. Complexation of Fe(III) and Fe(II) by phytate ligand (L) reflects in (i) shift of the formal potential E 0′ of the Fe(III)/Fe(II) redox couple into the negative direction, and (ii) an increased irreversibility of the redox processes. Change of the formal potential originate from higher stability of the Fe(III)L complex with respect to Fe(II)L complex, however, due to the slow charge transfer control of the redox processes apparent stability constants calculated from voltammetric data may lead to an overestimation of their true values. Irreversible reduction of Fe(III)L to Fe(II)L is diffusion controlled and involves one proton per one electron on both electrodes. Reduction of Fe(III) phytate complex to Fe(II)L depends on the pH and at pH < 5 proceeds via [Fe III H 5 L] 4– species, but at higher pH less protonated [Fe III H 3 L] 6– become the major reacting species. An almost stepwise change of the reduction peak potential for more than 0.8 V into the negative direction around pH 5 indicate that both reactants have quite different stability and/or structure. We predicted that electronic configuration and affinity of Fe(III) ions for the octahedral coordination induce the inversion of phytate ligand from its equatorial to the axial conformation which form more than ten orders of magnitude more stable Fe(III)L complexes. Fe(II)L intermediate generated on the electrode is strongly adsorbed on both gold and mercury electrodes, and totally irreversible reduction of Fe(II)L complex to the Fe metal was observable at mercury electrode as well. From Fe(III/II)L peak analysis on the mercury electrode the cathodic charge transfer coefficient of 0.68 was found, for [Fe III H 3 L] 6– reacting species the diffusion coefficient of (9.1 ± 0.1) × 10 −7 cm 2 /s was estimated, and the rate constant k 0 of 7.8 × 10 −5 cm/s was calculated. [ABSTRACT FROM AUTHOR]

The effect of gold substrate surface charge (potential) on adsorptive/desorptive behaviour of fibrinogen (FG) was studied by employing differential capacitance (DC) and polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), in terms of FG adsorption thermodynamics, kinetics, and desorption kinetics. The gold substrate surface charge was modulated in-situ within the electrochemical double-layer region by means of electrochemical potentiostatic polarization in a FG-containing electrolyte, thus avoiding the interference of other physico-chemical properties of the gold surface on FG’s interfacial behaviour. The FG adsorption equilibrium was modeled using the Langmuir isotherm. Highly negative values of apparent Gibbs free energy of adsorption (ranging from from −52.1 ± 0.4 to −55.8 ± 0.8 kJ mol −1 , depending on the FG adsorption potential) indicated a highly spontaneous and strong adsorption of FG onto the gold surface. The apparent Gibbs free energy of adsorption was found to be independent of surface charge when the surface was negatively charged. However, when the gold surface was positively charged, the apparent Gibbs free energy of adsorption exhibited a pronounced linear relationship with the surface charge, shifting to more negative values with an increase in positive electrode potential. The adsorption kinetics of FG was also found to be dependent on gold surface charge in a similar manner to the apparent Gibbs free energy of adsorption. It was suggested that the driving force for the adsorption of FG on a negatively charged surface represents a positive gain in the entropy of the system, whereas the adsorption on a positively charged gold surface was found to be controlled by electrostatic forces. FG desorption measurements revealed that when the gold surface is polarized within the electrochemical double-layer region during the desorption process, the protein desorption kinetics is rather slow. However, within the regions of hydrogen and oxygen evolution, the FG desorption kinetics accelerates significantly, due to the physical removal of the adsorbed protein layer by gas bubbles evolving from the substrate surface, which enables a complete removal of the pre-adsorbed FG layer. The latter could potentially be employed for electrochemical cleaning of electrically-conducting surfaces fouled by adsorbed protein layers (heat exchangers, filtration membranes, etc.). [ABSTRACT FROM AUTHOR]

This review discusses different approaches that have been taken to mimic oxidative drug metabolism as executed by members of the Cytochrome P450 (CYP450) family of enzymes in humans. Non-modified electrodes can be used to produce some of the oxidative drug metabolites observed in vivo but their scope is rather limited. Modifying electrodes with simple cofactors in analogy to those observed in CYP450 but without the protein scaffold extends these possibilities and notably allows driving reactions following a CYP450-like mechanism. The review ends with approaches to immobilize CYP450s or analogs thereof on electrodes to mimic the in vivo drug metabolism fully. We discuss future perspectives with respect to the advantages and the disadvantages of each level of complexity and possible ways forward. [ABSTRACT FROM AUTHOR]

Phenytoin (5,5-diphenylhydantoin), one of the most frequently used anticonvulsant and antiarrhythmic drugs, was examined and determined at bare gold electrode in 0.05 M NaHCO 3 using its anodic activity by cyclic voltammetry (CV) and square wave voltammetry (SWV). Gold electrode is highly sensitive to the phenytoin concentration (the investigated level of concentrations is usually found in human serum of patients treated with phenytoin), providing linear relationships for a set of lower concentrations (0.5, 0.6, 0.8, 1.0 μmol dm −3 ) and for a set of higher concentrations (10, 20, 30, 40, 50 μmol dm −3 ). The effects of the substituent on the phenyl rings on the electrochemical behavior of two derivatives, 5,5-di(4-chlorophenyl) hydantoin and 5,5-di(4-methylphenyl) hydantoin, were examined by CV. A computational study in correlation with the experimental voltammetric results enabled to propose the oxidation mechanisms: the investigated compounds undergo oxidation involving transfer of 1e – and 1 proton by irreversible, diffusion controlled process. [ABSTRACT FROM AUTHOR]

Micro-nano structured Cu-Co was in situ fabricated on the surface of a gold electrode via electrochemical reduction of CuCl and Co(NO). It is shown that the shape of the particles can be controlled by variation of deposition current, deposition time, pH value and the ratio of Cu(II) and Co(II) ions. If prepared under current of −200 μA in 0.1 M, pH 4.0 acetate buffer solution, the film possesses high catalytic activity towards the electrochemical oxidation of glucose at a largely increased oxidation current compared to a non-modified surface. The electrochemical activity of this sensor can be easily tuned. Glucose is a standard compound for evaluating the chemical oxygen demand (COD), and we have therefore studied the application of the sensor to the determination of this parameter. Under optimized conditions, the sensor has linear response to glucose in the 1.92-768 mg L concentration range, and the detection limit is 0.609 mg L (at an S/N ratio of 3). A large number of surface water samples was studied, and the results obtained by this method were found to be linearly correlated to those obtained by the dichromate method (r = 0.995; n = 33). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Copyright of Chemical Industry / Hemijska Industrija is the property of Association of Chemical Engineers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: [•] A recombinant laccase with Cys-6×His tag at the N or C terminus was generated. [•] Orientation controlled laccase electrodes were constructed via self assembly. [•] The electrochemical behavior of laccase electrodes was orientation dependent. [•] The C terminus tagged laccase was better for bioelectrocatalytic reduction of O2. [ABSTRACT FROM AUTHOR]

Abstract: The electrochemical behavior of ethanethiol was studied on polycrystalline gold electrodes in alkaline solution. With the help of cyclic voltammetry, differential pulse voltammetry and ex-situ X-ray photoelectron spectroscopy it is possible to propose a coherent reaction mechanism. Under the experimental condition gold thiolate and “gold hydroxide” are formed at the respective potentials. Dissolved and surface confined thiolate can be oxidized to the corresponding dithiol. The “gold hydroxide” reduction is accompanied by gold thiolate formation; the latter being stable at more negative potentials than the gold hydroxide. The experimental results indicate that thiolate ions react with the “gold hydroxide” layer by formation of a gold–thiolate layer and release of hydroxide ions to the solution. This non-electrochemical reaction is confined to the potential range where the gold–thiolate layer is stable. [Copyright &y& Elsevier]

The electrochemical properties of Au electrodes grafted with 4-nitrophenyl and 4-decylphenyl groups have been studied. The electrografting of gold electrode surface with aryl groups was carried out by electroreduction of the corresponding diazonium salts in acetonitrile. The nitrophenyl film growth on gold was examined by atomic force microscopy, electrochemical quartz crystal microbalance and X-ray photoelectron spectroscopy. These measurements showed that a multilayer film of nitrophenyl groups was formed. Cyclic voltammetry was used to study the blocking properties of aryl-modified gold electrodes towards the Fe(CN) redox system. The reduction of oxygen was strongly suppressed on these electrodes as evidenced by the rotating disc electrode results. [ABSTRACT FROM AUTHOR]

Abstract: A simple and sensitive electrochemical immunosensor for the detection of protein biomarker interleukin-6 (IL-6) based on gold nanoparticles (AuNPs) as label was reported. The signal of the immunosensor was originated from enlarged and positively charged AuNPs mediated electron transfer between insulating self-assemble monolayer (SAM) modified electrode and K3Fe(CN)6 solution. The gold electrode was first modified with SAM to block the electron transfer between the electrode and K3Fe(CN)6 solution. After the preparation of the immunosensor, the AuNPs attached onto electrode was enlarged and positively charged when treated in solution containing HAuCl4, ascorbic acid and cetyltrimethylammonium bromide (CTAB). The enlarged and positively charged AuNPs then mediated electron transfer between the electrode and K3Fe(CN)6 solution, creating redox current that is proportional to the concentration of IL-6 detected. The reported immunosensor has high sensitivity and wide linear range. This novel signal amplification strategy can be applied to the detection of different kinds of protein biomarkers. [Copyright &y& Elsevier]

Abstract: Electrochemical electrodes incorporating double- and single-walled carbon nanotubes (CNTs) were fabricated on cysteamine modified flat gold substrates. Through covalent coupling of the amine end groups with carboxyl functionalized CNTs, a dense forest of vertically aligned CNTs was produced. To these a 30nm thick insulating polystyrene layer was spin coated, resulting in exposure of the uppermost carbon nanotube ends. The electrochemical performance of each electrode was then determined using the redox probe ruthenium hexaamine. Once surrounded by polymer, the double-walled CNTs (DWCNTs) showed an improved electron transfer rate, compared to the single-walled electrode. This improvement was attributed to the protection of the electronic properties of the inner wall of the DWCNT during the chemical modification and suggests that DWCNTs may offer a useful alternative to SWCNTs in future electrochemical sensors and biosensors. [Copyright &y& Elsevier]

Abstract: Due to their recognition properties and efficiency for the detection of toxic metals, calixarenes have already found applications in the design of chemical sensors based on using an electrochemical transduction. In this study, a new chromogenic azo-calix[4]arene derivative was deposited on gold electrode by spin coating to develop a new electrochemical sensor. Adhesion and morphological properties of the membrane have been firstly developed using contact angle measurements and scanning electronic microscopy (SEM) respectively. Electrochemical impedance spectroscopy (EIS) is used to study the response of the calixarenes membrane in contact with aqueous solutions of various metallic cations. The impedance behavior of the structures has been modeled by an equivalent circuit using the Z-View software. This technique has shown a selective response of this membrane towards Hg2+, Ni2+ and Eu3+. The differences in selectivity are found to be represented by variations in the resistance of the membrane (R m) and in the charge transfer resistance (R ct) of the interface. Variation of CPE1 and CPE2 have been also investigated which were correlated to the porosity of the film and the exchange of the charge between the substrate and the electrolyte respectively. [Copyright &y& Elsevier]

The electrochemical behaviors of thiazolidine (tetrahydrothiazole) on gold and platinum electrodes were investigated in a Britton-Robinson buffer (pH 2.77-11.61), acetate buffer (pH 4.31), phosphate buffer solutions (pH 2.11 and 6.38) and methanol or acetonitrile containing various supporting electrolytes. Detection was based on a gold wire electrochemical signal obtained with a supporting electrolyte containing 20% methanol-1.0 mM of phosphate buffer (pH 6.87, potassium dihydrogen phosphate and dipotassium hydrogen phosphate) as the mobile phase. Comparison with results obtained with a commercial amperometric detector shows good agreement. Using the chronoamperometric sensor with the current at a constant potential, and measurements with suitable experimental parameters, a linear concentration from 0.05 to 16 mg L-1 was found. The limit of quantification (LOQ) of the method for thiazolidine was found to be 1 ng. [ABSTRACT FROM AUTHOR]

Abstract: A 4-amino-6-hydroxy-2-mercaptopyrimidine monohydrate (AHMP)-based self-assembled monolayer (SAM) was formed on the gold electrode surface. Ellipsometric measurements evidenced the SAM formation on the gold electrode surface. The structural integrity of the modified gold electrode was also characterized by insulating properties of the SAM that were detected by cyclic voltammetry. The results of cyclic voltammetry showed that the SAM, which was formed by assembly of AHMP, was stable but did not completely block the redox-activity of ferrocene and K3[Fe(CN)6]/K4[Fe(CN)6]. In contrast completely blocked redox-activity was observed after the treatment of AHMP-based SAM with saturated solution of 4-formylphenylboronic acid in 1,4-dioxan. The modified electrodes exhibited a selective response towards Cu(II) ions in the presence of some interfering ions such as Cd(II), Co(II), Fe(II), Ni(II) and Pb(II). This study is the first scientific report on the application of AHMP-modified electrode as a selective Cu(II) sensor in the presence of some interfering cations. [Copyright &y& Elsevier]

Abstract: A disposable electrochemical immunosensor has been developed for the determination of phenyl urea herbicide-diuron using a low cost laser ablated gold electrodes (LC-LAGE) fabricated on polystyrene substrate. The electrodes were electrochemically deposited with prussian blue-gold nanoparticle (PB-GNP) film, and a competitive inhibition immunoassay was performed on LC-LAGE by using a specific hapten–protein conjugate. The binding of available diuron specific antibody on conjugate coated electrode was detected using alkaline phosphatase rabbit anti-IgG antibody. The addition of 1-naphthyl phosphate substrate resulted in the production of electrochemically active product, 1-naphthol, which was monitored using square wave voltammetry technique. The assay exhibited an excellent sensitivity and specificity showing the dynamic response range between 1ppt and 10ppm for diuron with detection limit around 1ppt. This study provides insight into development of a rapid and high-throughput screening of pesticides in environmental samples at a very low cost. [Copyright &y& Elsevier]

Abstract: The present article describes the development of a microfluidic-enzymatic sensor with electrochemical detection for the quantification of pipemidic acid (PA), which is a synthetic quinolone used as antibacterial agent. This property of the quinolones is associated with their potential to inhibit topoisomerase II (DNA gyrase) of bacteria. PA detection in pharmaceutical samples was based in the use of tyrosinase enzyme [EC 1.14.18.1] that was immobilized on 3-aminopropyl-modified-controlled-pore glass (APCPG) packet in a central channel (CC) of the microfluidic-enzymatic device. This enzyme catalyzes the oxidation of catechol to o-benzoquinone, whose back electrochemical reduction was detected at gold electrode surface at 0V vs. Ag/AgCl. Thus, when PA was added to the solution, this piperazine-containing compound participates in a Michael addition reaction with o-benzoquinone to form the corresponding amino-quinone derivative, as result of this interaction the peak current obtained for o-benzoquinone reduction decreased proportionally to the increase of the PA concentration. The recovery of PA from four samples ranged from 97.50% to 102.50%. This method could be used to determine the PA concentration in the range 0.02–70μM (r =0.998) with a limit of detection of 18nM. This method was successfully applied for the analysis of PA in pharmaceutical formulations. [ABSTRACT FROM AUTHOR]

Abstract: Laccases and other multicopper oxidases are reported to be able to carry out direct electron transfer reactions when immobilized onto electrode surface. This allows detailed research of their electron transfer mechanisms. We have recently characterized the kinetic properties of four laccases in homogenous solution and immobilized onto an electrode surface with respect to a set of different redox mediators. In this paper we report the direct electron transfer of four purified laccases from Trametes hirsuta (ThL), Trametes versicolor (TvL), Melanocarpus albomyces (r-MaL) and Rhus vernicifera (RvL), by trapping the proteins within an electrochemically inert polymer of tributylmethyl phosphonium chloride coating a gold electrode surface. In particular, we have characterized the steps involved in the laccases electron transfer mechanism as well as the factors limiting each step. During the voltammetric experiments, non-turnover Faradic signals with midpoint potential of about 790 and 400mV were observed for high potential laccases, ThL and TvL, corresponding to redox transformations of the T1 site and the T2/T3 cluster of the enzyme, respectively, whereas low redox potential laccases r-MaL and RvL shown a redox couple with a midpoint potential around 400mV. The electrocatalytic properties of these laccase modified electrodes for the reduction of oxygen have been evaluated demonstrating significative direct electron transfer kinetics. The biocatalytic activity of laccases was also monitored in the presence of a well known inhibitor, sodium azide. On the basis of the experimental results, a hypothesis about the electronic pathway for intramolecular electron transfer characterizing laccases has been proposed. [ABSTRACT FROM AUTHOR]