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In the past decades, many efforts have been made to improve the sensitivity and specificity of electrochemical DNA biosensors. However, it is still strongly required to develop disposable and reliable DNA biosensors for wide and practical application. In this article, we reported superior electrochemical properties of an integrated plastic-gold electrode (PGE) fabricated in-house by chemical plating on polystyrene substrate. PGEs were found having extremely high capacity of DNA immobilization compared with gold electrodes fabricated by standard sputtering based photolithography. Unique nano-structured surface was observed on PGEs through morphology techniques, which would to some extend give an explanation to higher capacity of DNA immobilization on PGEs. A probable mechanism of carboxylic acid produced on polystyrene substrate after exposure to UV irradiation was proposed and discussed for the first time. This biosensor was applied to detection and manipulate of DNA hybridization. Detection limit of 7.2×10 −11 M and 1–500 nM of linearity range was obtained. [ABSTRACT FROM AUTHOR]

The free metal ion concentration and the dynamic features of the metal species are recognized as key to predict metal bioavailability and toxicity to aquatic organisms. Quantification of the former is, however, still challenging. In this paper, it is shown for the first time that the concentration of free copper (Cu 2+ ) can be quantified by applying AGNES (Absence of Gradients and Nernstian equilibrium stripping) at a solid gold electrode. It was found that: i) the amount of deposited Cu follows a Nernstian relationship with the applied deposition potential, and ii) the stripping signal is linearly related with the free metal ion concentration. The performance of AGNES at the vibrating gold microwire electrode (VGME) was assessed for two labile systems: Cu-malonic acid and Cu-iminodiacetic acid at ionic strength 0.01 M and a range of pH values from 4.0 to 6.0. The free Cu concentrations and conditional stability constants obtained by AGNES were in good agreement with stripping scanned voltammetry and thermodynamic theoretical predictions obtained by Visual MinteQ. This work highlights the suitability of gold electrodes for the quantification of free metal ion concentrations by AGNES. It also strongly suggests that other solid electrodes may be well appropriate for such task. This new application of AGNES is a first step towards a range of applications for a number of metals in speciation, toxicological and environmental studies for the direct determination of the key parameter that is the free metal ion concentration. [ABSTRACT FROM AUTHOR]

The electroanalytical characterization and determination of three selected β-blocker agents, namely propranolol, atenolol and nadolol using cyclic voltammetry and differential pulse voltammetry (DPV) in phosphate buffer solution (pH 2.5) plus 22 % acetonitrile (ACN), was described. The analytes were characterized through their electrooxidation processes on polycrystalline gold electrodes. The analytical determination of the selected molecules was performed using the differential pulse voltammetry (DPV) at pH 2.5. Under DPV conditions, the detection limits (LODs) ranged between 5 μM and 20 μM for propranolol and atenolol, respectively. For all investigated molecules, two well-defined ranges of linearity Ip vs analyte concentration have been identified which correspond to specific calibration parameters. Calibration graphs (Ip vs concentration) considered in the first interval of linearity, shown correlation coefficients >0.99. A solid phase extraction (SPE) procedure using a polymeric mixed-mode cationic sorbent (Strata-X-C), was studied and optimized. The proposed DPV-SPE method was successfully applied for the determination of propranolol in several pharmaceutical formulations and urine sample, with results in close agreement with those obtained using traditional liquid chromatography technique coupled with spectrophotometric detection. [ABSTRACT FROM AUTHOR]

Overpotential for oxygen reduction reaction (ORR) at Au electrode is reported to be reduced by 0.27 V by the modification with boron nitride nanosheet (BNNS) but oxygen is reduced only to H 2 O 2 by 2-electron process at Au electrode. Here we demonstrate that the decoration of BNNS with gold nanoparticles (AuNP) not only reduces the overpotential for ORR further by ca. 50 mV, but also opens a 4-electron reduction route to water. Both rotating disk electrode experiments with Koutecky–Levich analysis and rotating ring disk electrode measurements show that more than 50% of oxygen is reduced to water via 4-electron process at Au–BNNS/Au electrode while less than 20 and 10% of oxygen are reduced to water at the BNNS/Au and bare Au electrodes, respectively. Theoretical analysis of free energy profiles for ORR at the BN monolayer with and without Au 8 cluster placed on Au(111) shows significant stabilization of adsorbed oxygen atom by the Au 8 cluster, opening a 4-electron reduction pathway. [ABSTRACT FROM AUTHOR]

Tebuconazole, a pesticide that presents risks for ecosystems, groundwater and human health, was degraded on a gold electrode as the catalyst in 0.05 M NaHCO 3 using cyclic voltammetry (CV). First, tebuconazole was characterized on the gold electrode using CV and square wave voltammetry (SWV). The gold electrode, being highly sensitive, provided linear relationships (currents vs . concentrations) in the range: (0.076–0.76 μmol dm –3 ). Based on the CV measurements, the investigated process is irreversible and diffusion-controlled. The observed catalytic role of the Au electrode in the oxidation of tebuconazole and the data obtained from CV and SWV provided the experimental conditions for the degradation of tebuconazole. The degradation was performed by continuous cycling followed by gas chromatography–mass spectroscopy (GC–MS) analysis. This enabled the catalytic elimination of tebuconazole for 60 min, which promoted the use of a gold electrode as the catalyst for the degradation of environmental pollutants. The scheme of the possible mechanism of tebuconazole degradation is given. [ABSTRACT FROM AUTHOR]

In this work a gold electrode modified with self-assembled layers (SAMs) composed with organic S-containing compound and gold nanoparticles was prepared. The electrode with SAMs endowed with gold nanoparticles gave the high catalytic effect for ethylene glycol (EG) electrooxidation in solution at pH 7. For this novel sensor a linear relationship between the current response of EG at the potential of peak maximum ( jp) and the concentration of this compound in solution ( cEG) was found over the range 0.1 µM to 0.7 M with the detection sensitivity jp/ cEG equal to about 5 A cm−2 mol−1 dm3 (at v=0.1 V s−1) and the detection limit of 0.046 µM. [ABSTRACT FROM AUTHOR]

In this study, a new Schiff base of bis-N-(2-mercaptophenyl) salicylaldimine (MPSI) has been immobilized on a bare gold electrode as a novel self assembled monolayer (SAM) sensor for determination of promethazine hydrochloride (PMZ). Cyclic voltammetry and electrochemical impedance spectroscopy are used to study the properties of monolayer of Schiff's base on a gold electrode (MPSI-Au SAM electrode) using the [Fe(CN) 6 ] 3 −/4 − probe. Also, the characterization of the MPSI-Au electrode was performed by scanning electron (SEM) and atomic force microscopy (AFM). The electrochemical behavior of PMZ on the MPSI-Au SAM electrode was studied by several voltammetry methods in phosphate buffer solution as supporting electrolyte. The modified electrode showed good selectivity in the presence of interference of ascorbic and uric acid. A calibration curve was obtained for PMZ in a linear range of 1.0–240.0 μmol L − 1 . The detection limit for promethazine hydrochloride was found to be 24.6 nmol L − 1 . The results indicated that the MPSI-Au SAM electrode could be employed for the determination of promethazine hydrochloride in urine and plasma samples. [ABSTRACT FROM AUTHOR]

The authors describe a highly sensitive platform for the determination of uranyl ion (UO) that is based on the integration of an UO-specific DNAzyme and a target-catalyzed hairpin assembly. Each DNAzyme consists of an enzyme strand (E-DNA) and a substrate strand (S-DNA). The S-DNA is selectively cleaved in the presence of UO. The released fragment of S-DNA hybridizes with hairpin probe 1 (H1) immobilized on a gold electrode. This is accompanied by unfolding of H1 which induces the hybridization with hairpin 2 (H2). The DNA fragment spontaneously dissociates from the surface and then initiates the next hybridization cycle. After multiple cycling, the electrochemical probe Methylene Blue (MB) is added to intercalate into the minor grooves of the dsDNA. The combination of signal amplification and the use of a highly specific DNAzyme results in a highly sensitive sensor for UO. At a typical working voltage of −0.22 V (vs Ag/AgCl), a linear response is found range for the 10 pM to 1 nM concentration range, and the detection limit is as low as 2 pM. This strategy provides a powerful and generally applicable tool that may be extended to other metal ions for which specific DNAzymes and signal probes are available. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

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]

Herein, a simple and effective electrochemical biosensor for sensitive detection of acrylamide (AA) was developed by differential pulse voltammetry (DPV) approach. This biosensor was prepared by effective self-assembling process of thiol group functionalized single-stranded DNA (ssDNA) on the surface of gold electrode (GE) through specific Au S covalent bond. The ssDNA/GE showed a single strong DPV oxidation peak, which was used as the electrochemical signal for AA sensing. The bonding interaction between AA and ssDNA was confirmed by UV–vis absorption spectrometry and DPV. AA and ssDNA formed a single complex and the binding ratio of AA with ssDNA was one AA per guanine base of ssDNA. The electrochemical oxidation of AA-ssDNA adduct on the surface of GE was an adsorption-controlled irreversible reaction and a two-electron two-proton transfer process. Under optimum conditions, ssDNA/GE exhibited excellent DPV response depending on the concentration of AA in 0.4–200 μM range. The limit of detection was 8.1 nM (3 σ /slope). This electrochemical biosensor displayed good reproducibility and high stability. This biosensor was successfully applied to the determination of AA in tap water and potato crisps. This electrochemical platform is convenient and efficient, offering great potential for construction of electrochemical biosensors toward various toxic substances. [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]

Facile and efficient template synthesis of new manganese(II) complex [Mn 2 (H 2 L ) 2 ](ClO 4 ) 2 ( 1 ) and its crystal structure are reported. Self-assembly leads to the formation of dinuclear, phenoxo-bridged closed species via exploitation of both binding subunits of the in situ formed new Schiff-base ligand. Gold electrode modified with self-assembled monolayers (SAMs) composed of synthesized complex 1 was applied as a voltammetric sensor for quantitative determination of dopamine (DA) in the presence of ascorbic (AA) and uric acids (UA). The linear relationship between the current response of dopamine at the potential of peak maximum and the concentration was found over a wide analyte concentration range ( R 2 ≥0.993, 1×10 −10 –8.5×10 −4 M) with a very good sensitivity (4.11 A cm −2 M −1 at d E /d t =0.1 V s −1 ), high detection limit (6.8×10 −9 M) and excellent reproducibility. It has been proven that current peaks of dopamine, ascorbic and uric acids were clearly separated from each other, thus enabling selective detection of these compounds coexisting in a mixture. [ABSTRACT FROM AUTHOR]

The electro reductive behavior and determination of bromate on [5, 10, 15, 20-tetrakis (4-methoxyphenylporphyrinato] Manganese (III) chloride (TMOPPMn(III)Cl) modified Gold electrode(GE) was investigated by Square wave voltammetry (SWV). Bromate showed an irreversible reduction peak at −164 mV in 0.1 M pH 7 NaSO solution. The cathodic peak of bromate showed a reduction in potential of 88 mV on modifying GE with a porphyrin film. The peak current varied linearly with concentration with a detection limit of 3.56 × 10 M. The influence of pH, scan rate, supporting electrolyte and interferents on the reduction peak current of bromate were studied. The developed sensor was proposed for the determination of bromate in bread samples and compared with the standard method. [ABSTRACT FROM AUTHOR]

Electrochemical oxidation of sulfite ions on gold was studied by means of voltammetry with the electrode renewed by cutting off a thin layer. It was demonstrated that two different kinds of voltammograms can be recorded on gold, depending on experimental conditions. Voltammograms of the first kind, with current maximum at 0.8 V, is typical for the fresh gold surface. The second one, with current maximum at 0.6 V, is observed on gold surface modified during sulfite oxidation. Modification of gold surface is likely to be due to the formation of “sulfur adlayer” in the reduction of adsorbed products of sulfite oxidation. Attention is attracted to the fact that the characteristics of the oxidation of sulfite and sulfur dioxide on gold have many common features. [ABSTRACT FROM AUTHOR]

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 K 4 [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. [ABSTRACT FROM AUTHOR]

Melamine is an organic base and a triazine of cyanamide with a 1,3,5-triazine skeleton. It contains 67% a nitrogen by mass. It is introduced as a contaminant in food products with the intent to falsify total protein content. The illegal adulteration of infant milk powder with melamine has resulted in chronic kidney and urinary tract failure. To date, several analytical methods have been developed for the detection of melamine. However, the existing methods are complicated, time consuming and costly. There is an urgent need to develop a simple, fast and effective method for the analysis of melamine in infant milk and milk products. For that reason, an novel electrochemical method was developed based on an ionic liquids (1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Otf])), zinc oxide nanoparticles (ZnONPs) with chitosan (CHIT), and the modified gold electrode (AuE). Methylene blue was used as a redox indicator for increasing the electron transfer in electrochemical cell. The electrochemical behaviour of the modified gold electrode was studied by using cyclic voltammetry and differential pulse voltammetry at the presence of melamine. The morphological characteristics were observed under scanning electron microscope and transmission electron microscope. The electrochemical sensor showed an optimal response within 30 s, pH 7.0 and 0.3 V. Under optimal conditions, differential pulse voltammetry was detected a wide linear range of melamine concentrations from 9.6 × 10 −4 to 9.6 × 10 −13 M, with a detection limit 9.6 × 10 −14 M. The linear regression equation for the calibration plot was calculated to be y = 0.4239x + 6.6686 (r 2 = 0.9836), where x is the concentration of melamine and y is the oxidation current. The proposed method is fast and simple procedure technique for analysing the melamine level in milk powder products. [ABSTRACT FROM AUTHOR]

In this work, a gold electrode modified with self-assembled layers (SAMs) composed of 3-mercaptopropionic acid, cysteamine and gold nanoparticles was prepared. The electrode with SAMs endowed with gold nanoparticles gave the high catalytic effect for monoethanolamine (MEA) electrooxidation in solution at pH 7. For this novel sensor, a linear relationship between the current response of MEA at the potential of peak maximum ( j) and the concentration of this compound in solution ( c) was found, over the range 0.1 μM to 0.8 M with the detection sensitivity equal to about 5 A cm mol dm (at v = 0.1 V s) and the detection limit of 0.046 μM . [ABSTRACT FROM AUTHOR]

Canonical Monte Carlo simulations, at 298 K, of the adsorption of phenol in a dilute aqueous solution on gold electrodes, at the potential of zero charge, are presented. The results suggest that the process occurs in two distinct and successive steps. Adsorption starts with the phenol oxygen atom pointing towards the gold surface and the aromatic ring in a quasi-perpendicular orientation relative to the surface. This is followed by the reorientation of the aromatic ring to a parallel configuration. The effect of the solvent is analyzed through the calculation of the potential of mean force acting on phenol. Despite the simplicity of the model and the interaction potentials used in the simulations, the results are in good agreement with experimental observations, giving insight into the microscopic details of the adsorption process of phenol at low concentrations.

The voltammetric behavior of prochlorperazine and ethopropazine at a decanethiol (DEC) self-assembled monolayer (SAM) modified gold electrode (DEC/Au) has been studied. It was observed that prochlorperazine exhibited an anodic peak at about 0.60 V (vs SCE), while ethopropazine exhibited two anodic peaks at about 0.49 V and 0.58 V on DEC/Au in pH 10 sodium carbonate buffer. This was due to their different electrochemical oxidation mechanisms. In this case, the oxidation of prochlorperazine and ethopropazine included one 2e step and two 1e steps, respectively. In the presence of some reductants such as ascorbic acid, the oxidation products of them can catalyze the oxidation of the reductants and thus make the peaks grow. In addition, it was found that the SAM structure became not so compact when prochlorperazine and ethopropazine were present, resulting from their permeating in the SAM. Various conditions were optimized for their determination. Under the selected conditions (i.e. 0.080 M pH 10 sodium carbonate buffer; scan rate: 100 mV/s; accumulation potential: –0.4 V or 0 V; accumulation time: 60 s), the peak currents were linear to prochlorperazine concentration in the ranges of 0.1~2.0 μM and 5.0~50 μM, and linear with ethopropazine in the ranges of 10 nM~0.1 μM and 0.5~20 μM. The RSD was 4.28% for 8 successive measurements of 1.0 μM prochlorperazine. The influence of some coexistents was examined.

[Display omitted] • Cr(VI) voltammetric determination in acidic medium using a gold electrode. • Eco-friendly alternative for the stainless steel sample preparation. • Fast and low-cost process for dissolving metal alloys. • Steel dissolution and Cr(VI) voltammetric determination in the same electrolyte. In this work, a fast, simple and eco-friendly method using electrolytic dissolution and linear sweep voltammetry to quantify chromium in stainless steel samples in just two steps was developed. The electrolytic dissolution was performed in 0.6 mol/L HNO 3 solution, applying 0.8 mA cm−2 current density and 30 mC electrical charge, without gas evolution at the electrodes and anodic passivation tendency. In the same electrochemical cell and electrolyte, the voltammetric measurement was performed using a gold electrode to monitor the reduction current of Cr(VI) ions. The method presented excellent analytical performance with a limit of detection of 0.08 µmol/L, a wide working linear range from 0.3 to 2.1 µmol/L (15.6 to 109.2 µg/L), and good precision (RSD = 3%, n = 10). The results obtained are evidence that the developed method has good accuracy since the chromium concentrations are in agreement with the reference values at a 95% confidence level. Additionally, this method was extremely fast, requiring only 75 s for dissolution and voltammetric measurement, making it a promising analytical tool for implementation in quality control analyses of stainless steel manufacturing. [ABSTRACT FROM AUTHOR]

[Display omitted] • Good electrochemical responses due to biocide oxidation on gold electrode. • The first HPLC-ECD method with gold electrode for biocide determination. • Good analytical features to control the amount of antimicrobial agents in cosmetics. • Successful results in cosmetic analysis with the HPLC-ECD method. Antimicrobial agents are added to a wide variety of products such as cosmetics to reduce the risk of microbial contamination and ensure the suitability and safety of the product. However, recent studies have shown that these compounds can have negative effects on human health and the environment. Therefore, it is crucial to develop analytical methods to control the amount of these compounds in personal care products to guarantee human health and product quality. This paper presents an HPLC method with electrochemical detection using a gold electrode for the determination of the most used antimicrobial agents in cosmetic products: methylparaben (MP), 4-hydroxybenzoic acid (4-HBA), phenoxyethanol (PE) and methylisothiazolinone (MIT). For this purpose, the electrochemical response of these compounds was evaluated on the gold electrode. The optimal electrochemical detection of MP, 4-HBA; PE and MIT was performed at pH 2 and + 1.50 V (vs Ag/AgCl). Under the optimal separation and detection conditions, limits of detection (LODs) between 10 and 110 μg L−1 were obtained. These LODs are lower than those previously reported for other HPLC methods with mass spectrometry and diode-array detectors. Cosmetic products with different compositions were successfully analysed with the proposed HPLC method obtaining recoveries between 76 % and 119 %. [ABSTRACT FROM AUTHOR]

Cocaine is a strong central nervous system stimulant and one of the most commonly abused drugs. In this study, an electrochemical aptasensor was designed for sensitive and selective detection of cocaine, based on single-walled carbon nanotubes (SWNTs), gold electrode and complimentary strand of aptamer (CS). This electrochemical aptasensor inherits properties of SWNTs and gold such as large surface area and high electrochemical conductivity, as well as high affinity and selectivity of aptamer toward its target and the stronger interaction of SWNTs with single-stranded DNA (ssDNA) than double-stranded DNA (dsDNA). In the absence of cocaine, a little amount of SWNTs bind to Aptamer-CS-modified electrode, so that the electrochemical signal is weak. In the presence of cocaine, aptamer binds to cocaine, leaves the surface of electrode. So that, a large amount of SWNTs bind to CS-modified electrode, generating to a strong electrochemical signal. The designed electrochemical aptasensor showed good selectivity toward cocaine with a limit of detection (LOD) as low as 105 pM. Moreover, the fabricated electrochemical aptasensor was successfully applied to detect cocaine in serum with a LOD as low as 136 pM. [ABSTRACT FROM AUTHOR]

Gold versus Platinum Ablation Electrodes Introduction During radiofrequency (RF) catheter ablation, convective cooling of the ablated tissue by circulating blood allows higher power delivery and deeper penetration of volume heating without excess surface heating. The study aim was to characterize ablation lesions using electrode materials with differing thermal conductivities and magnitudes of passive convective cooling utilizing duty-cycled RF energy. Methods and Results RF ablations using a linear array of 4 3-mm platinum electrodes (n = 228) were compared to an array with gold electrodes (n = 244). RF was delivered using temperature feedback power control, in a blended bipolar:unipolar mode (2:1 and 4:1), to exposed porcine thigh muscle superfused with heparinized blood. For gold electrodes, lesion depths were 4.1 ± 0.8 mm in the 2:1 ablation mode and 3.7 ± 0.9 mm in the 4:1 ablation mode, versus 3.7 ± 1.0 mm and 3.3 ± 1.0 mm with platinum (P < 0.001 vs. gold, P = 0.004 platinum 2:1 vs. 4:1). More efficient passive cooling at all flow rates with gold versus platinum resulted in a lower mean electrode temperature and a higher proportion of ablations reaching maximum power before achieving target temperature. Therefore, the mean ablation power was higher with gold (6.5+2.1 vs. 5.5+2.3 W, P < 0.001), and lesion depth was greater (3.9+0.8 mm vs. 3.5+1.0 mm, P < 0.001) compared to platinum. Conclusions Passive convective cooling during RF ablation is more efficient with gold compared to platinum electrodes, particularly when ablations are temperature limited. Using temperature feedback power control, deeper lesions can be reliably achieved with gold electrodes. [ABSTRACT FROM AUTHOR]

In this work, a gold electrode (GE) was modified by coating with two dimensional silica network/citrate capped gold nanoparticles–poly(diallyldimethylammonium chloride) (GE–TDSN–CGNP–PDDA) for ultra-sensitive determination of Bovine Serum Albumin (BSA). After covalently binding of a silica network (in two-dimensional form) on the surface of a gold electrode, via twice in situ hydrolysis of 3-mercaptopropyl-tri-ethoxysilane, citrate capped gold nanoparticles (CGNP) were chemically adsorbed on the silica cage. Subsequently, PDDA was bonded to CGNP via electrostatic interaction of positively charged polymer and negatively charged stabilizer of CGNP. Analytical properties of GE–TDSN–CGNP–PDDA were studied by Electrochemical Impedance Spectroscopy (EIS). The detection limit for measured BSA was found to be 8.4×10 − 13 mol L − 1 and the measuring linear concentration range of the proposed sensor was 9.9×10 −12 –1.6×10 −10 mol L − 1 of BSA. In addition, GE–TDSN–CGNP–PDDA exhibited good stability with high selectivity and was applied for determination of BSA in some samples with satisfactory results. [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]

A sensitive voltammetric method for the determination of tert-butylhydroquinone (TBHQ), a widely used synthetic phenolic antioxidant in oils and fats, using multiwalled carbon nanotube modified gold electrode (MWCNT/GE) was developed. In 0.10 M phosphate buffer solution (PBS) of pH 2, TBHQ gave redox peaks at E = 258 mV and E = 228 mV on MWCNT/GE. Diffusion-controlled electrooxidation of TBHQ was found to be perfectly reversible with the involvement of two electrons and two protons. The anodic peak currents varied linearly with concentrations of TBHQ in the range 4.0 × 10 to 1.00 × 10 M. The limit of detection achieved for the developed sensor was 3.20 × 10 M (5.31 ng mL). Developed sensor was used for the determination of TBHQ in commercially available coconut oil. The results obtained from the developed method were in good agreement with the standard method (HPLC-UV). [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]

Airborne particulate matter (PM) contains several quinones, which are able to generate reactive oxygen species impacting on cell viability. A method able to detect and quantify PM oxidative potential, based on the cytochrome c (cyt-c) reduction by means of superoxide anion produced through quinones redox cycling in the presence of reducing agents, is here described. Tris(2-carboxyethyl)phosphine resulted to be the most efficient reducing agent among the ones tested. The procedure included rapid particles extraction, followed by two alternative analytical methods, a spectrophotometric assay based on the initial rate of cyt-c reduction at 550 nm, and an amperometric assay, based on self-assembled monolayers modified gold electrodes. The smallest amount of PM needed to obtain an evaluable signal is 2 μg. The described procedure may represent a starting point to develop devices for PM measurements in polluted atmospheric environments. [ABSTRACT FROM AUTHOR]

We investigated an insulin-sensing method by utilizing an insulin-binding aptamer IGA3, which forms an anti-parallel G-quadruplex with folded single strands. Spectroscopic observation indicates that some anti-parallel G-quadruplex bind hemin and show peroxidase activity. In this study, the peroxidase activity of IGA3 with hemin was confirmed by spectrophotometric measurements, i.e., the activity was three-times higher than hemin itself. IGA3 was then immobilized onto a gold electrode to determine its electrochemical activity. The peroxidase activity of the immobilized IGA3-hemin complex was determined by cyclic voltammetry, and a cathodic peak current of the electrode showed a dependence on the concentration of H2O2. The cathodic peak current of the IGA3-hemin complex decreased by binding it to insulin, and this decrease depended on the concentration of insulin. [ABSTRACT FROM AUTHOR]

A wide range of chromatographic methods for the analysis of phenolic compounds in medicinal plants has been published over the years. However, no chromatographic methods with pulsed amperometric detection using a gold electrode have been described to analyze phenolic acids and flavonoids. Moreover, there is a lack of information regarding a modified mobile phase with β-cyclodextrin to determine these compounds in plants by RP-HPLC. For this reason, the present study developed and validated an HPLC–PAD method to determine 12 phenolic compounds in medicinal plants from Amazonia. The isocratic mobile phase was constituted by sodium phosphate 50 m mol L−1, methanol 30% (v/v), and β-cyclodextrin 1 m mol L−1at pH 2.0. The method demonstrated low detection and quantification limits and robustness. The accuracy ranged from 82–114% for chlorogenic acid and rutin, respectively. Six species of medicinal plants from Amazonia used for medicinal and nutritional purposes were characterized and showed the presence of at least one of the phenolic compounds in the study. [ABSTRACT FROM AUTHOR]

Tuberculosis (TB), an infectious disease affects millions of humans worldwide and is caused by the Mycobacterium tuberculosis . A label free electrochemical DNA biosensor for the detection of M. tuberculosis using gold electrode modified by self-assembled monolayer of thiol is presented in this paper . Single-stranded DNA probe was immobilized on the surface of self-assembled monolayer gold electrode with the assistance of cysteamine and glutaraldehyde, which was further used to hybridize with the target sequence and non-complementary target sequence. Differential Pulse Voltammetry (DPV) was used to characterize the self-assembled monolayer on the gold electrode and also to study the immobilization of ssDNA probe and hybridization with the complementary sequence (target ssDNA). The hybridization reaction on the gold electrode surface was detected by monitoring a guanine oxidation signal at potential +0.21 V. Electrochemical DNA biosensor using gold electrode modified of thiol (Au-SAM) can be used to determine hybridization between ssDNA probe and ssDNA target sequence of M. tuberculosis with sensitvity value is 0.5152; detection limit is 3.47 μg.mL -1 and quantification limit is 11.56 μg.mL -1 [ABSTRACT FROM AUTHOR]

The thiol to disulfide inter-conversion plays vital role in the glutathione (GSH) metabolism in human body. Mimicking the GSH conversion to disulfide by electro-generated reactive oxygen species at gold electrode interface and the use of electro-reduction of the produced disulfides for the electro-analysis of low levels of GSH is reported. [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]

Pyroelectric infrared detectors provide the advantage of both a wide spectral response and dynamic range, which also has enabled systems to be developed with reduced size, weight and power consumption. This paper demonstrates the deposition of lead zirconium titanate (PZT) and lead calcium titanate (PCT) thin films for uncooled pyroelectric detectors with the utilization of gold electrodes. The modified lead titanate thin films were deposited by pulsed laser deposition on gold electrodes. The PZT and PCT thins films deposited and annealed at temperatures of 650 °C and 550 °C respectively demonstrated the best pyroelectric performance in this work. The thin films displayed a pyroelectric effect that increased with temperature. Poling of the thin films was carried out for a fixed time periods and fixed dc bias voltages at elevated temperature in order to increase the pyroelectric coefficient by establishing a spontaneous polarization of the thin films. Poling caused the pyroelectric current to increase one order of magnitude. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The electrooxidation of linear saturated aliphatic alcohols from C1 to C8 on gold in alkaline media has been studied by cyclic voltammetry and with an electrochemical quartz crystal microbalance. The current density of alcohol oxidation very markedly increased and, correspondingly, the onset potential decreased, with increasing chain length, that is, with initially slightly increasing, and then constant, pKa. We attribute this oxidazability increase with chain length to the increasing hydrophobicity of the alcohol. Effectively, a molecular dynamics simulation of the hydration of alcohols and alcoholates shows that the hydrophobicity of the alcohols increases with increasing chain length. The higher activity of gold for the oxidation of organic, and also inorganic (CO), compounds in alkaline media is well known, and should be due to an activation of the gold surface by OH adsorption, and not to a change of the compounds themselves, the (majority) neutral alcohol being the oxidized species both in acid and alkaline media. At the potentials at which 1-heptanol oxidation starts, the mass in both base electrolyte and in 1-heptanol is at a minimum, or nearly so, which shows that water is driven away from the surface of gold prior to the oxidation of both gold and 1-heptanol. [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]

We describe an electrochemical sensor for hydrogen peroxide (HO) that is making use of Prussian Blue (PB) electrodeposited on a macroporous (mp) gold skeleton electrode. An mp-Cu film was first prepared as a template and the converted into an mp-Au film through a replacement reaction without destructing the structure. Next, a layer of PB was electrochemically deposited on the surface of the mp-Au film. The surface morphology of the electrode was characterized by scanning electron microscopy. Attenuated total reflection infrared spectroscopy and X-ray photoelectron spectroscopy were applied to confirm the structural features. The mp-PB/Au film electrode displays high electro-catalytic activity for the reduction of HO at a working potential of −50 mV (vs. Ag/AgCl) and is very stable. It has a linear response to HO in the 50 μM to 11.3 mM concentration range and a sensitivity of 767 μA∙mM cm. The electrode also revealed good selectivity in the presence of electro-active species such as ascorbic acid and uric acid. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The self-assembly of cis-P,P′-dibromo{5,17-dibromo-11,23-bis(diphenylthiophosphine)-25,26,27,28-tetrapropoxycalix[4]arene} (thiacalix[4]arene) containing two sulfur groups in lower rim on gold surfaces is investigated. The thiacalix[4]arene/gold interface is investigated by means of atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The AFM imaging shows the formation of a high density of small pits, a deep gold layer, and a typical feature of self-assembled organosulfur monolayers on gold. CV measurements performed in the presence of [Fe(CN) 6 ] 4−/3− redox couple indicating the passivation of metal electrode, which results in a reduction of redox current after the layer formation. The EIS data were approximated using constant phase element model. The EIS was also used to investigate the selectivity properties of thiacalix[4]arene self-assembled gold electrodes by measuring R ct and total impedance increase in the presence of different salt solutions. It was found that thiacalix[4]arene self-assembled gold electrodes are able to compel cesium ions. The results show good selectivity for cesium ions and a decrease in its detection limit (1.15 × 10 −9 M). [ABSTRACT FROM AUTHOR]

A novel tulathromycin (TLTMC) electrochemical sensor based on molecularly imprinted polymer (MIP) membranes was constructed. p-Aminothiophenol (p-ATP) and TLTMC were assembled on the surface of gold nanoparticles (AuNPs) modified on the gold electrode (GE) by the formation of Au-S bonds and hydrogen-bonding interactions. Besides, polymer membranes were formed by electropolymerization in a polymer solution containing p-ATP, tetrachloroaurate(III) acid (HAuCl), tetrabutylammonium perchlorate (TBAP), and a template molecule TLTMC. A novel molecular imprinted sensor (MIS) in this experiment was achieved after the removal of TLTMC. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) measurements were used to illustrate the process of electropolymerization and its optimal conditions. The electrode with MIP obtained the linear of response range, which was between 3.0 × 10 mol L and 7.0 × 10 mol L, and the limit of detection was 1.0 × 10 mol L. All the obtained results indicate that the MIS tends to be an effective electrochemical technique for the determination of TLTMC in real-time and in a complicated matrix. [Figure not available: see fulltext.] [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]