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Developing electrochemical sensors for ascorbic acid, uric acid and glucose detection provides advantages of rapid, precise and economical monitoring of disease condition, and they have the potential to transform healthcare by enabling point-of-care diagnostic and personalised treatment. Facile and cost-effective potentiometric sensors have been developed in this work for selective and sensitive detection of ascorbic acid, uric acid and glucose, based on molecularly imprinted polymer (MIP). The imprinted polymeric matrix of para-aminobenzoic (pPABA) was developed on the surface of electrochemically reduced graphene oxide modified paraffin impregnated graphite rod electrode (rGO/PIGE). The monomeric para-aminobenzoic acid (PABA) was electropolymerised with template, viz., ascorbic acid, uric acid and glucose individually. The molecularly imprinted electrode surface was created by removing the trapped template molecule. The surface analysis of the modified electrodes was carried out by cyclic voltammetry (CV), scanning electron microscopy (SEM), attenuated total reflection spectroscopy (ATR), Raman spectroscopy and contact angle measurements. Parameters controlling the performance of the MIP (p-PABA), viz., pH of the supporting electrolyte and number of polymerisation cycle, were optimised. Under optimised conditions, the potentiometric responses of MIPs were linearly related to concentrations of ascorbic acid, uric acid and glucose in the range of 3.4 × 10−7 M–2.5 × 10−5 M, 3.3 × 10−7 M–1.3 × 10−5 M, and 3.5 × 10−7 M–2.9 × 10−5 M with a correlation coefficient, R2 of 0.99, 0.99 and 0.98 respectively. All three sensors showed high selectivity even in the presence of high concentration of similar interfering compounds. A limit of detection (LOD) for ascorbic acid, uric acid and glucose was found to be 1.1 × 10−8 M, 2.8 × 10−8 M and 1.3 × 10−8 M respectively. In addition, the developed sensors exhibited long-term stability and good reproducibility. [ABSTRACT FROM AUTHOR]

A native graphene oxide (GO) prepared by Hummers' modified method was used as the template materials for the fabrication of electrochemically oxidative graphene oxide (OGO). The fabrication of OGO onto the glassy carbon electrode (GCE) persuaded via anodic reversible voltammetric cycles of a previously GO-GCE base surface materials. The new adapted approach was simple, cost-effective, and competent for producing active materials by preferential grafting of oxygenated functional groups into the GO lattice. It improved the rate of electron transfer process due to decreasing the contextual stacking among GO layers. The structure, composition, and the reactivity of the prepared OGO were characterized using various analytical techniques. FTIR data signified the richness of OGO surface with oxygenated functionalities including epoxy, ketonic, and carboxylic groups. The SEM images concluded a softer and smoother OGO surface, while the EDS analysis determines the significant differential amount of oxygen in OGO. XPS data confirmed the presence of a new oxygenated peak (not detected in the native GO) assigned to the aldehyde/alcoholic functional group. Cyclic voltammetric (CV) analysis of OGO-GCE in the background electrolyte indicated the existence of a couple reversible redox peaks. Differential pulse voltammetry (DPV) results were evident for the promising efficiency of OGO-GCE on the simultaneous determination of biological and environmental species such as dopamine (DA), ascorbic acid (AA), uric acid (UA), hydroquinone (HQ), and catechol (CC), respectively. [ABSTRACT FROM AUTHOR]

Novel films consisting of nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were fabricated by means of chemical vapor deposition technique and decorated with gold nanoparticles (AuNPs) possessing diameter of 14.0 nm. Electron optical microscopy analysis reveals that decoration of N-MWCNTs with AuNPs does not have any influence on their bamboo-shaped configuration. The electrochemical response of fabricated composite films, further denoted as N-MWCNTs/AuNPs, towards oxidation of dopamine (DA) to dopamine-o-quinone (DAQ) in the presence of ascorbic acid (AA) and uric acid (UA) was probed in real pig serum by means of cyclic voltammetry (CV) and square wave voltammetry (SWV). The findings demonstrate that N-MWCNTs/AuNPs exhibit slightly greater electrochemical response and sensitivity towards DA/DAQ compared to unmodified N-MWCNTs. It is, consequently, obvious that AuNPs improve significantly the electrochemical response and detection ability of N-MWCNTs. The electrochemical response of N-MWCNTs/AuNPs towards DA/DAQ seems to be significantly greater compared to that of conventional electrodes, such as platinum and glassy carbon. The findings reveal that N-MWCNTs/AuNPs could serve as powerful analytical sensor enabling analysis of DA in real serum samples. [ABSTRACT FROM AUTHOR]

We have described the use of a microelectrode to simulate a passivating reaction taking place at a micro or nanoparticle. Reaction at the microelectrode is considered to lead to either diffusion of the product back into solution or the formation of a surface-bound species. A kinetic parameter describes the balance between the two processes. Linear sweep voltammograms were simulated for the first and second scan under different values of the kinetic parameter. These simulations were used to derive an empirical equation relating the change in peak height to the passivation kinetics. The equation was used to examine the oxidation of NADH, phenol and ascorbic acid at a Pt microelectrode, and the oxidation of phenol at alloy microelectrodes of different Pt:Rh content. [ABSTRACT FROM AUTHOR]

In this study, a new amperometric biosensor for creatinine determination was developed. For this purpose, a polypyrrole-polyvinylsulfonate film was prepared by electropolymerization of pyrrole in a polyvinylsulfonate medium on a platinum plate. Creatinase and sarcosine oxidase enzymes were immobilized on polypyrrole-polyvinylsulfonate film by cross-linking with glutaraldehyde. The determination of creatinine was made based on the oxidation of hydrogen peroxide at 0.4 V formed as a result of the enzymatic reaction on the surface of the prepared biosensor. The linear working range of the biosensor obtained was found between 5.0 × 10−6 and 1.0 × 10−4 M. Using this linear graph, the Km (observed) and Imax (observed) values for the double enzyme electrode system were calculated as 5.0 × 10−3 mM and 0.34 µA/min, respectively. Optimum working pH and temperature were determined as 8.0 and 60 °C, respectively. The reusability and shelf life of the biosensor were determined. The effects of interferences in biological environments on biosensor response were investigated. For this purpose, uric acid, ascorbic acid, paracetamol, glycine, urea, and formaldehyde were used. The results have shown that the prepared biosensor has the potential to be used for creatinine determination in biological fluids. [ABSTRACT FROM AUTHOR]

Acetaminophen is a well-known drug commonly used to provide pain relief, but it can also lead to acute liver failure at high concentrations. Therefore, there is considerable interest in monitoring its concentrations. Sensitive and selective acetaminophen electrochemical sensors were designed by cycling a glassy carbon electrode (GCE) to high potentials in the presence of β-CD in a phosphate electrolyte, or by simply activating the GCE electrode in the phosphate solution. Using cyclic voltammetry, adsorption-like voltammograms were recorded. The acetaminophen oxidation product, N-acetyl benzoquinone imine, was protected from hydrolysis, and this was attributed to the adsorption of acetaminophen at the modified GCE. The rate constants for the oxidation of acetaminophen were estimated as 4.3 × 10–3 cm2 s–1 and 3.4 × 10–3 cm2 s–1 for the β-CD-modified and -activated electrodes, respectively. Using differential pulse voltammetry, the limit of detection was calculated as 9.7 × 10–8 M with a linear concentration range extending from 0.1 to 80 μM. Furthermore, good selectivity was achieved in the presence of caffeine, ascorbic acid and aspirin, enabling the determination of acetaminophen in a commercial tablet. Similar electrochemical data were obtained for both the β-CD-modified and activated GCE surfaces, suggesting that the enhanced detection of acetaminophen is connected mainly to the activation and oxidation of the GCE. Using SEM, EDX and FTIR, no evidence was obtained to indicate that the β-CD was electropolymerised at the GCE. [ABSTRACT FROM AUTHOR]

The redox behavior of polyaniline (PANI) doped with polysulfonic acids is studied in slightly acidic and neutral solutions (from pH 4 to pH 7). The dopants used are polystyrene sulfonic acid (PSSA), poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA), and poly-(4,4′-(2,2′-disulfonic acid)-diphenylene-tere-phthalamide) (t-PASA). Thin PANI layers are used in order to identify clearly the redox peak structure. Based on deconvolution of the reductive currents, the pH dependence of the constituent peaks is studied and pathways of the reductive transitions are suggested. With increasing pH, a loss of electroactivity is observed for all three dopants but to a different extent: the largest for PAMPSA- and the smallest PSSA-doped PANIs. In the same time, a stabilization of the conductive emeraldine salt state is observed at pH 7 for all PANIs with the largest extent of stabilization in the PANI/PAMPSA case. The electrocatalytic properties of the polysulfonic acid-doped PANIs are comparatively studied for ascorbic acid (AA) and dopamine (DA) oxidation at pH 7. It is found that all three types of PANI are good electrocatalysts for both reactions with advantage of the PAMPSA-doped layers showing higher absolute oxidative currents for both reactions. The results concerning DA oxidation demonstrate the possibility to involve polysulfonic acid-doped PANIs in electrocatalytic reactions in neutral solutions occurring at high positive potentials beyond the peak potential of the PANI oxidative transition. [ABSTRACT FROM AUTHOR]

Oxidative stress is considered as an imbalance of reactive species over antioxidants, leading to diseases and cell death. Various methods have been developed to determine the antioxidant potential of natural or synthetic compounds based on the ability to scavenge free radicals. However, most of them lack biological relevance. Here, a gold-based self-assembled monolayer (SAM) was compared with a gold-supported lipid bilayer as models for the mammalian cell membrane to evaluate the free radical scavenging activity of different antioxidants. The oxidative damage induced by reactive species was verified by cyclic and differential pulse voltammetry and measured by the increase of electrochemical peak current of a redox probe. Trolox, caffeic acid (CA), epigallocatechin gallate (EGCG), ascorbic acid (AA), and ferulic acid (FA) were used as model antioxidants. The change in the decrease of the electrochemical signal reflecting oxidative membrane damage confirms the expected protective role. Both model systems showed similar efficacies of each antioxidant, the achieved order of radical scavenging potential is as follows: Trolox > CA > EGCG > AA > FA. The results showed that the electrochemical assay with SAM-modified electrodes is a stable and powerful tool to estimate qualitatively the antioxidative activity of a compound with respect to cell membrane protection against biologically relevant reactive species. [ABSTRACT FROM AUTHOR]

Protonation of the molecularly rigid polymer of intrinsic microporosity PIM-EA-TB can be coupled to immobilisation of Fe(CN)63−/4− (as well as immobilisation of Prussian blue) into 1–2 nm diameter channels. The resulting films provide redox-active coatings on glassy carbon electrodes. Uptake, transport, and retention of Fe(CN)63−/4− in the microporous polymer are strongly pH dependent requiring protonation of the PIM-EA-TB (pKA ≈ 4). Both Fe(CN)64− and Fe(CN)63− can be immobilised, but Fe(CN)64− appears to bind tighter to the polymer backbone presumably via bridging protons. Loss of Fe(CN)63−/4− by leaching into the aqueous solution phase becomes significant only at pH > 9 and is likely to be associated with hydroxide anions directly entering the microporous structure to combine with protons. This and the interaction of Fe(CN)63−/4− and protons within the molecularly rigid PIM-EA-TB host are suggested to be responsible for retention and relatively slow leaching processes. Electrocatalysis with immobilised Fe(CN)63−/4− is demonstrated for the oxidation of ascorbic acid. [ABSTRACT FROM AUTHOR]

Remarkable selective analysis of biomolecules i.e., glucose and ascorbic acid on copper oxide facets was reported for the first time. The copper oxide nanostructures were synthesized using different Cu-ions sources i.e., CuCl2 and CuSO4 by utilizing the hydrothermal method, which congregates in flower and hollow sphere morphologies, respectively. Interestingly, the results showed a comparable sensitivity and selectivity of CuO nanostructures toward glucose and ascorbic acid. To provide a deep understanding of the key factors that predominate the efficiency and selectivity of nanostructured CuO toward these biomolecules, density functional theory (DFT) calculations were accomplished. Five different crystal facets including (002), (200), (202), (111), and (110) were considered and their binding energies with the biomolecules were investigated. It was found that the facets with rich Cu or O atoms might control the selectivity toward glucose and ascorbic acid. This approach will be helpful for designing sensitive and selective targeted nanomaterial-based sensors. [ABSTRACT FROM AUTHOR]

Here, a nanoporous gold electrode (NAu) was reported with a unique cone-shape nanohole structure for electrochemical sensing of nitric oxide (NO), which was fabricated via a facile sputtering technique on aluminum oxide membrane. Two kinds of nanoporous gold electrodes fabricated on different aluminum oxide membranes with aperture-size of 20 nm (2020NAu) and 200 nm (2040NAu) were obtained and compared in electrochemically active surface area and electro-oxidation activity. Concerning the determination of NO, it exhibited higher selectivity to NO2− and larger electro-oxidation current on 2020NAu electrode than those on 2040NAu electrode when their backsides were used as sensing interfaces. Meanwhile, the anti-interfering ability of bare 2020NAu electrode was also compared with that on Nafion-modified 2020NAu electrode. Results showed that common electroactive interferents such as H2O2, ascorbic acid, and uric acid could be hindered by cone-shape nanohole structure in the backside of 2020NAu electrode. On the basis of cyclic voltammetry, the linear range was from 4.75 × 10−8 to 9.50 × 10−7 M for NO sensing on 2020NAu electrode. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensor for the simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA), guanine (GUA), and adenine (ADE) was fabricated by the electrochemical deposition of Au nanoparticles onto a horizontal-graphene-modified tantalum wire (Au/HG) electrode. The graphene layer was grown using hot-filament chemical vapor deposition and shows high potential as a novel biosensor. The incorporation of Au nanoparticles and graphene was confirmed by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The electrochemical performance of the electrodes was characterized by electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and cyclic voltammetry (CV). DPV reveals that AA, DA, UA, GUA, and ADE are detected simultaneously using the Au/HG electrode, exhibiting peaks at − 0.101, 0.112, 0.252, 0.608, and 0.874 V, respectively. In a system containing these five analytes, linear calibration plots for AA, DA, UA, GUA, and ADE were obtained over the 4-600, 0.4-20, 0.6-40, 6-500, and 0.6-40 μM ranges, respectively, with corresponding detection limits of 1.76, 0.02, 0.57, 2.5, and 0.42 μM, respectively. The Au/HG layer shows good electrocatalytic activities toward the redox reactions of AA, DA, UA, GUA, and ADE. This sensing electrode exhibited good selectivities, excellent sensitivities, high stabilities, and low detection limits. [ABSTRACT FROM AUTHOR]

In this study, a novel modified glassy carbon electrode with copper polydopamine complex/multiwalled carbon nanotubes (GCE/Cu2+@PDA-MWCNTs) was fabricated and used for voltammetric determination of ascorbic acid (AA), dopamine (DA), acetaminophen (AC), nitrite (Nit), and xanthine (XN). Different techniques such as field emission electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and electrochemical impedance spectroscopy were performed for characterization of the GCE/Cu2+@PDA-MWCNTs. Different electrochemical methods such as cyclic voltammetry, electrochemical impedance spectroscopy and differential pulse voltammetry (DPV) methods were employed to study the behavior of AA, DA, AC, Nit, and XN on this proposed modified electrode. The proposed modified electrode displays intense and indelible electrooxidation response for simultaneous determination of AA, DA, AC, Nit, and XN to five well-separated peaks in the potential range from 0.1 to 1.1 V using CV and DPV methods in phosphate buffer solution with pH 2.0. Under the optimum conditions, the calibration curves were liner up to 175, 125, 75, 150, and 115 μM with detection limits of 0.82, 0.45, 0.87, 0.92, and 0.67 μM for AA, DA, AC, Nit, and XN, respectively. This sensor was used to successfully determine these compounds in human urine and serum samples.ᅟ [ABSTRACT FROM AUTHOR]

Normetanephrine is a marker for pheochromocytoma, a rare catecholamine-secreting and neuroendocrine tumor, that arises from sympathetic and parasympathetic paraganglia. In this work, a novel carbon/chitosan electrode paste was used for sensitive voltammetric determination of normetanephrine and dopamine in the presence of ascorbic acid and uric acid. The modified electrode has shown an increase in the effective area of up to 68%, well-separated oxidation peaks, and an excellent electrocatalytic activity. The electrochemical response characteristics were investigated by cyclic and differential pulse voltammetry. Interestingly, high sensitivity and selectivity in the linear range of normetanephrine, dopamine, ascorbic acid, and uric acid concentrations were observed. The present method was applied in the urine sample and satisfactory results were obtained showing that this electrode is very suitable in pharmaceutical and clinical preparations. [ABSTRACT FROM AUTHOR]

For the future of fuel cells, investigations on high activity, stable, and low-cost oxygen-reduction reaction (ORR) catalysts are critical. Transition metals have attracted particular research interest in pursuit of such efficient and sustainable ORR electrocatalysts. In this work, very tiny Co nanoparticles were assembled on 3D graphene (3DG) aerogels uniformly with the help of ascorbic acid (AA) under a facile hydrothermal process. After further thermal annealing in argon, a few carbon layers are formed and wrapped on the Co nanoparticles. The synthesized materials were primarily investigated for ORR, and the experimental results indicate that the as-prepared Co/3DG shows an obviously positive onset potential (−0.01 V) and a much higher limiting current density (5.75 mA/cm) than Co/3DG prepared without using AA (−0.1 V, 4.6 mA/cm). Compared with commercial 20%Pt/C, Co/3DG prepared by using AA also displayed excellent durability and superb methanol tolerance performance, which suggests that the special structure of cobalt nanoparticles wrapped with a few carbon layers and its porous 3DG aerogel support can prevent its expansion and dissolution, improve its stability largely, and provide a new way for searching excellent ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

The present work is based on the use of a redox mediator containing an azo group for the selective determination of dopamine in the presence of uric acid and ascorbic acid by electrochemical method. A modified electrode was prepared by electrochemical polymerization of the poly 2-napthol orange film (P2NO) on the paraffin wax-impregnated graphite electrode (PIGE) by applying potential between −0.6 and 0.8 V at scan rate of 50 mV s for 30 segments. The modified P2NO film electrode was characterized by ATR-IR spectroscopy, FE-SEM, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), hydrodynamic voltammetry (HDV), and chronoamperometry (CA). The P2NO film modified electrode exhibited selective determination of dopamine in the presence of uric acid and ascorbic acid, and the electrocatalytic activity for oxidation of dopamine was excellent. The linear range for the determination of dopamine was 0.6 to 250 μM with a limit of detection of 0.13 μM. The modified P2NO electrode showed good stability and reproducibility. The modified electrode was used for real sample analysis such as human blood serum, rat blood serum, and pharmaceutical samples (dopamine hydrochloride injection). The results obtained were found to be satisfactory. [ABSTRACT FROM AUTHOR]

Rapid, reliable, reproducible, and repeatable modified sensor designs have been developed to distinguish the binary mixture of levodopa and benserazide in the presence of ascorbic acid using voltammetric techniques. Sixteen designed sensors were prepared by dropwise of different concentrations and quantities of multi-walled carbon nanotube (MWCNT) dispersions to bare glassy carbon electrode (GCE) surface and also the bottom and the top of the poly(3-methylthiophene) films. The best simultaneous determination was accomplished with the sensor dropped 20 μL of 1.0% MWCNT to GCE. Under optimum conditions, the electrocatalytic oxidation peak currents of levodopa and benserazide showed linear dynamic range, good stability, and sensitivity with detection limit of 10.3 and 32.5 μmol L, respectively. The proposed method has been successfully applied for the determination of levodopa and benserazide in urine samples and pharmaceutical preparations, demonstrating the feasibility and reliability. [ABSTRACT FROM AUTHOR]

An unconventional, flexible, disposable paper-based selective sensing platform for dopamine in the presence of ascorbic acid, suitable for wearable electronics, has been described for the first time in this work. The carbon nanotube ink-modified paper (CNIMP) in the presence of an anionic surfactant was able to discriminate effectively between dopamine and ascorbic acid thereby alleviating the difficulties associated with the sensing of dopamine in the presence of high concentration of ascorbic acid which undergoes oxidation at similar potential. The CNIMP electrode provided a large surface area in addition to its flexibility and disposability which was 25 times higher compared to a glassy carbon electrode of the same geometric area. The conductivity of the CNIMP electrodes as measured by four probe conductivity measurements was reasonably high of the order of 1.7 × 10 S cm facilitating its usefulness for the development of flexible sensors. The microscopic features of the electrodes showed the dense coverage and even distribution of carbon nanotubes on the surface with the surfactant molecules uniformly encapsulated on the surface. [ABSTRACT FROM AUTHOR]

A gold bare template modified with self-assembled layers (SAMs) composed of gold nanoparticles and organic S-containing compound: cysteamine and dihydrolipoic acid were prepared. The electrode with SAMs endowed with gold nanoparticles gave a high catalytic effect for dopamine electrooxidation alone and in the presence of biogenic interfering compounds: ascorbic acid and uric acid in solution at pH 7. For this novel sensor, a linear relationship between the current response of dopamine 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 0.85 mM with the detection limit of 0.023 μM. [ABSTRACT FROM AUTHOR]

This paper describes the development of a simple and efficient nanostructured platform based on multi-walled carbon nanotubes (MWCNT) functionalized with an in situ generated vanillic acid (VA) polymer. It was used as an analytical sensor for the simultaneous determination of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electropolymerization process of VA, performed on MWCNT-modified glassy carbon electrode, produces three redox systems based on quinone/hydroquinone functionality, as observed by cyclic voltammetry. The amperometric sensor has as figures of merit for the simultaneous determination of AA, DA, and UA the following values: for AA, a linear range of 5-120 μM and detection limit of 3.5 μM; for DA, a linear range of 5-120 μM and detection limit of 4.5 μM; and for UA, a linear range of 5-120 μM and a detection limit of 1.5 μM. From the obtained performance, the development of the platform based on MWCNT/poly-VA is justified for the simultaneous determination of AA, DA, and UA. [ABSTRACT FROM AUTHOR]

Physical and mathematical models are proposed which describe the electrochemical transformation of compounds diffusing from the solution to an ensemble of nanoparticles (i.e., nanoelectrodes), located on a solid bulk electrode surface. Electrochemical oxidation of ascorbic acid at solid electrodes (glassy carbon, Graphite Ultra Trace and gold) unmodified and modified with gold nanoparticles (Au-ensemble of nanoelectrodes) was experimentally studied. Nanoeffects and diffusion limiting current were observed in the investigation of ascorbic acid oxidation on Au electrodes. Nanoeffects manifested themselves in a shift of the oxidation potential towards negative values with decreasing size of the nanoparticles. Agreement between theoretical and experimental results was demonstrated. The shift of the peak potential or half-peak potential can be used to estimate the size of nanoparticles and Gibbs free surface energy and contribution of nanoeffects to the kinetics of the electrode process. [ABSTRACT FROM AUTHOR]

Carbon-coated LiFeSiO composite (LFS/C-AA) was synthesized via a refluxing-assisted solid-state reaction by using ascorbic acid as additive and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, galvanostatic charge/discharge measurements, and electrochemical impedance spectra (EIS) tests. The results show that ascorbic acid can to some extent prohibit the oxidation of Fe during the synthesis process, and the pyrolytic carbon from ascorbic acid shows higher electronic conductivity and improves the degree of graphitization of residual carbon in the LFS/C-AA composite. Compared with LFS/C prepared without ascorbic acid, LFS/C-AA displays better electrochemical performance. The desirable property is attributed to the reduced particle size, the enhanced electronic conductivity, and the improved diffusion coefficient of lithium ions. [ABSTRACT FROM AUTHOR]

Composites of Nafion, COOH-capped CdSe, and self-doped polyaniline (SPAN) were used to prepare novel chemical modified glassy carbon electrodes (Nafion/CdSe/SPAN/GCE). The electrocatalytic activities of the modified GCE to the redox reactions of dopamine (DA), uric acid (UA), and ascorbic acid (AA) were investigated by cyclic voltammetry (CV). CV curves revealed that the electrocatalytic activities of Nafion/CdSe/SPAN/GCE to oxidations of the analytes in solution of pH 7 were in the order of DA > UA > AA. This order was consistent with the strong-to-low extent of interactions between the modified GCE and the analytes. These interactions were consistent with the observations that the oxidation rate of DA followed a diffusion-controlled process whereas that of UA followed a surface adsorption-controlled process. The composites of casting at higher pH levels were found to exhibit better CdSe and SPAN dispersions in films and higher electrocatalytic activities. CdSe and SPAN exhibited insignificant synergistic effects on the oxidations of DA when cast from Nafion solutions of both low and high pHs whereas CdSe and SPAN exhibited much synergistic effects on the oxidations of UA when cast from the Nafion solution of high pH at 12. [ABSTRACT FROM AUTHOR]

Titanium dioxide nanoparticle/gold nanoparticle/carbon nanotube (TiO/Au/CNT) nanocomposites were synthesized, and then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). A TiO/Au/CNT nanocomposite-modified glassy carbon (GC) electrode was prepared using the drop coating method and was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric current-time response ( I- T). The modified material is redox-active. The nonenzymatically detected amount of ascorbic acid (AA) on the TiO/Au/CNT electrode showed a linear relationship with the AA concentration, for concentrations from 0.01 to 0.08 μM; the sensitivity was 117,776.36 μA · cm · (mM), and the detection limit was 0.01 μM (S/N = 3). The results indicated that the TiO/Au/CNT nanocomposite-modified GC electrode exhibited high electrocatalytic activity toward AA. This paper describes materials consisting of a network of TiO, Au, and MWCNTs, and the investigation of their synergistic effects in the detection of AA. [ABSTRACT FROM AUTHOR]

In voltammetric analysis the signal—in most cases—depends on transport processes. When getting concentration values of analytes from voltammetric calibrating curves, it is expected that the mass transport characteristics in sample solutions and in calibrating standards are identical. Standard addition methods are used in analytical practice when making calibrating standard with transport properties matching that of the samples would be difficult. Voltammetric measurements can also be carried out in soil—in sediment—or in gel samples. The mass transport conditions in these media, however, can considerably differ from those existing in aqueous solutions. The application of standard addition technique, however, is not an option there. In this work, a glassy carbon electrode was applied with a built-in diffusion layer on its measuring surface and chronoamperometric measurements were carried out. The current–time transients taken in aqueous solution and in tortuous, diffusion-hindered media were compared. Ascorbic acid and iodine as analytes as well as silica sand sediments and green pepper pulps as tortuous matrices were used. It was proved that if the modified electrode is used for analysis, then short time chronoamperometric transients taken in tortuous media can be evaluated by calibration data taken in aqueous standard solutions. [ABSTRACT FROM AUTHOR]

Cationic iron (III) tetrakis-5, 10, 15, 20-( N-methyl-4-pyridyl) porphyrin (Fe IIITMPyP) was intercalated into layered semiconductor KNb 3O 8 by ion-exchange method. The target product was characterized by XRD, Fourier transform infrared, UV–vis, and TGA. Fe IIITMPyP forms an inclined monolayer between Nb 3O 8− nanosheets and endues the nanocomposite with excellent electrochemical catalytic activities. The target nanocomposite modified glass carbon electrode shows good electrocatalytic activities for the oxidation of ascorbic acid (AA); the catalytic mechanism was proposed. Differential pulse voltammetric technique was used for detection of AA in neutral aqueous solution; a detection limit of 4.2 × 10 −5 M was obtained, and the modified electrode showed good reproducibility in electrochemical detection. [ABSTRACT FROM AUTHOR]

The silver nanoparticles doped poly-glycine composite membrane was prepared by cyclic voltammetry on the surface of the glassy carbon electrode (GCE). The morphology and electrochemical properties were characterized by scanning electron microscopy and cyclic voltammetry, respectively, and in detail, the electrochemical behaviors of the norepinephrine (NE) on this membrane were studied. The results showed that the membrane had good catalytic properties for the oxidative-reductive reaction of NE. NE had a couple of sensitive oxidative-reductive current peaks. The reductive peak currents were linearly with its concentration in the range of 1.90 × 10 to 7.00 × 10 and 7.00 × 10 to 1.00 × 10 mol l, and the linear regressive equations were i (A) = 3.73 × 10 + 0.70 C (mol l), i (A) = 9.83 × 10 + 0.12 C (mol l), respectively, with the relate coefficient ( r) of 0.9926 and 0.9944. The detection limit was 1.2 × 10 mol l (S/N = 3), which could be used to determine the content of NE and at the same time, eliminate the interference of the ascorbic acid (AA). The proposed method had high sensitivity, good selectivity and stability. [ABSTRACT FROM AUTHOR]

Triclinic LiVPOF and monoclinic LiV(PO) are synthesized through a soft chemical process with mechanical activation assist, followed by annealing. In this process, ascorbic acid is used as reducing agent as well as carbon source. The as-prepared samples are coated with amorphous carbon. XPS analysis results show the expected valency states of ions in LiVPOF and LiV(PO). The electrochemical properties of the prepared LiVPOF/C and LiV(PO)/C cathodes are evaluated. The as-prepared LiVPOF/C cathode shows an initial discharge specific capacity of 140 ± 3 mAh g at 30 mA g in the voltage range of 3.0~4.4 V, compared with that of 138 ± 3 mAh g possessed by LiV(PO)/C. Both samples exhibit good cycle performance at different current densities. The capacity delivered by LiVPOF remains 95.5 and 91.7 % of its initial discharge capacity after 50 cycles at 150 and 750 mA g, respectively, while 97.4 and 90.6 % for LiV(PO)/C. But the rate capability of LiVPOF/C is not so good compared with as-prepared LiV(PO)/C. [ABSTRACT FROM AUTHOR]

A stable and specific electrochemical biosensor based on a poly(3,4-ethylenedioxythiophene)-ethyl sulfate (PEDOT-EtSO) matrix with high conductivity and stability was easily fabricated. 1-Ethyl-3-methylimidazolium ethyl sulfate ([Emim][EtSO]), a halogen-free and relatively hydrolysis-stable hydrophilic ionic liquid, was selected as the supporting electrolyte for the one-step electrosynthesis of the PEDOT-EtSO matrix under the optimum conditions. The PEDOT-EtSO matrix electrosynthesized in the [Emim][EtSO] aqueous solution displayed high conductivity and stability. Inspired by preceding studies, the electrochemical biosensor based on the resulting PEDOT-EtSO matrix was facilely developed to determine the vitamin C (VC) level in commercial juices. Ascorbate oxidase (AO) was dip-coated on the surface of the as-prepared matrix, then Nafion was covered on the surface of AO layers for preventing the leakage of enzyme molecules. The fabricated biosensor displayed an excellent bioelectrocatalytic activity to the oxidation of VC. Under optimal conditions, the fabricated amperometric biosensor showed rapid response (less than 2 s) to VC at a low potential of 0.2 V over a wide range of concentrations from 8.0 × 10 to 1 × 10 M with a high sensitivity of 104.8 mA M cm, and the limit of detection and the limit of quantification of presented method was 0.147 μM and 0.487 μM, respectively. Moreover, the bioaffinity, specificity, stability, and reproducibility of the biosensor were also evaluated. Finally, the biosensor was employed to determine the content of VC in commercial juice samples by amperometric and voltammetric methods. The satisfactory results indicated that the as-prepared conducting PEDOT-EtSO films as immobilization matrix of biologically active species could be a promising candidate for the design and application of biosensors. [ABSTRACT FROM AUTHOR]

A simple preparation methodology able to stabilize gold nanoparticles and to obtain an electrode which detects ascorbic acid, uric acid, and dopamine by different techniques is presented. A 3-mercaptopropyl-functionalized silica network was synthesized using the sol-gel method. Gold nanoparticles (nAu) were immobilized on the material at synthesis by adding a sol of these previously prepared particles to the reaction mixture. The electrochemical behavior of the SiO/MPTS/Au carbon paste electrode was studied using cyclic voltammetry in the presence of a hexacyanoferrate probe molecule. The presence of nAu in the functionalized silica network changes the electrochemical characteristics of the material, favoring the electron transfer process of this complex ion. The SiO/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (HAA), dopamine (DA), and uric acid (UA) using square wave voltammetry techniques. With the nAu on the electrode, an increase in the peak current related to the redox process of the HAA, DA, and UA was observed. The separations of the anodic peak potentials between DA/HAA and UA/HAA were 310 and 442 mV, respectively. The results obtained show that the SiO/MPTS/Au electrode can be used in the simultaneous determination of HAA, DA, and UA. [ABSTRACT FROM AUTHOR]

A non-enzymatic amperometric sensor is developed based on the graphite electrode modified with functionalized graphene for the determination of β, d (+)-glucose. Cyclic voltammetry and electrochemical impedance spectroscopy techniques are used to study the behavior. Atomic force microscopy was used to study the surface topography of the working electrode before and after its modification. The sensor enabled the direct electrochemical oxidation of β, d (+)-glucose in alkaline medium and responded linearly to the analyte over the range from 0.5 × 10 to 7.5 × 10 M with a limit of detection of 10 μM. The sensor is found to exhibit a better sensitivity of 28.4 μA mM cm, good stability, and shelf life. The sensitivity of the sensor to β, d (+)-glucose was not affected by the commonly co-existing interfering substances such as l-ascorbic acid, dopamine, uric acid, and acetaminophen. [ABSTRACT FROM AUTHOR]

A novel and simple biosensor based on poly(indoleacetic acid) film-modified electrode (PIAA/CPE) was fabricated by electrochemical polymerization of indoleacetic acid on a carbon paste electrode (CPE) through cyclic voltammetry. The resulting electrode was characterized by scanning electron microscopy, and the electrochemical behaviors of dopamine (DA) and epinephrine (EP) at the electrode were studied. It was illustrated that PIAA/CPE had excellent electrochemical catalytic activities toward DA and EP. The anodic peak currents ( I) were dramatically enhanced by about seven-fold for DA and ten times for EP at PIAA/CPE. Thus, the determinations of DA and EP were carried out using PIAA/CPE successfully. The linear responses were obtained in the range of 3.0 × 10∼7.0 × 10 and 1.0 × 10 ∼8.0 × 10 mol L with the detection limits (3 σ) of 1 × 10 and 4 × 10 mol L corresponding with DA and EP, respectively. Moreover, the cathodic peaks of DA and EP were well-separated with a potential difference about 325 mV in pH 5.3 phosphate-buffered saline, so simultaneous determination of DA and EP was carried out in this paper. Additionally, the interference studies showed that the PIAA/CPE exhibited excellent selectivity in the presence of ascorbic acid (AA). With good selectivity and sensitivity, the present method has been successfully applied to the determination of DA and EP in pharmaceutical samples. [ABSTRACT FROM AUTHOR]

Differential pulse and cyclic voltammetry were applied for the oxidation of mixture of uric acid and ascorbic acid at the surface of carbon paste/cobalt Schiff base composite electrode. The electrooxidation of these compounds at bare electrode is sluggish, and there is no suitable peak separation between them. However, using cobalt methyl salophen as modifier, two well-defined anodic waves with a considerable enhancement in the peak current and a remarkable peak potential separation near 315 mV are obtained. It can improve the kinetics of electron transfer for both compounds remarkably. All these improvements are created because of the electrocatalytic property of cobalt Schiff base complex. The effect of some parameters such as pH and scan rates were studied. All the anodic peak currents for the oxidation of ascorbic acid and uric acid shifted toward more negative potential with an increase in pH, revealing that protons have taken part in their electrode reaction processes. The best peak separation with appropriate current was obtained for pH 4.0. A linear range of 5.0 × 10 to 1.0 × 10 and 1.0 × 10 to 1.0 × 10 M with detection limit of 8.0 × 10 and 8.0 × 10 M was obtained for ascorbic acid and uric acid using differential pulse voltammetry at the surface of modified electrode, respectively. Analytical utility of the modified electrode has been examined successfully using human urine samples and vitamin C commercial tablets. [ABSTRACT FROM AUTHOR]

We report here a green and facile one-step method to fabricate nano-network gold films of low roughness via anodization of gold electrodes in an aqueous solution of l-ascorbic acid (AA) or hydroquinone (HQ) at the oxidation peak potential. The preparation involves the formation of thin gold oxide layer by anodization of gold and its simultaneous and/or subsequent reduction by AA or HQ. The as-fabricated nano-network gold films show very strong SERS activity in comparison with the substrates prepared by some other electrochemical roughening methods. [ABSTRACT FROM AUTHOR]

Au electrode modified with the self-assembled monolayer of a heterocyclic thiol, mercaptotriazole (MTz), is used for the electroanalysis of uric acid (UA) and ascorbic acid (AA). MTz forms a less compact self-assembly on Au electrode. The self-assembly of MTz on Au electrode favors the oxidation of UA and AA at less positive potential. Significant decrease (∼400 mV) in the overpotential and enhancement in the peak current for the oxidation of interfering AA with respect to the unmodified electrode is observed. The negative shift in the oxidation peak potential of AA favors electrochemical sensing of UA without any interference. Two well-separated voltammetric peaks for AA and UA are observed in their coexistence. The large separation between the two voltammetric peaks allows the simultaneous or selective sensing of the analytes without compromising the sensitivity. Linear response is obtained for a wide concentration range. This electrode could sense as low as 1 μM of UA in the presence of 10-fold excess of interfering AA. No change in the sensitivity (0.012 μA/μM) of the electrode toward UA in the presence and absence of AA is observed. Reproducible and stable amperometric flow injection response was obtained upon repetitive injection. [ABSTRACT FROM AUTHOR]

method to fabricate poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonate)-Meldola Blue (PEDOT-PSS-MDB)-modified electrodes had been disclosed. Firstly, the PEDOT-PSS-film-modified electrode was electrochemically prepared. Then, the PEDOT-PSS was treated as a matrix to immobilize electroactive mediator, Meldola Blue (MDB), by means of an electrostatic interaction to form the proposed film, PEDOT-PSS-MDB. Electrochemical properties of the proposed film exhibited surface confinement and pH dependence. The PEDOT-PSS-MDB electrode could electrocatalytically reduce hydrogen peroxide (HO) with a low overpotential and showed a linear response to HO in the concentration range of 5 to 120 μM, detection limit of 0.1 μM, and sensitivity of 353.9 μA mM cm ( S/ N = 3). By comparison, the electrocatalytic activity of PEDOT-PSS-MDB electrode was found superior to that of PEDOT-PSS and MDB-PSS electrodes. It also has competitive potential as compared with other mediators, through the use of HRP to determine HO. Moreover, the potential interferents such as ascorbic acid, dopamine, uric acid, and glucose were also studied for HO determination by the proposed film. [ABSTRACT FROM AUTHOR]

Preanodized screen printed carbon electrode (SPCE) has been utilized for the detection of propofol. Here the preanodized SPCE possess the specific functional groups which help the detection and determination of propofol. The proposed SPCE shows a clear oxidation peak for the detection of propofol in pH 7.0 phosphate buffer solutions. Interestingly, it shows a well-defined individual oxidation peak for the detection of propofol in the presence interferences (mixture of ascorbic acid, dopamine, and uric acid). This type of pretreated SPCE successfully enhances the electrooxidation current and overcomes the interference effects and clearly exhibits the signals for the propofol detection using cyclic voltammetry and flow injection analysis techniques. The preanodized SPCE shows the electrooxidation signals for the propofol detection in the linear range of 0.09 to 0.90 μM, respectively. Further, the sensitivity of the proposed electrode for the propofol detection is found to be 3.6 μA μM. [ABSTRACT FROM AUTHOR]

multiwalled carbon nanotubes (MWNT) modified glassy carbon electrode (GCE) coated with poly(orthanilic acid) (PABS) film (PABS-MWNT/GCE) has been fabricated and used for simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA) by differential pulse voltammetry (DPV). Scanning electron microscopy, Fourier transform infrared spectra, and electrochemical techniques have been used to characterize the surface morphology of the PABS-MWNT composite film and the polymerization of ABS on electrode surface. In comparison with the bare GCE and the MWNT-modified GCE, the PABS-MWNT composite film-modified GCE, which combines the advantages of MWNT and the self-doped PABS, exhibits good selectivity and sensitivity for the simultaneous and selective determination of UA and DA in the presence of AA. Due to the different electrochemical responses of AA, DA, and UA, PABS-MWNT/GCE can resolve the overlapped oxidation peak of DA and UA into two well-defined voltammetric peaks with enhanced current responses using both cyclic voltammetry (CV) and DPV. The peak potential separations between DA and UA are 170 mV using CV and 160 mV using DPV, respectively, which are large enough for the selective and simultaneous determination of these species. In the presence of 0.5 mM AA, the DPV peak currents are linearly dependent on the concentration of UA and DA in the range of 6-55 and 9-48 μM with correlation coefficients of 0.997 and 0.993, respectively. The detection limits ( S/ N = 3) for detecting UA and DA are 0.44 and 0.21 μM, respectively. The PABS-MWNT/GCE shows good reproducibility and stability and has been used for the simultaneous determination of DA and UA in the presence of AA in samples with satisfactory results. [ABSTRACT FROM AUTHOR]

The present study focuses on the specific role of the number, size, and shape of copper crystals electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) layers for the electroanalytic determination of dopamine (DA). It is shown that the type of the metal deposit is significantly influenced by the thickness of the polymer layer and the type of copper ions plating solutions, e.g., copper sulfate or copper oxalate. By combining electrochemical measurements and scanning electron microscopic investigations, it is found that the loss of electroactivity for DA oxidation, established for Cu deposited on thick PEDOT layers (from copper sulfate solution), relates to the instability of small needle-like Cu crystals decorating the PEDOT surface in this case. Large (several micrometer-sized) copper crystals (as deposited on thin PEDOT layers from copper sulfate solution) are found to suffer surface destruction along the crystalline edges when exposed to electrochemical treatment in the presence of DA. Finally, smaller (∼0.5 µm) bulky crystals with a large surface coverage (up to 30%), as deposited from copper oxalate solution, are found to provide a stable and highly sensitive Cu–PEDOT composite material operating in the nanomolar DA concentration range. Differential pulse voltammetry measurements carried out in the 6 nM to 2 µM DA concentration range, in the presence of large excess (1 to 5 mM) of ascorbic acid, show two regions of linear response with different sensitivities, 9 nA nM and 0.313 µA µM, respectively. [ABSTRACT FROM AUTHOR]

The oxidation of ascorbic acid (AA) and dopamine (DA) is studied on non-modified and copper crystal-modified poly(3,4-ethylenedioxythiophene) (PEDOT)-coated electrodes. Both oxidation reactions are studied for different thickness of the polymer layers. For several microns thick PEDOT layers both PEDOT and Cu-modified PEDOT show the largest currents. A stable voltammetric response for AA oxidation is observed together with a linear dependence of the peak currents on concentration in the 0.3 to 6.0 mM range. For DA oxidation, however, a gradual loss of electroactivity is found with increasing number of voltammetric scans and concentration. This problem is overcome by using thinner (<1 µm) polymer layers. In the presence of both AA and DA, the Cu-modified PEDOT-coated electrodes provide better selectivity with respect to DA in comparison to non-modified PEDOT due to partial suppression of the AA oxidation currents. Thin PEDOT layers modified with electrodeposited Cu crystals show a stable and sensitive response for DA oxidation in the micromolar concentration range. A linear dependence of the voltammetric peak currents is found in a wide concentration range (from 6 to about 200 µM) of DA in the presence of a large excess (1 mM concentration) of AA. The sensitivity is 0.013 µA µM. [ABSTRACT FROM AUTHOR]

In the present work, the aluminum electrode surface was modified with a thin layer of palladium by dipping its polished surface in a 25% ammonia solution of PdCl2. The electrocatalytic ability of the modified electrode towards the paracetamol (PCT), ascorbic acid (AA), and codeine (CO) oxidation was investigated using cyclic voltammetry, chronoamperometry. The number of electrons for rate-determining step and diffusion coefficient of PCT, AA, and CO were determined. The electro-oxidation pathway and kinetics, including transfer coefficient α and diffusion coefficient D, are estimated. The results indicated that the simultaneous voltammetry of the three compounds was possible in a mixture solution. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode (GCE) modified with docosyltrimethylammonium chloride (DCTMACl) is used for simultaneous determination of dopamine (DA) and ascorbic acid (AA) using differential pulse voltammetry (DPV) technique in 0.10 mol·L−1 phosphate buffer solution of pH 5.0. The cationic surfactant DCTMACl modified film has a positive charge. DA exists as the positively charged species, whereas AA is the negatively charged one in the solution. Thus, at DCTMACl film-modified GCE, the oxidation peak potential of AA shifts toward less negative potential and the peak current of AA increases a little, while the oxidation peak potential of DA shifts toward more positive potential and peak current decreases greatly in comparison with that on bare electrode. The two anodic peaks are separated around 200 mV. Under optimal conditions, the catalytic peak currents obtained from DPV increase linearly with concentrations of DA and AA in the ranges of 1.0 × 10−5 to 1.0 × 10−3 mol·L−1. This electrode has good reproducibility, high stability in its voltammetric response, and low detection limit (micromolar) for both AA and DA. The modified electrode has been applied to the determination of DA and AA in injection. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (GNs) could be efficiently immobilized on binary mixed self-assembled monolayers (SAMs) on a gold surface composed of 1,6-hexanedithiol and 1-octanethiol (nano-Au/SAMs gold electrode). This GN chemically modified electrode was used for electrochemical determination of ascorbic acid (AA) and dopamine (DA) in aqueous media. The result showed that the GN-modified electrode could clearly resolve the oxidation peaks of AA and DA, with a peak-to-peak separation (∆ Ep) of 110 mV enabling determination of AA and DA in the presence of each other. The linear analytical curves were obtained in the ranges of 0.3–1.4 mM for AA and 0.2–1.2 mM for DA concentrations using differential pulse voltammetry. The detection limits (3 σ) were 9.0 × 10−5 M for AA and 9.0 × 10−5 M for DA. [ABSTRACT FROM AUTHOR]

A glassy carbon electrode (GCE) modified with the film composed of chitosan incorporating cetylpyridine bromide is constructed and used to determine uric acid (UA) and ascorbic acid (AA) by differential pulse voltammetry (DPV). This modified electrode shows efficient electrocatalytic activity and fairly selective separation for oxidation of AA and UA in mixture solution. UA is catalyzed by this modified electrode in phosphate buffer solution (pH 4.0) with a decrease of 80 mV, while AA is catalyzed with a decrease of 200 mV in overpotential compared to GCE, and the peak separation of oxidation between AA and UA is 260 mV, which is large enough to allow the determination of one in presence of the other. Under the optimum conditions, the anodic peak currents (Ipa) of DPV are proportional to the concentration of UA in the range of 2.0x10-6 to 6.0x10-4 M, with the detection limit of 5.0x10-7 M at a signal-to-noise ratio of 3 (S/N=3) and to that of AA in the range of 4.0x10-6 to 1.0x10-3 M, with the detection limit of 8.0x10-7 M (S/N=3). [ABSTRACT FROM AUTHOR]

Abstract  A chemically modified carbon-paste electrode (CPE) is prepared by incorporating congo red (CR) immobilized on multi-walled carbon nanotube (MWCNT). The results show that CR is effectively immobilized on the surface of MWCNT under the ultrasonic agitation in aqueous solution and further incorporating the nafion. The prepared electrode, due to the electrostatic repulsions between the CR and ascorbate anion, is capable to mask the response of the ascorbic acid (AA) completely and provide an effective method for the detection of minor amounts of uric acid (UA) in the presence of high concentrations of AA. On the other hand, an increase in the microscopic area of the electrode by addition of MWCNT together with the electrocatalytic activity caused to a significant enhancement in the voltammetric response to UA. Optimization of the amounts of composite modifier in the matrix of CPE is performed by cyclic and differential pulse voltammetric measurements. The modified electrode shows a linear response to UA in the range of 1.0 × 10−7–1.0 × 10−4 M with a detection limit of 1.0 × 10−8 M. The electrode exhibits excellent accuracies for the determination of UA in the presence of high concentrations of AA (a recovery of 97.6%). The response of the electrode toward sulfhydryl compounds such as cysteine, penicillamine, and glutathione is not considerable. This reveals a good selectivity for the voltammetric response toward UA. The effective electrocatalytic property, ability for masking the voltammetric responses of the other biologically reducing agents, ease of preparation, and surface regeneration by simple polishing together with high reproducibility and stability of the responses make the modified electrode suitable for the selective and sensitive voltammetric detection of sub-micromolar amounts of UA in clinical and pharmaceutical preparations. [ABSTRACT FROM AUTHOR]

Abstract  A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s−1 with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10−5−1.2 × 10−3 and 1.0 × 10−6−4.0 × 10−5 mol L−1 in 0.15 mol L−1 phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination of DA and AA in real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract  Multilayered nanostructured films have been widely investigated for electrochemical applications as modified electrodes, including the layer-by-layer (LbL) films where properties such as thickness and film architecture can be controlled at the molecular level. In this study, we investigate the electrochemical features of LbL films of poly(o-methoxyaniline; POMA) and tetrasulfonated phthalocyanines containing nickel (NiTsPc) or copper (CuTsPc). The films displayed well-defined electroactivity, with redox pairs at 156 and 347 mV vs SCE, characteristic of POMA, which allowed their use as modified electrodes for detecting dopamine and ascorbic acid at concentrations as low as 10-5 M. [ABSTRACT FROM AUTHOR]