Pretreated Glassy Carbon Electrode Research Articles

Signal Generation at an Electrochemical Immunosensor via the Direct Oxidation of an Electroactive Label

AbstractIn this paper, we report the development of an electrochemical immunosensor with a direct signal generation scheme. To achieve this, ferrocenecarboxylic acid was conjugated as an electroactive label to an immunocomplex immobilized on an electrochemically pretreated glassy carbon electrode. The pregnancy hormone and tumor marker, human chorionic gonadotrophin (hCG), was employed as a model analyte. Direct oxidation of ferrocenecarboxylic acid facilitated a signal generation scheme for the quantification of hCG at the immunosensor. Evaluation of the immunosensor performance has yielded statistically acceptable agreement in hCG levels present in several human serum samples compared to those reported by a Sydney hospital.

Development of a Biosensor for the Detection of Carcinoembryonic Antigen Using Faradic Impedance Spectroscopy

Abstract A direct and simple method has been proposed to immobilize carcinoembryonic antibody (anti-CEA) on the surface of nanogold-modified glassy carbon electrode. Colloidal Au was electrodeposited onto the surface of pretreated glassy carbon electrode (GCE) as immobilization matrix to amplify response signal, then anti-CEA was absorbed on nanogold by amino group and physical absorption. The impedance change occurred on the sensor surface due to the specific immuno-interaction was utilized to determine carcinoembryonic antigen (CEA). Tests revealed significant change in the electron-transfer resistance (Ret) to various concentration of CEA in Fe(CN)63−/4− probe solution. The assay also demonstrates that the immunoelectrode exhibits a high level of sensitivity and satisfied response range.

Phenylboronic acid self-assembled layer on glassy carbon electrode for recognition of glycoprotein peroxidase

We have successfully fabricated a phenylboronic acid self-assembled layer on glassy carbon electrodes (GCE), where 3-aminophenylboronic acid (APBA) is covalently bound to the electrochemical pretreated GCE surface with glutaraldehyde linkage. The specific binding of glycoprotein peroxidase with the self-assembled layer has been studied using horseradish peroxidase (HRP) as a model glycoprotein. Cyclic voltammetric, electrochemical impedance studies and photometric activity assays show that the affinity interaction of HRP with the APBA modified GCE surface includes specific and nonspecific bonding. The specific binding is attributed to the boronic acid–diols interaction where the boronic acid specifically binds the glycosylation sites of the HRP. This specific binding is reversible and can be split by sorbitol and glucose or released in an acidic buffer. The catalytic current of the HRP-loaded electrode, due to the catalytic oxidation of thionine in the presence of hydrogen peroxide, is proportional to HRP concentrations of the incubation solution. This work offers a new way to build novel sensors by specific binding of glycoproteins to a boronic acid self-assembled layer for determination of glycated proteins.

Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode

The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l(-1) NH(3)-NH(4)Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH(3)-NH(4)Cl buffer (pH 9.0) at a potential of -0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 microg ml(-1) to 50.0 microg ml(-1). The detection limit (three times the signal-to-noise) was 1.0 microg ml(-1) and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 microg ml(-1) medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.

Voltammetric determination of aluminum(III) using a reagentless sensor fabricated by sol–gel process

The electrochemical behavior of alizarin red S (1,2-dihydroxyanthraquinone sulfonate, ARS) immobilized on electrochemically pretreated glassy carbon (GC) electrode by silica sol–gel process was investigated. The central quinone functionalities of the ARS molecule underwent quasi-reversible redox reaction. Oxidation of the dihydroxyl functionalities gave unstable products which underwent further follow-up chemical transformation to give new electroactive species. The results were applied to develop a reagentless sensor for the indirect determination of aluminum (Al) ions. Various experimental parameters, which influenced the properties of the modified electrode, were optimized. Under the optimum experimental conditions, the linear response range for Al 3+ ions employing differential pulse voltammetry was 1.4×10 −7 to 1.4×10 −6 mol l −1 and the relative standard deviation for 1×10 −6 mol l −1 Al 3+ was 2.7% ( n=7). The detection limit was 8×10 −8 mol l −1 . The modified electrode, as a reagentless sensor, is stable and portable. This method has been applied to determine Al in water samples.

A Novel Method for Separating the Anodic Voltammetric Peaks of Dopamine and Ascorbic Acid

This paper presents a simple and reliable method for separating the anodic peaks of dopamine (DA) and ascorbic acid (AA). Good electrochemical responses of DA and AA can be obtained at an electrochemically pretreated glassy carbon electrode (PGCE). The electrode reaction of DA is a quasi-reversible process, but the oxidation of AA is entirely irreversible. Consequently, the PGCE can be used to separate the anodic peaks of DA and AA. The separation can be higher than 290 mV, and the detection limit (S/N=3) of DA is 6.0×10−8 M. This PGCE is very stable and can be used for as long as four weeks.

Electrooxidation and Amperometric Detection of Ascorbic Acid at GC Electrode Modified by Electropolymerization of N,N‐Dimethylaniline

AbstractThe polymer film of N,N‐dimethylaniline (DMA) is deposited on the electrochemically pretreated glassy carbon (GC) electrode by continuous electrooxidation of the monomer. This poly N,N‐dimethylaniline (PDMA) film‐coated electrode can be used as an amperometric sensor of ascorbic acid (AA). The polymer film (thickness (ϕ): 0.3±0.02 μm) having positive charge in its backbone attracts the anionic species AA. Thus, the anodic peak potential (350 mV vs. Ag|AgCl|NaCl(sat)) for the oxidation of AA at the bare electrode is largely shifted to the negative value (150 mV) at this electrode. The PDMA film‐coated electrode is stable in acidic, alkaline and neutral media and can sense AA at different pH's. The diffusion coefficients of AA in solution (D) and in film (Ds) were estimated by rotating disk electrode voltammetry: D=(5.5±0.1)×10−6 cm2 s−1 and Ds=(6.3±0.2)×10−8, (6.0±0.2)×10−8 and (4.7±0.2)×10−8 cm2 s−1 for 0.5, 1.5 and 3.0 mM AA, respectively. A permeability of AA through the PDMA film was found to decrease with increasing the concentration of AA in the solution. In the chronoamperometry, the current response for the oxidation of AA at different times elapsed after potential‐step application is linearly increased with the increase in AA concentration in a wide range of its concentration from 25 μM to 1.65 mM. In the hydrodynamic amperometry, a successive addition of 10 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.178 μA cm−2 μM−1. So, the fouling of the electrode surface caused by the oxidized product of AA is markedly eliminated at this PDMA film‐coated electrode. A flow injection analysis based on the present electrode was performed to estimate the concentration of vitamin C in fruit juice.

Adhesion of gold nanoparticles on an electrochemically pretreated glassy carbon electrode.

This study describes a simple new method for the adsorption of gold nanoparticles on a glassy carbon (GC) electrode. By electrochemically oxidizing the GC electrode and immersing it into a gold colloidal solution, one could induce the adhesion of the gold nanoparticles. The image of the field emission scanning electron microscopy confirmed that the nanoparticles were evenly distributed over the surface. A 2-aminoethanethiol self-assembled monolayer was formed on the surfaces of the adsorbed gold nanoparticles and a reductive desorption wave was observed during the reduction of the adsorbed 2-aminoethanethiol.

Simultaneous Electroanalysis of Nitric Oxide and Nitrite

The simultaneous sensing of nitric oxide (NO) and its metabolite, nitrite <TEX>$(NO_2^-)$</TEX> has been studied by Osteryoung square-wave voltarnmetery (OSWV) in physiological pH solution (0.1 M phosphate buffer solution, pH 7.2). Using an electrochemically pretreated glassy carbon (GC) electrode, OSWV was successfully applied to observe the well-separated oxidation peaks at ca. 0.58 and 0.80V vs. Ag/AgCI for NO and <TEX>$(NO_2^-)$</TEX>, respectively. This clear separation between the NO and <TEX>$(NO_2^-)$</TEX> oxidation peaks may be due to the formation of surface oxides (e.g., quinone (C=O) or carboxylic <TEX>$(COO^-)$</TEX> group) and surface defects introduced by the electrochemical pretreatment of GC electrodes.

Use of electrochemically pretreated glassy carbon electrodes as pH sensors in potentiometric titrations

The potentiometric response of glassy carbon (GC) electrodes pretreated by cycling consecutively the potential in the range 0.2 to −0.8 V was examined. The electrochemical treatment creates microchannels at the electrode surface through which cations may intercalate. A linear response to H + ions concentrations in the range 10 −2 to 10 −5 M was observed, with a slope of 60 mV per pH and a response time of 40 s for 80% response. The electrode showed an excellent performance in pH potentiometric titrations, results for synthetic and real acid samples being in agreement with those obtained by using a glass electrode. Cross-sensitivity tests for other cations (Na +, K + and Ba 2+) were also performed and the results indicated a correlation between the solvated ionic radius and the intercalation effect responsible for the sensor’s response.

Simultaneous determination of guanine and adenine in DNA using an electrochemically pretreated glassy carbon electrode

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml −1 (3×10 −8 mol l −1) and 4 ng ml −1 (3×10 −8 mol l −1), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25–5 μg ml −1.

ADSORPTIVE VOLTAMMETRIC DETERMINATION OF ORTHOPHOSPHATE AT A GLASSY CARBON ELECTRODE

A simple, rapid and sensitive method for the adsorptive voltammetric determination of trace amounts of orthophosphate is described. In order to obtain a flat background current curve, the conditions for the preparation of a glassy carbon electrode and the voltammetric measurements are optimized. Orthophosphate is accumulated as heteropoly blue on the pretreated glassy carbon electrode in an aqueous acidic molybdate solution containing vanadate and acetone at −0.2 V vs. the saturated calomel electrode (SCE) for 150 s with stirring, and then the reduced complex is reoxidized during a positive-going scan at a rate of 50 mV s−1 to 0.2 V vs. SCE. Only one distinct peak is found at around 0.01 V vs. SCE. The calibration graph is linear over the 1 × 10−7to 1 × 10−6mol dm−3 concentration range of orthophosphate and passed through the origin, with a relative standard deviation (n = 6) of 4.3% for 5 × 10−7mol dm−3. The detection limit (3σ) was 1 × 10−8mol dm−3 (1.0 ng cm−3). Arsenate, which forms heteropoly acid wi...

ELECTROCHEMICAL BEHAVIOR AND SIMULTANEOUS DETERMINATION OF VITAMIN B2, B6, AND C AT ELECTROCHEMICALLY PRETREATED GLASSY CARBON ELECTRODE

An electrochemically pretreated glassy carbon electrode (PGCE) was achieved by anodic oxidation at 1.8V and following potential cycling in the potential range from −0.8 to +1.0 V. The resulting PGCE gave well-defined redox peaks with E pa= −0.073 V, E pc = 0.044 V. The PGCE showed good activity in improving the electrochemical responses of some water-soluble Vitamins, such as Vitamin (VB2), Vitamin (VB6) and Vitamin (VC). VB2, VB6 could be adsorbed at PGCE and VC proceeded with an electrocatalytic process. The electrochemical behavior of VB6 at PGCE depended on the potential scanning method and the pretreatment process of the electrode. The PGCE was rather stable and can be used to simultaneously determine these vitamins in multivitamin tablets.

Voltammetric Behavior and Detection of DNA at Electrochemically Pretreated Glassy Carbon Electrode

Electrochemical oxidation of thermally denatured DNA at an electrochemically pretreated glassy carbon electrode was studied by means of adsorptive stripping voltammetry. The sensitivity for thermally denatured DNA detection at GCE was improved greatly by modifying the electrode with a simple and effective electrochemical oxidation at +1.75 V (vs. SCE) for 300 s in pH 5.0 phosphate buffer. Thermally denatured DNA was preconcentrated at pretreated GCE by its adsorption in open circuit for 5 min or at the potential of +0.3 V for 90 s, and produced two well-defined oxidation peaks of guanine and adenine residues at +0.80 V and +1.11 V in pH 5.0 phosphate buffer, respectively, while the native DNA almost did not appear at the same condition. This adsorptive stripping method can be used to study the properties of DNA using simple CV technique. A convenient quantitation of the low level of thermally denatured DNA was proposed. The detection limit of thermally denatured DNA was ca. 2.0 μg mL−1 when the accumulation time is 150 s at the potential of +0.3 V. As comparison, the acid-denatured DNA (treated in HClO4 solution) was tested at the same condition and a detection limit of 0.10 μg mL−1 was obtained.

Preconcentration and Electrochemical Determination of Nitropyrene at Electrochemically Activated Glassy Carbon Electrodes

Polycyclic aromatic hydrocarbons substituted with one or more nitro-groups (nitro-PAHs) have been proven to be carcinogenic. This work provides the first report on the electroanalysis of nitro-PAHs using chemically modified electrodes. A representative nitro-PAH species, namely nitropyrene was readily extracted onto electrochemically pretreated glassy carbon electrodes (pGCE) from methanol solution. The nitropyrene species adsorbed on pGCE were reduced electrochemically to aminopyrene in a 6-electron process in 0.5 M H2SO4. Both nitropyrene and aminopyrene were found to adsorb strongly on pGCE. Experimental results showed that the peak current resulting from nitropyrene reduction was proportional to the concentration in their methanol solution for a wide dynamic range from 5 to 1500 ng/mL with a large slope of 0.0864 A L g–1 and a correlation coefficient of 0.999. The preconcentration and determination conditions, as well as possible interference from other PAH species, were investigated. Possible application in the determination of nitropyrene in air particulate was evaluated.

Adsorptive stripping voltammetric determination of erythromycin at a pretreated glassy carbon electrode

The voltammetric behavior of the antibiotic erythromycin and its determination was described. Erythromycin was found to give one oxidative peak by cyclic voltammetry at a glassy carbon electrode which was electrochemically treated in 0.025 mol l −1 NH 3–NH 4Cl (pH 9.0) solution for 6 min. The reverse cyclic voltammograms did not show any reductive peaks. An adsorptive stripping voltammetric method for the determination of the antibiotic erythromycin at an electrochemically pretreated glassy carbon electrode has been developed. Erythromycin was accumulated in NH 3–NH 4Cl (pH 9.0) medium at the potential of +0.2 V (vs. Ag/AgCl electrode) for a certain time and then determined by second differential anodic stripping voltammetry. The second-order differential peak current ( e″) at +0.86 V, at a scan rate of 445 mV s −1, was a linear function of concentration of erythromycin in the range 2.5×10 −8∼3.5×10 −7 mol l −1 (90 s preconcentration) and 1.2×10 −8∼2.5×10 −7 mol l −1 (120 s preconcentration), and the detection limit was 5.0×10 −9 mol l −1 (4 min preconcentration). The method has been applied to the determination of erythromycin in commercial tablets and spiked urine samples with satisfactory results. The relative standard deviation ( n=5) was less than 4.5%.

Mechanism of activation of glassy carbon electrodes by cathodic pretreatment

The performance of carbon electrodes depends on the surface pretreatment methods. An exclusively cathodically pretreated glassy carbon electrode (GCE) shows very good activity towards monomeric molybdate(VI) ion adsorption and its reduction. X-ray photoelectron spectroscopy studies reveal the creation of >C–O– surface groups on cathodisation. A strong interaction between the Mo(VI) ion and these >C–O– surface groups with the formation of Mo(V) is responsible for the activation of the cathodically pretreated GCE surface.

Voltammetric behavior of alizarin red S adsorbed on electrochemically pretreated glassy carbon electrodes

The electrochemical behavior of alizarin red S (dihydroxyanthraquinonesulfonate, ARS) adsorbed on electrochemically preanodized glassy carbon electrodes was studied by cyclic voltammetry. The adsorption of ARS was greatly enhanced by the electrochemical pretreatment of the electrodes. The central quinone functionalities of the adsorbed ARS underwent quasi-reversible reduction to give stable products. Oxidation of the dihydroxyl functionalities gave unstable products which underwent further follow-up chemical transformation to give new electroactive species. The products of the chemical transformation of the oxidized species could be further oxidized at a more positive potential, resulting in two pairs of quasi-reversible, quinone-like redox waves.

Electroactivity of Redox Probes Encapsulated within Sol-Gel-Derived Silicate Films

The electroactivity of redox probes encapsulated within a silicate film prepared by the sol-gel process has been investigated to provide specific information about dopant stability, entrapment, and activity. Redox probes of different charges and sizes were physically doped into a sol prepared by the acid-catalyzed hydrolysis and condensation of tetramethoxysilane. The doped sols were then spin cast on pretreated glassy carbon electrodes, dried, and placed in a 0.1 M KNO 3 electrolyte solution. The voltammetry of the gel-doped anionic probes (i.e., potassium ferricyanide (Fe(CN) 6 3-/4- ), iridium(IV) chloride (IrCl 6 2-/3- ) , potassium octacyanomolybdate(IV) (Mo(CN) 8 4-/3- )) was stable as the film remained in solution and/or the electrode potential continuously cycled. For the gel-doped cationic or neutral probes (i.e., ruthenium(III) hexaammine (Ru(NH 3 ) 6 3+/2+ ), ruthenium(II) tris(bipyridine) (Ru(bpy) 3 2+/3+ ), ferrocenemethanol (FcCH 2 OH 0/+ )), a significant reduction in the Faradaic current was observed. UV-vis spectroscopy of the electrolyte solution after electrochemical cycling of gel-encapsulated Ru(bpy) 3 2+/3+ confirmed that the dopant leached out of the film. The percentage ofelectroactive reagent was determined for Fe(CN) 6 3-/4- and Ru(bpy) 3 2+ and found to be 3-9% and 5-10%, respectively, consistent with entrapment in a compact, dense matrix. With the exception of the much larger Ru(bpy) 3 2+/3+ , which exhibited peak-shaped voltammetry, the electrochemical behavior of the electroactive fraction of the entrapped redox probes corresponded to a surface-confined process.

Unusual activation of glassy carbon electrodes for enhanced adsorption of monomeric molybdate(VI)

Abstract We have found that an exclusively cathodically pretreated glassy carbon electrode, which has been hitherto considered ineffective in many redox systems, is highly activated towards monomeric Mo(VI) adsorption and its reduction. The most commonly used anodic pretreatment produces an inactive GCE surface with poor response. X-ray photoelectron spectroscopy has been used to probe the surface concentration change of O- and C-containing species with the pretreatment, and identify the nature of the molybdate species adsorbed on the pretreated GCE surfaces. The results obtained clearly show that the precathodisation produces > CO-surface groups, and that there is a correlation between the saturation surface coverage of Mo(VI) determined by cyclic voltammetry experiments and the alcohol O/total O ratio of the pretreated electrodes calculated from XPS measurements. The unusual activation by precathodisation is explained by a mixed potential mechanism .