Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.     

Determination of Uric Acid in the Presence of Ascorbic Acid Using Poly(3,4‐ethylenedioxythiophene)‐Modified Electrodes

A poly(3,4‐ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode (GCE) was used to determine uric acid in the presence of ascorbic acid at physiological pH facilitating a peak potential separation of ascorbic acid and uric acid oxidation (ca. 365 mV), which is the largest value reported so far in the literature. Also, an analytical protocol involving differential pulse voltammetry has been developed using a microchip electrode for the determination of uric acid in the concentration range of 1 to 20 μM in presence of excess of ascorbic acid.     

Electrochemical Oxidation and Sensitive Determination of Pyrogallol at Preanodized Screen‐Printed Carbon Electrodes

In this study, we report a simple, low‐cost and rapid electrochemical sensor based on the anodically pretreated screen‐printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow‐injection amperometric methods. A linear calibration plot was obtained for 10‐1000 μM pyrogallol with a slope of 0.0562 μA/μM. The detection limit (S/N = 3) was 0.33 μM. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.     

Microliter Volume Determination of Cosmetic Mercury with a Partially Crosslinked Poly(4‐vinylpyridine) Modified Screen‐Printed Three‐Electrode Portable Assembly

We successfully demonstrated microliter (μL) volume determination of Mercury (Hg) using an in‐built screen‐printed three electrodes containing partially crosslinked poly(4‐vinlylpyridine) (designated as pcPVP) modified carbon‐working, carbon‐counter, and Ag⁺‐quasireference electrodes (SPE/pcPVP) in a pH 4 acetate buffer solution with 2 M KCl by using the square wave anodic stripping voltammetric (SWASV) technique. Instrumental and solution phase conditions were systematically optimized. Experiments were carried out by simply placing a 500 μL‐droplet of Hg containing real sample mixed with the base electrolyte on the SPE/pcPVP surface. The SPE/Ag⁺ quasi‐reference system shifted the Hg‐SWASV detection potential ca. 250 mV positive, but the quantitative current values were appreciably similar to that of a standard Ag/AgCl reference electrode. Under optimal condition, the calibration graph is linear in the window of 100–1000 ppb of the Hg droplet system with a detection limit of 69.5 ppb (S/N=3). Finally real sample assays were demonstrated for prohibited cosmetic Hg containing skin‐lightening agents in parallel with ICP‐OES measurements.     

Sensitive Stripping Determination of Cadmium(II) and Lead(II) on Disposable Graphene Modified Screen‐Printed Electrode

In the present work, a sensitive, facile and disposable sensing platform for trace analysis of heavy metal ions was developed at the Bi modified graphene‐poly(sodium 4‐styrenesulfonate) composite film screen printed electrode (GR/PSS/Bi/SPE). The GR/PSS/Bi/SPE improved sensitivity and linearity due to the functionalization of graphene with negatively charged PSS providing more absorbing sites. The detection limit of the GR/PSS/Bi/SPE is found to be 0.042 µg L^?1 for Cd²⁺ and 0.089 µg L^?1 for Pb²⁺ with linear responses of Cd²⁺ and Pb²⁺ in the range of 0.5–120 µg L^?1. Finally, the practical application was confirmed in real water with satisfactory results.     

Screen Printed Carbon Electrode Modified with Poly(L‐Lactide) Stabilized Gold Nanoparticles for Sensitive As(III) Detection

Poly(L ‐lactide) stabilized gold nanoparticles (designated as PLA–Au^NP) with an average particle size of ca. 10 nm were used to modify a disposable screen‐printed carbon electrode (SPE) for the detection of As(III) by differential pulse anodic stripping voltammetry. Gold modification was evaluated by cyclic voltammetry, whereas scanning electron microscopy and transmission electron microscopy revealed the size and distribution of gold nanoparticles. The PLA–Au^NP/SPE was applied effectively to detect toxic As(III) in HCl medium. Under the optimal experimental conditions, a linear calibration curve up to 4 ppm with a detection limit (S/N=3) of 0.09 ppb was obtained. The sensitivity was good enough to detect As(III) at levels lower than the current EPA standard (10 ppb). Most importantly, the PLA–Au^NP/SPE can be tolerable from the interference of Cu, Cd, Fe, Zn, Mn, and Ni and hence provides a direct and selective detection method for As(III) in natural waters. Practical utility of the PLA–Au^NP/SPE was demonstrated to detect As(III) in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei‐Men).     

Facile Fabrication of Zirconia Modified Screen‐Printed Carbon Electrodes for Electrochemical Sensing of Phosphate

We report here a facile method to immobilize zirconia nanoparticles on a disposable screen‐printed carbon electrode (designated as ZrO₂‐SPCE) for phosphate sensor application. Simply by ultrasonicating a bare SPCE in a ZrO₂ slurry, ZrO₂ nanoparticles can be immobilized effectively on the electrode surface as verified by surface characterization evidences. Using ferricyanide as a redox probe, an increase in the charge transfer resistance (R_ct) of ferricyanide upon adsorption of phosphate on ZrO₂ is used for the determination of phosphate. This ZrO₂‐SPCE phosphate sensor shows a wide linear range up to 1 mM and a detection limit of 1.69 µM (S/N=3). Practical applicability of the ZrO₂‐SPCE is demonstrated by detecting phosphate content in human blood samples.     

Fast Electrochemical Characterization of Historical Glasses Using Carbon Screen‐Printed Electrodes and Ultrasonic Assisted Sampling

A new method for lead oxide (PbO) analysis in glasses, using a carbon screen printed electrode (SPE) is proposed. A suspension of the powdered glass sample in nitric acid is prepared using an ultrasonic probe, 100 µL of slurry are deposited on the SPE and the voltammetric measurement is carried out. Structural information of PbO in the glass matrix is obtained by CV. Lead quantification is performed by DPV. In the best conditions a LOD of 2.30 wt% of PbO was obtained. The method has been applied with good results in the analysis of historical glasses samples.     

Sensitive Electrochemical Detection of Horseradish Peroxidase at Disposable Screen‐Printed Carbon Electrode

A rapid, simple and sensitive electrochemical assay of horseradish peroxidase (HRP) performed on disposable screen‐printed carbon electrode was developed. HRP activities were monitored by square‐wave voltammetric (SWV) measuring the electroactive enzymatic product in the presence of o‐aminophenol and hydrogen peroxide substrate solution. SWV analysis demonstrated a greater sensitivity and shorter analysis time than the widely used amperometric and differential‐pulsed voltammetric methods. The voltammetric characteristics of substrate and enzymatic product as well as the parameters of SWV analysis were optimized. Under optimized conditions, a linear response for HRP from 0.003 to 0.1 U/mL and a detection limit of 0.002 U/mL (1.25×10^?15 mol in 25 μL) were obtained with a good precision (RSD=8%; n=6). This rapid and sensitive HRP assay with microliter‐assay volume could be readily integrated to portable devices and point‐of‐care (POC) diagnosis applications.     

Screen‐Printed Electrodes for Amperometric Determination of Iodide

An amperometric method for the determination of iodide ions has been developed using disposable, screen‐printed electrodes. The used sensors have a gold, graphite and platinum working electrodes with an area of about 7 mm². Calibration curves exhibit a linear relationship between the electrode response and the iodide concentration up to 3.00 mM. The correlation coefficients for all calibration curves varied from 0.988 to 0.998. The relative standard deviations were equal to or less than 5.26 % (n=5). The lowest iodide concentration measured was 100 µM.     

Preparation of Poly(3,4‐ethylenedioxythiophene) in a Chiral Nematic Liquid‐Crystal Field

Summary: The 3,4‐ethylenedioxythiophene (EDOT) monomer in a chiral nematic liquid‐crystal electrolyte was polymerized by application of a voltage to yield a thin film. Circular dichroism measurements indicated a Cotton effect for the film. Optical texture suggests that the polymer shows a finger‐print texture and a spiral texture similar to that of the chiral nematic phase. This simple method provides a new technique for preparing chiral conducting films in a thermotropic chiral liquid‐crystal field.

Optical micrograph of (R)‐PEDOT* (no polarizer).     

Electrochemical Behaviour and Rapid Determination of L‐Dopa at Electrochemically Pretreated Screen Printed Carbon Electrode

A simple and rapid voltammetric method based on a disposable electrochemically pretreated screen‐printed carbon electrode is proposed for the determination of L ‐dopa. Under optimum differential pulse voltammetry conditions a limit of detection of 3.6×10^?7 M for L ‐dopa was obtained. The method was successfully applied to the determination of L ‐dopa in a commercial pharmaceutical formulation.     

Label‐Free Electrochemical Aptasensor for Determination of Chloramphenicol Based on Gold Nanocubes‐Modified Screen‐Printed Gold Electrode

An ultrasensitive label‐free electrochemical aptasensor was developed for selective detection of chloramphenicol (CAP). The aptasensor was made using screen‐printed gold electrode modified with synthesized gold nanocube/cysteine. The interactions of CAP with aptamer were studied by cyclic voltammetry, square wave voltammetry (SWV) and electrochemical impedance spectroscopy. Under optimized conditions, two linear calibration curves were obtained for CAP determination using SWV technique, from 0.03 to 0.10 µM and 0.25–6.0 µM with a detection limit of 4.0 nM. The aptasensor has the advantages of good selectivity and stability and applied to the determination of CAP in human blood serum sample.     

Electrochemical Characterization of Screen‐Printed Carbon Electrodes by Modification with Chitosan Oligomers

The kinetics on the current amplification of the disposable screen‐printed carbon electrodes (SPCEs) by modification with chitosan oligomers (COs), coupled with the Fe(CN) redox system, were characterized with the variation of electron‐transfer rate constant (k°) and the electroactive area (A_ea) at electrode surface. The nonlinear response characteristics of peak currents with increase in Fe(CN) bulk concentrations complicated the estimation of A_ea in cyclic voltammetric analysis. Upon the modification with COs, the rate constant of SPCEs was not much influenced and the current amplification was characterized with the increase of a better estimated A_ea, obtained from electrochemical impedance measurements and verified with the reciprocal of electron‐transfer resistances linearly proportional to the Fe(CN) bulk concentrations. It is hereby provided for an evaluation of the carbon based electrodes with modification.     

Sensitive Determination of Nitrofurantoin by Flow Injection Analysis Using Carbon Nanofiber Screen Printed Electrodes

In this work, a new method to quantify nitrofurantoin in aqueous media using a flow injection system connected to commercially available screen‐printed carbon nanofibers was developed. A pretreatment of the screen‐printed carbon nanofibers electrode with Britton? Robinson buffer/N,N‐dimethylformamide was applied to enhance the nitrofurantoin peak current signal in one step. The developed method was demonstrated to be sensible, reproducible, easy, and inexpensive. With a low detection limit, it is applicable to real samples. The results indicate that it is highly applicable for the detection of nitrofurantoin in several matrices. When urine samples without any pretreatment were analyzed, the method proved reproducible and sensible and had a low detection limit. The use of screen‐printed electrodes has advantages over other modified electrodes as a glassy carbon due to its versatility.     

A Novel L‐Cysteine Electrochemical Sensor Using Sulfonated Graphene‐poly(3,4‐Ethylenedioxythiophene) Composite Film Decorated with Gold Nanoparticles

By exploiting the electrostatic interaction between positively charged 3,4‐ethylenedioxythiophene cation radicals and negatively charged sulfonated graphene (SG) sheets, we prepared a poly(3,4‐ethylenedioxythiophene)‐sulfonated graphene (SG‐PEDOT) composite film by a one‐step electrochemical process. The composite was further decorated with gold nanoparticles (AuNPs) and employed as an electrode material for the detection of L ‐cysteine (Cys). The SG‐PEDOT composite film is shown to provide a rough surface for the electrodeposition of AuNPs and to improve substrate accessibility and interaction with Cys. Moreover, the AuNPs‐decorated composite exhibits better electrocatalytic performance than that of a SG‐PEDOT composite only. Under optimum experimental conditions, the amperometric current of the sensor is linearly related to the concentration of Cys in the 0.1 to 382 µM range, and the detection limit is 0.02 µM (at S/N=3). The modified electrode displays favorable selectivity, good stability and high reproducibility. The method was successfully applied to the detection of Cys in spiked human urine.     

Novel Preparation and Photoelectrochemical Properties of γ‐CuI Semiconductor Nanocrystallites on Screen‐Printed Carbon Electrodes

Cuprous iodide (γ‐CuI) is an important semiconductor material having a bang gap of 3.1 eV often used for visible light assisted photoelectrochemical and solar energy conservation systems. We report the first and unique preparation of fine and precisely controlled γ‐CuI semiconductor nanocrystallites on the surface of a screen‐printed carbon electrode using a photoelectrochemical copper nanoparticle deposition method with tris(hydroxymethyl)aminomethane (Tris) buffer solution as a control medium. Tris buffer helps to split Cu O and Cu^IIO oxidation states through specific complexation mechanism and in turn to selective iodination of Cu O to the formation of γ‐CuI on the electrode. Stable and linear photoelectrochemical response was further demonstrated against variable light intensity up to 400 Klux using the γ‐CuI modified system.     

Electrocatalytic Reduction and Determination of Dissolved Oxygen at a Preanodized Screen‐Printed Carbon Electrode Modified with Palladium Nanoparticles

Efficient and stable electrocatalytic activity for the reduction of O₂ at activated screen‐printed carbon electrodes modified with palladium nanoparticles (SPE*‐Pd) was demonstrated in this study. X‐ray photoelectron spectroscopy confirmed the formation of >C?O functional group on electrode surface during the preanodization procedure at 2.0 V (vs. Ag/AgCl). The existence of chloride moieties was also identified possibly from the organic binder of carbon ink used in SPE fabrication. Both >C?O and chloride functional groups were essential for the excellent stability of the SPE*‐Pd. Electrochemical impedance spectroscopy verified the enhanced kinetic rate of oxygen reduction reaction at the as‐prepared Pd nanoparticles. The SPE*‐Pd showed ca. 250 mV positive shift in peak potential together with twice increase in peak current compared to those observed at a SPE‐Pt. The calibration plot was linear up to 8 ppm of DO with sensitivity and regression coefficient of 4.49 μA/ppm and 0.9936, respectively. The variation coefficient of i_pc for 7 DO determinations with O₂‐saturated pH 7.4 PBS was 2.1%. Real sample assays for ground and tap waters gave consistent values to those measured by a commercial dissolved oxygen meter.     

Room temperature polymerization of poly(3,4‐ethylenedioxythiophene) as transparent counter electrodes for dye‐sensitized solar cells

Poly(3,4‐ethylenedioxythiophene) (PEDOT) counter electrode is prepared with in situ polymerization of 3,4‐ethylenedioxythiophene on a fluorine‐doped tin oxide over‐layer glass at room temperature. The cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization are measured to evaluate the catalytic activity of PEDOT counter electrode for I₃^?/I^? redox couple. Comparing the data with that of traditional thermal decomposed Pt counter electrode, it is found that PEDOT has higher catalytic activity than that of Pt counterpart. Power conversion efficiency of the dye‐sensitized solar cell (DSC) with PEDOT counter electrode can attain to 7.713%, a little higher than that of the cell with Pt counter electrode (7.300%). Taking the advantage of high transparency of PEDOT counter electrode, an Ag mirror is put on the back side of PEDOT counter electrode of the DSC to reflect light back for power conversion. Power conversion efficiency of the DSC with this special structure can be further enhanced to 8.359%, which mainly stems from the improved short‐circuit current density by the increased irradiated light intensity. Copyright © 2014 John Wiley & Sons, Ltd.     

对乙酰氨基酚在聚刚果红修饰电极上的伏安测定

应用循环伏安法于玻碳电极修饰聚刚果红薄膜,并研究对乙酰氨基酚(ACOP)在该修饰电极上的电化学行为.实验表明,聚刚果红修饰电极对ACOP具有良好的电催化性能.在2.0×10-7~2.0×10-6mol.L-1ACOP浓度范围内,其差示脉冲伏安峰电流随浓度变化呈良好的线性关系,检测限为4.0×10-8mol.L-1.该法可用于实际样品的含量测定.