Glassy carbon electrode modified with poly-Neutral Red for photoelectrocatalytic oxidation of NADH

A new approach is described for the photoelectrocatalytic oxidation of Reduced ß-Nicotinamide Adenine Dinucleotide (NADH). It is based on a glassy carbon electrode (GCE) modified with a film of poly-Neutral Red (poly-NR) that is obtained by electropolymerization. Electrochemical measurements revealed that the modified electrode displays electrocatalytic and photo-electrocatalytic activity towards oxidation of NADH. If irradiated with a 250-W halogen lamp, the electrode yields a strongly increased electrocatalytic current compared to the current without irradiation. Amperometric and photo-amperometric detection of NADH was performed at +150 mV vs. Ag/AgCl/KCl_sat and the currents obtained are linearly related to the concentration of NADH. Linear calibration plots are obtained in the concentration range from 1.0 μM to 1.0 mM for both methods. However, the slope of the current-NADH concentration curve of the photo-electrocatalytic procedure was 2-times better than that obtained without irradiation.

Simultaneous determination of levodopa, NADH, and tryptophan using carbon paste electrode modified with carbon nanotubes and ferrocenedicarboxylic acid

The redox response of a modified carbon nanotube paste electrode of ferrocenedicarboxylic acid was investigated. Cyclic voltammetry, differential pulse voltammetry, and chronoamperometry were used to investigate the electrochemical behavior of levodopa (LD) at modified electrode. Under the optimized conditions (pH 5.0), the modified electrode showed high electrocatalytic activity toward LD oxidation; the overpotential for the oxidation of LD was decreased by more than 190 mV, and the corresponding peak current increased significantly. Differential pulse voltammetric peak currents of LD increased linearly with its concentrations at the range of 0.04 to 1,100 μM, and the detection limit (3σ) was determined to be 12 nM. The diffusion coefficient ( D = 9.2 ×10 ^{- 6}cm²/s ) \left( {D = {9}.{2} \times {1}{0^{ - {6}}}{\hbox{c}}{{\hbox{m}}^2}/{\hbox{s}}} \right) and transfer coefficient (α = 0.49) of LD were also determined. Mixture of LD, NADH, and tryptophan (TRP) can be separated from one another by differential pulse voltammetry. These conditions are sufficient to allow determination of LD, NADH, and TRP both individually and simultaneously. The modified electrode showed good reproducibility, remarkable long-term stability, and especially good surface renewability by simple mechanical polishing. The results showed that this electrode could be used as an electrochemical sensor for determination of LD, NADH, and TRP in real samples such as urine and water samples.     

磺胺在碳纳米管修饰玻碳电极上的电化学行为

磺胺类抗菌药是一类允许在饲料中添加的兽用广谱抗菌药.它被广泛用于治疗家畜呼吸道、消化道细菌感染、猪萎缩性鼻炎、禽霍乱、伤寒等疾病[1].停药期用药或用药不当将导致动物食品中抗菌药残留超标.人们长期食用含磺胺类抗菌药残留超标的动物产品,将导致肝肾损伤和体内耐药菌株产生,危害到人们的身体健康和疾病治疗.     

嵌入式碳纳米管石墨电极测定灯盏花素的研究

制备嵌入式多壁碳纳米管修饰石墨电极,利用循环伏安法(CV)研究灯盏花素在嵌入式多壁碳纳米管修饰石墨电极(ESCFE)上的电化学氧化行为,结果表明,灯盏花素在修饰电极上出现一对明显的准可逆氧化还原峰,峰电位分别为Epa=0.17 V和Epc=0.05 V(△E=0.12 V),峰电流分别为ipa=42.79μA,ipc=...     

Application of multi-walled carbon nanotubes modified carbon ionic liquid electrode for electrocatalytic oxidation of dopamine

A simple, sensitive, and reliable method based on a multi-walled carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (CILE) has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The acid-treated MWNTs with carboxylic acid functional groups could promote the electron-transfer reaction of DA and inhibit the voltammetric response of AA. Due to the good performance of the ionic liquid, the electrochemical response of DA on the MWNTs/CILE was better than that of other MWNTs modified electrodes. Under the optimum conditions a linear calibration plot was obtained in the range 5.0×10(-8) to 2.0×10(-4) mol L(-1) and the detection limit was 1.0×10(-8) mol L(-1).     

Amperometric glucose biosensor based on boron-doped carbon nanotubes modified electrode

Doped carbon nanotubes are now extremely attractive and important nanomaterials in bioanalytical applications due to their unique physicochemical properties. In this paper, the boron-doped carbon nanotubes (BCNTs) were used in amperometric biosensors. It has been found that the electrocatalytic activity of the BCNTs modified glassy carbon (GC) electrode toward the oxidation of hydrogen peroxide is much higher than that of the un-doped CNTs modified electrode due to the large amount of edge sites and oxygen-rich groups located at the defective sites induced by boron doping. Glucose oxidase (GOD) was selected as the model enzyme and immobilized on the BCNTs modified glassy carbon electrode by entrapping GOD into poly(o-aminophenol) film. The performance of the sensor was investigated by electrochemical methods. At an optimum potential of +0.60 V and pH 7.0, the biosensor exhibits good characteristics, such as high sensitivity (171.2 nA mM(-1)), low detection limit (3.6 microM), short response time (within 6s), satisfactory anti-interference ability and good stability. The apparent Michaelis-Menten constant (K(m)(app)) is 15.19 mM. The applicability to the whole blood analysis of the enzyme electrode was also evaluated.     

Boron-doped carbon nanotubes serving as a novel chemical sensor for formaldehyde

To search for a novel sensor to detect the presence of formaldehyde (HCOH), we investigate reactivities of the intrinsic and boron-doped (B-doped) single-walled (8, 0) carbon nanotube (SWCNT) with HCOH using density functional theory calculations. Compared with the intrinsic SWCNT, the B-doped SWCNT presents high sensitivity to HCOH. This is attributed to the strongly chemical interaction between the electron-rich oxygen atom of HCOH and the electron-scarce boron atom of the doped SWCNT. B-doped SWCNTs are expected to be a potential candidate for detecting the presence of HCOH.     

Surface-enhanced Raman scattering of single-walled carbon nanotubes on modified silver electrode

A roughed silver electrode modified with gold/silver nanoparticles is used as a substrate, on which high quality SERS of SWCNTs are obtained, indicating that the modified silver electrode is a high-quality SERS-active substrate for SWCNTs. Some new bands that indicate the structure of SWCNTs were obtained. The gold/silver nanoparticles modified on the roughed silver electrode surface can not only make sure the strong adsorption of SWCNTs in this system but also play an important role in magnifying the surface local electric field near the silver electrode surface through resonant surface plasmon excitation. From the rich information on the modified silver electrode obtained from the SERS and the potential dependent SERS, we may deduce the probable SERS mechanism in the process. The theory and experiment results indicate that it is can be used as a new technique for monitoring synthesis quality of SWCNTs. The probable reasons are given.     

Enhanced sensing of anthraquinone dyes using multiwalled carbon nanotubes modified electrode

The voltammetric behaviour of two anthraquinone dyes such as Alizarin Red S (ARS) and Reactive blue 4 (RB4) was investigated at plain glassy carbon electrode (GCE), multiwalled carbon nano tube modified GCE (MWCNT/GCE) and zeolite modified GCE (ZE/GCE) using cyclic voltammetry. Effects of pH, scan rate and concentration were studied. The surface morphology of the modified electrode in the absence and presence of dye molecules was characterized by scanning electron microscopy (SEM). A systematic study on the variation of experimental parameters with differential pulse stripping voltammetry (DPSV) was carried out and the optimized experimental conditions were arrived. MWCNT/GCE performed well among the three electrode systems and the limit of detection (LOD) was 0.036?µg?mL^?1 for ARS and 0.05?µg?mL^?1 for RB4 on this modified system. Suitability of the differential pulse stripping voltammetric method for the trace determination of textile dyes in effluents was also realized.     

Disposable screen-printed bismuth electrode modified with multi-walled carbon nanotubes for electrochemical stripping measurements

Integrating the advantages of screen printing technology with the encouraging electroanalytical characteristic of metallic bismuth, we developed an ultrasensitive and disposable screen-printed bismuth electrode (SPBE) modified with multi-walled carbon nanotubes (MWCNTs) for electrochemical stripping measurements. Metallic bismuth powders and MWCNTs were homogeneously mixed with graphite-carbon ink to mass-prepare screen-printed bismuth electrode doped with multi-walled carbon nanotubes (SPBE/MWCNT). The electroanalytical performance of the prepared SPBE/MWCNT was intensively evaluated by measuring trace Hg(II) with square-wave anodic stripping voltammetry (SWASV). The results indicated that the SPBE modified with 2 wt% MWCNTs could offer a more sensitive response to trace Hg(II) than the bare SPBE. The stripping current obtained at SPBE/MWCNT was linear with Hg(II) concentration in the range from 0.2 to 40 μg/L (R(2) = 0.9976), with a detection limit of 0.09 μg/L (S/N = 3) under 180 s accumulation. The proposed "mercury-free" electrode, with extremely simple preparation and ultrahigh sensitivity, holds wide application prospects in both environmental and industrial monitoring.     

Benzoquinone modified electrode for sensing NADH and ascorbic acid

A benzoquinone modified basal plane pyrolytic graphite electrode shows electrocatalytic activity for the oxidation of NADH and ascorbic acid in phosphate buffer (pH 7.3). The modified electrode shows a linear variation of catalytic current with concentration in the range 1-10 mM for both NADH and ascorbic acid. The rate constants have been estimated from the surface coverage data.     

Tetracyanoquinodimethane (TCNQ) modified electrode for NADH oxidation

A TCNQ-modified edge-plane pyrolytic graphite electrode prepared by a dip-coating procedure shows electrocatalytic activity for NADH oxidation in phosphate buffer solutions (pH 7.0). The modified electrode is stable and shows a linear relation for NADH in the concentration range 1–10 mM. The rate constant between adsorbed TCNQ and NADH in solution has been estimated to be 1.46 × 10⁶ M⁻¹s⁻¹ at 25°C. The modified electrode has the potential use as a sensor for dehydrogenase-enzyme-based substrates.     

pharmaceutical and biological samples using modified multiwall carbon nanotubes paste electrode

A carbon paste electrode(CPE) chemically modified with multiwall carbon nanotubes and ferrocene(FC) was used as a selective electrochemical sensor for the simultaneous determination of trace amounts of cysteamine(CA) and folic acid(FA).This modified electrode showed very efficient electrocatalytic activity for the anodic oxidation of CA.The peak current of differential pulse voltammograms of CA and FA increased linearly with their concentration in the ranges of 0.7-200μmol/L CA and 5.0- 700μmol/L FA.The detection limits for CA and FA were 0.3μmol/L and 2.0μmoI/L,respectively.The diffusion coefficient(D) and transfer coefficient(α) of CA were also determined.These conditions are sufficient to allow determination of CA and FA both individually and simultaneously.     

Quantification of methyldopa in pharmaceuticals using a glassy carbon electrode modified with carbon nanotubes

The quantification of methyldopa in pharmaceuticals has been carried out using a glassy carbon electrode(GCE) modified with multi-walled carbon nanotubes(MWCNTs). Methyldopa exhibited a quasi-reversible response with a peak potential separation of 473 m V on a bare GCE. However, the cyclic voltammetric behaviour of methyldopa was improved with the increase of the amount of MWCNTs. It was also shown that the electrocatalytic activity of the electrode towards the response of methyldopa was higher with larger amount of film on the surface. The results showed that the peak current was proportional to the concentration of methyldopa with a linear dynamic range of 0.005–0.388 mmol/L and a detection limit of 1.0 nmol/L was obtained using square wave voltammetry. The experimental data showed that the detection limit of methyldopa and peak separation from interfering compounds such as ascorbic acid(AA) and uric acid(UA) were improved using the proposed procedure. The method was successfully applied for the determination of methyldopa in pharmaceuticals.