Pyrolytic carbon film electrodes

Home-made pyrolytic carbon film electrodes (PCFE) were tested in voltammetric experiments. Different drugs were analyzed by differential pulse voltammetry. In many cases the reproducibility of the signals is as satisfactory as by using glassy carbon electrodes (GCE). The cleaning procedure is very easy to accomplish by wiping off the electrode surface with a paper tissue dipped into methanol. The peak- to residual current rate is much better at the PCFE than at the GCE. Therefore the detection limit is lowered at the former.     

碳纳米管负载铂修饰玻碳电极用于电化学发光的研究及其对富马酸酮替芬的测定

在玻碳电极上制备了碳纳米管负载纳米铂修饰电极(Pt-MWCNTs/GCE)。考察了联吡啶钌和富马酸酮替芬在3个不同电极上的电化学及其发光行为,并对其进行了对比。结果表明,在Pt-MWCNTs/GCE上富马酸酮替芬对联吡啶钌的电化学发光强度有明显的增敏作用,其增敏效果约为MWCNTs/GCE电极的2倍,约为裸玻碳电极的3.5倍,据此,建立了一种Pt-MWCNTs/GCE电极上电化学发光法检测富马酸酮替芬的新方法。在优化实验条件下,富马酸酮替芬的浓度在1.0×10-7～1.0×10-4mol/L范围内与其相对发光强度呈线性关系,线性回归方程为I=48.805×106c+221.03(r=0.9969),检出限为2.4×10-9mol/L,连续平行测定1.0×10-5mol/L的富马酸酮替芬溶液5次,发光强度的RSD为3.3%。对样品进行回收率实验,回收率为99%～104%,RSD为2.1%。     

Glassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in Polylysine

We report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT‐Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0 mg/mL MWCNT in 1.0 mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT‐Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self‐assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self‐assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT‐Plys as polycationic layers for further adsorption of GOx is also evaluated.     

电聚合烟酰胺制备电化学传感器：同时测定多巴胺、尿酸和抗坏血酸

用循环伏安法（CV）选择不同电位区间来电聚合烟酰胺（NA）得到了两种聚合物膜修饰电极：poly-niacinamide/GCE (poly-NA/GCE)和poly- nicotinic acid /GCE (poly-NC/GCE)。这两电极都具有显著电化学催化作用,能明显地降低多巴胺（DA）、尿酸（UA）和抗坏血酸(AA)的氧化过电位,并在混合溶液中使这些物质的氧化峰电位距离足够大,可进行三物质的同时测定。poly-NC/GCE的电催化性能更好一些,用差分脉冲伏安法（DPV）测定抗坏血酸,线性范围为75–3000 µmol L-1,电流灵敏度为5.6 mA•L•mol-1;测定多巴胺,线性范围为0.37 – 16 µmol L-1,电流灵敏度为1140 mA•L•mol-1; 测定尿酸,线性范围为0.74 – 230 µmol L-1,电流灵敏度为102 mA•L•mol-1。该电极具有很高的灵敏度、选择性和抗污染能力。     

Au/GCE电极对水中15种苯酚衍生物的测定

研究了15种不同取代基苯酚衍生物在纳米金/玻碳 (Au/GCE) 电极上的电化学响应. 测试表明：该电极对15种苯酚衍生物的电化学反应各呈现出不同程度的电催化作用;与GCE和平面金电极相比,苯酚衍生物的氧化峰电流均有所增加,氧化电位受待测物反应活性影响较大;水杨酸在Au/GCE电极上响应迅速,电流灵敏度是GCE电极的1.8倍;该电极可用于多种苯酚衍生物的痕量测定.     

Simple immobilization of pyrroloquinoline quinone on few-walled carbon nanotubes

Pyrroloquinoline quinone (PQQ) was immobilized on glassy-carbon electrodes (GCE) modified with single-walled carbon nanotubes (SWCNT), few-walled carbon nanotubes (FWCNT) and carbon black (Vulcan XC72R). Modified electrodes were prepared by drop-casting. Immobilization was achieved with an extremely simple dipping procedure and without any further modification to the electrodes. Electrochemical performance of the electrodes was studied by cyclic voltammetry and spectroelectrochemistry. FWCNT adsorbed 30 times more PQQ than the other carbon materials. Compared to more complicated immobilization methods, PQQ/FWCNT/GCE showed well-defined electrochemistry in a considerably wide pH area from 2 to 12. The dipping process is affected by pH and electrostatic forces. At dipping pH 9.5, where both FWCNTs and PQQ have strong negative charge, the adsorption was halved compared to dipping pH 2, where the charges are smaller.     

Carbon‐Based Electrodes for Sensitive Electroanalytical Determination of Aminonaphthalenes

The electroanalytical performance of bare glassy carbon electrodes (GCE) for the determination of 1‐aminonaphthalene (1‐AN) and 2‐aminonaphthalene (2‐AN) was compared with GCE modified by a Nafion permselective membrane or multiwalled carbon nanotubes and with other types of carbon‐based materials, carbon film and boron doped diamond. Nafion‐modified GCE gave the highest sensitivity and lowest detection limit (0.4 µmol L^?1) for differential pulse voltammetric determination of 1‐AN. Electrochemical impedance spectroscopy gave information about the processes at the electrode surface. Simultaneous determination of 1‐AN and 2‐AN in a mixture at GCE and their determination in model samples of river water is presented.     

Voltammetric detection of synthetic water-soluble phenolic antioxidants using carbon nanotube based electrodes

Glassy carbon electrodes (GCE) modified with carbon nanotubes (CNT) have been created for detection of phenolic compounds—one of the important group of antioxidants in life sciences. The surface of electrode has been characterized by atomic force microscopy. The presence of CNT leads to an at least 20-fold increase in the surface roughness of the electrode. The CNT layer displays closely intertwined vermicular structures with high degree of homogeneity at CNT suspension concentration of 0.2–0.5 mg L⁻¹. Synthetic water-soluble antioxidants (hydroquinone, catechol, pyrogallol, and their derivatives) are electrochemically active on bare GCE and CNT-modified GCE in phosphate buffer solution pH 7.4. Effect of substitutes in molecular structure of phenolic antioxidants has been evaluated. In several cases, oxidation at CNT-modified GCE occurs at potentials that are less positive by 100–200 mV in comparison to bare GCE. The electrodes were studied with respect to their capability of phenols voltammetric sensing. CNT-modified GCE display an enlarged linear range in the calibration graphs and lower detection limits. Voltammetric method for determination of hydroquinone, catechol, pyrogallol, and their derivatives has been developed.     

Electroanalytical method for determination of shikonin based on the enhancement effect of cyclodextrin functionalized carbon nanotubes

A simple and sensitive electroanalytical method for determination of shikonin,a widely used antitumoral agent,using β-cyclodextrin-functionalized multiwalled carbon nanotubes composite modified glassy carbon electrodes(MWCNTs/β-CD/GCE) was presented.CDs are water-soluble and environmentally friendly and can improve the dispersibility of MWCNTs/β-CD functional materials,which was confirmed by SEM.The electrochemical behaviors of shikonin on different electrodes were investigated by cyclic voltammetry(CV) and differential pulse voltammograms(DPVs).The results demonstrated that the redox peak currents of shikonin obtained at MWCNTs/β-CD/GCE were much higher than those at theβ-CD/GCE and MWCNTs/GCE,which can be attributed to the combination of the excellent electrocatalytic properties of MWCNTs and the molecular recognition ability of β-CD.At MWCNTs/β-CD/GCE,the response current exhibits a linear range from 5.0 nmol/L to 10.0 μmol/L with a detection limit of 1.0 nmol/L(S/N = 3).As a practical application,the proposed method was applied to quantitatively determine shikoninin urine samples with satisfying results.     

Electrochemical Behavior and Voltammetric Determination of Curcumin at Electrochemically Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of curcumin by using a electrochemically reduced graphene oxide (ERGO) modified glass carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The electrochemical behaviors of curcumin at ERGO/GCE were investigated by cyclic voltammetry, suggesting that the ERGO/GCE exhibits excellent electrocatalytic activity towards curcumin, compared with bare GCE and GO/GCE electrodes. The electrochemical reaction mechanisms of curcumin, demethoxycurcumin and bisdemethoxycurcumin at the ERGO/GCE were also investigated and discussed systematically. Under physiological condition, the modified electrode showed linear voltammetric response from 0.2 μM to 60.0 μM for curcumin, with the detection limit of 0.1 μm. This work demonstrates that the graphene‐modified electrode is a promising strategy for electrochemical determination of biological important phenolic compounds.     

Lead ion sensor with electrodes modified by imidazole-functionalized polyaniline

Glassy carbon electrodes (GCE) and carbon paste electrodes (CPE) were modified with imidazole functionalized polyaniline with the aim to develop a sensor for lead (II) in both acidic and basic aqueous solution. The electrodes were characterized by cyclic voltammetry and differential pulse adsorptive stripping voltammetry. The limit of detections obtained with glassy carbon electrode and carbon paste electrode are 20?ng?mL^-1 and 2?ng?mL^-1 of lead ion, respectively. An interference study was carried out with Cd(II), As(III), Hg(II) and Co(II) ions. Cd(II) ions interfere significantly (peak overlap) and As(III) has a depressing effect on the lead signal. The influence of pH was investigated indicating that bare and modified GCE and CPE show optimum response at pH?4.0 ± 0.05.

Behavior of Palladium Nanoparticles in the Absence or Presence of Cobalt Tetraaminophthalocyanine for the Electrooxidation of Hydrazine

We report on the electrodeposition of palladium nanoparticles (PdNPs) on a glassy carbon electrode (GCE) and onto a poly‐CoTAPc‐GCE (CoTAPc=cobalt tetraamino phthalocyanine) surface. The electrodes are denoted as PdNPs‐GCE and PdNPs/poly‐CoTAPc‐GCE, respectively. PdNPs/poly‐CoTAPc‐GCE showed the best activity for the oxidation of hydrazine at the lowest potential of ?0.28 V and with the highest currents. The results were further supported by electrochemical impedance spectroscopy (EIS) which showed that there was less resistance to charge transfer for PdNPs/poly‐CoTAPc‐GCE compared to PdNPs‐GCE. The catalytic rate constant for hydrazine oxidation was 6.12×10⁸ cm³ mol^?1 s^?1 using PdNPs/poly‐CoTAPc‐GCE.     

Single‐Wall Carbon Nanotubes Covalently Functionalized with Polylysine: Synthesis,Characterization and Analytical Applications for the Development of Electrochemical (Bio)Sensors

This work reports the synthesis of single‐wall carbon nanotubes (SWCNT) covalently functionalized with polylysine (Plys) and the analytical performance of glassy carbon electrodes (GCE) modified with this material (GCE/SWCNT‐Plys). The resulting electrodes showed an important decrease in the overvoltages for the oxidation of ascorbic acid, uric acid and hydrogen peroxide as well as for the reduction of hydrogen peroxide. The favorable interaction of glucose oxidase (GOx) with SWCNT‐Plys allowed the sensitive and selective glucose biosensing at ?0.100 V without any permselective membrane. The proposed sensor was challenged with different real samples without pretreatment showing an excellent correlation with the reported values.     

Electrode Modification through Click Chemistry Using Ni and Co Alkyne Phthalocyanines for Electrocatalytic Detection of Hydrazine

This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5‐hexyn‐oxy) cobalt(II) phthalocyanine (complex 2 ) and tetrakis(5‐hexyn‐oxy) nickel(II) phthalocyanine (complex 3 ) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3‐dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP 2 ‐clicked‐GCE and NiP 3 ‐clicked‐GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc‐GCE was 6.09 μM, while the NiPc‐GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM⁻¹ for the CoPc‐GCE and 111.2 μA mM⁻¹ for the NiPc‐GCE.     

基于氧化锌/碳纳米纤维材料的氧氟沙星电化学传感器的构建及应用

通过静电纺丝技术合成碳纳米纤维,以循环伏安法在此碳纤维上电聚合乙酸锌制备复合纳米材料作为一种新型的电化学增敏剂,用于修饰玻碳电极,开发了一种基于碳纤维和氧化锌复合材料的新型电化学传感器(ZnO/CNF/GCE)。使用循环伏安法、差分脉冲伏安法等进行电化学催化性能的研究,并优化实验条件。结果表明,与裸电极相比,在pH 5.5磷酸盐缓冲溶液中,ZnO/CNF/GCE修饰电极能使氧氟沙星的峰电流明显提升,线性范围1~200μmol/L,检测限为0.33μmol/L。该ZnO/CNF/GCE修饰电极已用于氧氟沙星滴耳液中氧氟沙星的含量测定。     

Adsorption phenomena in the NAD+/NADH system at glassy carbon electrodes

A variety of electrochemical approaches has been used to investigate the adsorption of NAD⁺, NADH and the NAD-NAD dimer from aqueous solution at glassy carbon electrodes (GCE) with supplementary studies of adsorption at pyrolytic graphite and platinum electrodes from aqueous media and at GCE from DMSO solution. The following hypotheses are advanced concerning the adsorption orientation: at carbon electrodes, on which NADH is not adsorbed, NAD⁺ produced by anodic oxidation of the NADH is first rapidly adsorbed in a planar configuration relative to the electrode surface, which is probably bound to the surface through the adenine moiety; there is then a relatively slow reorientation of the adsorbed NADH molecules to a perpendicular orientation relative to the electrode surface, which adsorbate is more tightly bound to the surface than the planar oriented adsorbate and which likely involves interaction between parallel adenine and pyridinium rings. Reduction (one-electron process) of NAD⁺ at the GCE produces the NAD-NAD dimer, which, at a clean electrode surface, involves a diffusion-controlled process and an adsorption-controlled process; the latter is due to formation of adsorbed dimer, which is more strongly adsorbed than NAD⁺. The dimer is oxidized at the GCE only if it is adsorbed. The factors controlling and involved in the adsorption processes have been examined with particular reference to the use of anodic voltammetry for the analytical determination of NADH.     

Electrochemical Sensor for the Quantification of Dopamine Using Glassy Carbon Electrodes Modified with Single‐Wall Carbon Nanotubes Covalently Functionalized with Polylysine

We report a dopamine electrochemical sensor based on the modification of glassy carbon electrodes (GCE) with polylysine‐functionalized single‐wall carbon nanotubes (SWCNT‐PLys). The resulting electrodes (GCE/SWCNT‐PLys) showed a significant improvement in the electrooxidation of dopamine with drastic decrease in the peak potentials separation and important enhancement in the associated currents. Dopamine was detected by differential pulse voltammetry‐adsorptive stripping with medium exchange at nanomolar levels even in the presence of high excess of ascorbic and uric acids. The sensor was successfully used for the quantification of dopamine in urine samples enriched with the neurotransmitter.     

用稀土(镱)杂多酸盐/多壁碳纳米管修饰的玻碳电极测定亚硝酸根

将多壁碳纳米管分散在镱(Ⅲ)杂多酸盐溶液中,将上述获得的悬浊液滴涂在玻碳电极表面,制备了镱(Ⅲ)杂多酸盐/多壁碳纳米管修饰的玻碳电极(YbHS-MWCNT′s/GCE)。采用交流阻抗法对电极表面的性能进行了表征,采用循环伏安法对其电化学性能进行研究。研究发现,亚硝酸根在该修饰电极上出现一个氧化峰,氧化峰电位在-0.45V处,提出了用循环伏安法测定亚硝酸根的方法。亚硝酸根的浓度在5.0×10-6～1.0×10-4mol.L-1范围内,氧化峰电流与其浓度呈线性关系。修饰电极用于环境水样中亚硝酸根离子的测定,回收率在97.2%～98.0%之间。     

Characterization of DNA Layers Adsorbed on Glassy Carbon Electrodes

A DNA layer adsorbed at glassy carbon electrodes (GCE) was characterized by ellipsometry, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The presence of the adsorbed DNA layer on polished glassy carbon electrodes was assessed indirectly by ellipsometric measurements. Ellipsometry was also useful to evaluate the influence of the oxide layer formed on glassy carbon electrodes, either spontaneously or after electrochemical pretreatments, on the DNA adsorption and further electrooxidation process. SEM and AFM images of the electrode surface covered by a thick layer of DNA reveal a nonuniform distribution, leaving channels and islands of the biological material.     

Sensitive Voltammetric Determination of Baicalein at Thermally Reduced Graphene Oxide Modified Glassy Carbon Electrode

This work presents a sensitive voltammetric method for determination of the flavonoid baicalein by using a thermally reduced graphene oxide (TRGO) modified glassy carbon electrode (GCE) in 100 mM KCl‐10 mM sodium phosphate buffer solution (pH 7.40). The surface morphology and structure of TRGO investigated by atomic force microscopy, FT‐IR spectroscopy and Raman spectroscopy reveal that the TRGO prepared maintained as single or bilayer sheets and with significant edge‐plane‐like defect sites. The TRGO/GCE modified electrode shows more favorable electron transfer kinetics for potassium ferricyanide and potassium ferrocyanide probe molecules, which are important electroactive compounds, compared with bare GCE and GO/GCE electrodes. The electrochemical behaviors of baicalein at the TRGO/GCE were investigated by cyclic voltammetry, suggesting that the TRGO/GCE exhibits excellent electrocatalytic activity to baicalein. Under physiological conditions, the modified electrode showed linear voltammetric response from 10 nM to 10 µM for baicalein, with a detection limit of 6.0 nM. This work demonstrates that the graphene‐modified electrode is a promising tool for electrochemical determination of flavonoid drugs.