Gold Nanoparticles‐β‐Cyclodextrin‐Chitosan‐Graphene Modified Glassy Carbon Electrode for Ultrasensitive Detection of Dopamine and Uric Acid

The nanocomposite (denoted as GR‐AuNPs‐CD‐CS) of graphene (GR), gold nanoparticles (AuNPs), chitosan (CS) and β‐cyclodextrin (β‐CD) was prepared to modify a glassy carbon electrode. The as‐modified electrode was explored for the ultrasensitive detection of dopamine (DA) and uric acid (UA). The modified electrode demonstrated linearly increased current response in the concentration range of 0.1–120 µm for DA and 0.05–70 µm for UA, with so far the best detection limit for DA and UA. Good stability and repeatability were further demonstrated for the as‐made sensor.     

聚L-苏氨酸修饰电极对多巴胺和肾上腺素的电催化氧化

利用循环伏安法将L-苏氨酸聚合修饰在玻碳电极表面, 制成聚L-苏氨酸修饰电极. 实验表明, 该电极对多巴胺和肾上腺素都有较好的催化氧化效果. 运用循环伏安法详细研究了修饰电极的电化学性质. 在pH 2.5的磷酸盐缓冲溶液(PBS)中, 肾上腺素的电子传递系数为0.51, 表观反应速率常数为1.33 s-1; 在pH 7.5的PBS中, 多巴胺在电极上产生一对氧化还原峰, 多巴胺在电极上的电子传递系数为0.60, 表观反应速率常数为0.92 s-1. 该修饰电极对多巴胺和肾上腺素能够进行同时测定, 还原峰电流与多巴胺和肾上腺素浓度分别在1.0×10-6-5.0×10-4 mol·L-1和3.0×10-6-1.0×10-4 mol·L-1范围内呈现良好的线性关系.     

2,2‐Bis(3‐Amino‐4‐hydroxyphenyl)hexafluoropropane Modified Glassy Carbon Electrodes as Selective and Sensitive Voltammetric Sensors. Selective Detection of Dopamine and Uric Acid

2,2‐bis(3‐Amino‐4‐hydroxyphenyl)hexafluoropropane (BAHHFP) was electro‐polymerized oxidatively on glassy carbon by cyclic voltammetry. The activity of the modified electrode towards ascorbic acid (AA), uric acid (UA) and dopamine (DA) was characterized with cyclic voltammetry and differential puls voltammetry (DPV). The findings showed that the electrode modification drastically suppresses the response of AA and shifts it towards more negative potentials. Simultaneously an enhancement of reaction reversibility is seen for DA and UA. Unusual, selective preconcentration features are observed for DA when the polymer‐modified electrode is polarized at negative potential. In a ternary mixture containing the three analytes studied, three baseline resolved peaks are observed in DPV mode. At physiological pH 7.4, after 5 min preconcentration at ?300 mV, peaks positions were ?0.073, 0.131 and 0.280 V (vs. Ag/AgCl) for AA, DA and UA, respectively. Relative selectivities DA/AA and UA/AA were over 4000 : 1 and 700 : 1, respectively. DA response was linear in the range 0.05–3 μM with sensitivity of 138 μA μM^?1 cm^?2 and detection limit (3σ) of 5 nM. Sensitive quantification of UA was possible in acidic solution (pH 1.8). Under such conditions a very sharp peak appeared at 630 mV (DPV). The response was linear in the range 0.5–100 μM with sensitivity of 4.67 μA μM^?1 cm^?2 and detection limit (3σ) of 0.1 μM. Practical utility was illustrated by selective determination of UA in human urine.     

The Electrocatalytic Oxidation of Thymine at α‐Cyclodextrin Incorporated Carbon Nanotube‐Coated Electrode

Electrocatalytic oxidation of thymine at α‐cyclodextrin (α‐CD) incorporated carbon nanotube‐coated electrode (CNT/CE) was thoroughly studied in alkaline media. CNT showed an electrocatalytic effect on the oxidation of thymine, formation of a supramolecular inclusion complex between α‐CD and thymine at CNT/CE further enhanced the sensitivity to thymine. The electrocatalytic behavior was further developed as a sensitive detection scheme for thymine by differential pulse voltammetry. A linear calibration over the concentration range from 2.5×10^?5 to 1.8×10^?3 mol/L in pH 10.8 NaHCO₃‐Na₂CO₃ buffer solution was obtained with a detection limit of 5×10^?6 mol/L.     

Electrocatalytic Oxidation of Dopamine at Sol‐Gel Carbon Composite Electrode Chemically Modified with Copper Hexacyanoferrate

An organic‐inorganic composite electrode was prepared by the sol‐gel method. For this purpose the carbon composite electrode (CCE) was modified with copper hexacyanoferrate (CuHCF). The CuHCF‐CCE was prepared by two methods. In one method CCE was prepared in one step and in another method the electrode was prepared in a two‐step process. The electrochemical behavior of the CuHCF modified electrode was studied by cyclic voltammetry; the modified electrode shows a pair of peaks with a surface‐confined characteristic in a 0.1 M phosphate buffer (pH 7) with K⁺ cation, as a supporting electrolyte. The CuHCF‐CCE showed electrocatalytic activity toward oxidation of Dopamine (DA). The kinetics of the catalytic reaction was investigated by using chronoamperometry. The average value of the rate constant for catalytic reaction and the diffusion coefficient were calculated. At a 0.85 V potential under hydrodynamic conditions (stirred solution), the oxidation current is proportional to the dopamine concentration, and the calibration plot was linear over the concentration range of 5‐85 μM.     

Electrochemical Oxidation and Sensitive Determination of Acetaminophen in Pharmaceuticals at Poly(3,4‐ethylenedioxythiophene)‐Modified Screen‐Printed Electrodes

The current study reports electrocatalytic oxidation of acetaminophen at screen‐printed electrode (SPE) modified with electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film. Cyclic voltammetric studies show that the SPE/PEDOT electrode lowers overpotentials and improves electrochemical behavior of acetaminophen (ACAP) in aqueous buffer solutions, compared to the bare SPE. Excellent analytical features are achieved, including high sensitivity, low detection limit and satisfactory dynamic range, by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and flow‐injection amperometry (FIA) under optimized conditions. The proposed methods obtain satisfactory results in detection of acetaminophen in two commercial tablets.     

β‐Cyclodextrin‐Functionalized Gold Nanoparticles/Poly(L‐cysteine) Modified Glassy Carbon Electrode for Sensitive Determination of Metronidazole

A simple electrochemical method was developed to determine metronidazole based on β‐cyclodextrin‐functionalized gold nanoparticles/poly(L ‐cysteine) modified glassy carbon electrode (β‐CD‐GNPs/poly(L ‐cys)/GCE). The electropolymerized film of poly(L ‐cys) provides a stable matrix for the fabrication of a sensing interface. β‐CD‐GNPs can form inclusion complexes with metronidazole and act as a modifier with catalytic function. The modified electrode exhibited excellent electrocatalytic activity towards metronidazole. The reaction of metronidazole at the modified electrode was an irreversible process controlled by diffusion. Under optimum experimental conditions, the logarithm of catalytic currents shows a good linear relationship with that of the metronidazole concentration in the range of 0.1–600 µmol/L with a low detection limit of 14 nmol/L. In addition, the modified electrode exhibited satisfactory stability, sensitivity and reproducibility, and could be applied to the determination of metronidazole in an injection solution.     

Electrocatalytic and Analytical Response of β‐Cyclodextrin Incorporated Carbon Nanotubes‐Modified Electrodes Toward Guanine

The utility of β‐cyclodextrin incorporated carbon nanotubes‐modified electrodes (β‐CD/CNT/E) for electrocatalytic oxidation of guanine in aqueous solution is demonstrated. Compared to the conventional electrode, it lowers the overpotential and enhances the peak current significantly. The action mechanism of β‐CD/CNT/E was discussed systemically. The results demonstrated that the use of β‐CD/CNT/E clearly provides an effective methodology for the determination of guanine. Based on the signal of guanine, an estimate of DNA concentration can be recognized with a limit of detection of 10 ng mL^?1.     

Direct Simultaneous Determination of α‐ and β‐Naphthol Isomers at GC‐Electrode Modified with CNTs Network Joined by Pt Nanoparticles Through Derivative Voltammetry

The semi‐derivative technique was adopted to improve the resolution and surfactant was added to sample solution to enhance the sensitivity, α‐ and β‐naphthol isomers could be determined directly and simultaneously at glassy carbon electrode modified with carbon nanotubes network joined by Pt nanoparticles. In 0.1 mol L^?1 HAc‐NaAc buffer solution (pH 5.8), the linear calibration ranges were 1.0×10^?6 to 8.0×10^?4 mol L^?1 for both α‐ and β‐naphthols, with detection limits of 5.0×10^?7 for α‐ and 6.0×10^?7 mol L^?1 for β‐naphthol. The amount of naphthol isomers in artificial wastewater has been tested with above method, and the recovery was from 98% to 103%.     

基于两种复合纳米材料修饰的电极对多巴胺的催化氧化

本文先在Au电极表面自组装硫辛酰胺(T-NH_2),再利用电化学还原的方法将还原氧化石墨烯(ERGO)和纳米金(AuNPs)电沉积到T-NH_2表面,采用循环伏安法考察了电极的电化学性能。实验表明,该修饰电极对多巴胺(DA)具有良好的电催化作用,优化条件下,DA的氧化峰电流与其浓度在6.49×10~(-6)~7.62×10~(-3) mol/L范围内呈良好的线性关系(R=0.996),检出限为2.0×10~(-6) mol/L。     

Catalytic Au Electrodes Based on SAMs of per(6‐deoxy‐6‐thio‐2,3‐di‐O‐methyl)‐β‐cyclodextrin

A three‐step sequential self‐assembly procedure was applied in preparing gold electrodes modified in a stable and controlled way by a monolayer of thiolated β‐cyclodextrin (β‐CD), with methylene blue (MB) included in its cavity as the active component of the monolayer, and octanethiol as the nonelectroactive spacer blocking the electrode surface not occupied by β‐CD. MB acted as a mediator of electrons with respect to a solution soluble analyte, H₂O₂, and provided electrical contact between the electrode and solution resident enzyme, laccase, catalyzing reduction of oxygen to water.     

Voltammetric Determination of Metronidazole Using a Sensor Based on Electropolymerization of α‐Cyclodextrin over a Carbon Paste Electrode

An electrochemical sensor for metronidazole (MTZ) was built via the surface modification of a carbon paste electrode (CPE) by a film obtained through electropolymerization of α‐cyclodextrin (CPE_α‐CD). The CPE_α‐CD was characterized by cyclic voltammetry (CV) and atomic force microscopy (AFM), by both techniques was demonstrated that the polymer film is coating the electrode surface. The electroreduction behaviour of MTZ in HClO₄ media as a supporting electrolyte was studied by differential‐pulse voltammetric (DPV) technique. The DPV electrochemical process was observed to be diffusion controlled and irreversible. Under optimal conditions, the peak current was proportional to MTZ concentration in the range of 0.5 to 103.0 μM with a detection limit of 0.28±0.02 μM. The method was successfully applied to quantify of MTZ in pharmaceutical formulations. In addition, this proposed MTZ sensor exhibited good reproducibility, long‐term stability and fast current response.     

亚硫酸根在化学修饰电极上催化氧化的动力学表征

本文采用Saveant-Andrieux电催化反应动力学理论,表征了SO₃^2-在经Nation-Os(bpy)₃^2+/3+修饰后的玻碳电极上的电催化体系的动力学行为,用动力学区域图确定体系的动力学类型.当反应物浓度从8×10^-5变至1.28×10^-3(mol/L)时,体系始终遵循"SR"的动力学行为。     

同时测定多巴胺和肾上腺素的大环镍膜修饰电极

研究了大环镍膜修饰电极对多巴胺和肾上腺素的电化学响应特性；结果表明，该修饰电极对多巴胺和肾上腺素的电极反应具有良好的催化活性，多巴胺和肾上腺素在修饰电极上的氧化电位比在裸铂电极上分别负移了230mV和70mV，使二者的阳极峰得到很好的分离，且灵敏度大为提高；将该修饰电极用于多巴胺和肾上腺素的同时检测，获得满意结果，生物体中的主要干扰物质抗坏血酸和NO2^-等均不干扰测定。     

α-环糊精包结碳纳米管涂层电极同时测定多巴胺和肾上腺素

本文发现α-环糊精包结碳纳米管涂层电极对多巴胺（DA）和肾上腺素（EP）具有显著的增敏和电分离作用，还原峰电位差达390 mV。研究表明α-环糊精包结碳纳米管涂层薄膜表现出了非常令人感兴趣的电催化特性。因抗坏血酸（AA）在α-环糊精包结碳纳米管涂层电极上的氧化是不可逆的，因此利用还原峰进行测定，消除了AA对DA和EP的干扰。由于成本低和制作简便，该电极可用于生物系统电化学研究的生物传感器。     

石墨烯修饰玻碳电极对多巴胺的电催化氧化

通过3-巯丙基三乙氧基硅烷(METMS)将氧化石墨烯(GO)固载到玻碳电极(GCE)表面, 用电化学方法还原GO制备石墨烯修饰玻碳电极(rGO-METMS-GCE). 利用傅里叶变换红外光谱(FTIR)、 拉曼光谱(Raman)、 扫描电子显微镜(SEM)和原子力显微镜(AFM)等技术对GO和rGO-METMS-GCE的结构和表面形貌进行表征. 采用循环伏安(CV)和差分脉冲溶出伏安(DPV)法研究了rGO-METMS-GCE对多巴胺(DA)的电催化氧化性能及反应机理. 结果表明, 与裸GCE相比, DA在rGO-METMS-GCE电极上的氧化还原峰电流(i_pa和i_pc) 增大4倍, 氧化峰电位负移106 mV, 氧化峰与还原峰电位差(ΔE_p)从202 mV降低至66 mV, DA电化学氧化可逆性明显改善, 表明rGO-METMS-GCE对DA电化学氧化具有显著电催化作用. DA在rGO-METMS-GCE上的反应机理为单电子转移过程.     

Selective Electrochemical Determination of Uric Acid in the Presence of Ascorbic Acid Using a Carbon Paste Electrode Modified with β‐Cyclodextrin

Uric acid (UA) was determined in the presence of ascorbic acid (AA) by using a carbon paste electrode modified superficially by a β‐cyclodextrin film (CPE/β‐CD). The surface carbon paste electrode was prepared applying a 30 cycles potential program and using a 1 M HClO₄+0.01 M β‐CD electrolytic solution. The UA and AA solutions were used to evaluate the electrode selectivity and sensitivity by cyclic voltammetric and amperometric methods. In these experiments the detection limit for UA was (4.6±0.01)×10^?6 M and the RSD calculated from the amperometric curves was 10%. From the data obtained it was possible to quantify UA in the urine and saliva samples. Selective detection of UA was improved by formation of an inclusion complex between β‐CD and UA. The results show that the CPE/β‐CD is a good candidate due to its selectivity and sensitivity in the UA determination in complex samples like the biological fluids.     

Square‐Wave Voltammetric Detection of Dopamine at a Copper‐(3‐Mercaptopropyl) Trimethoxy Silane Complex Modified Electrode

Square‐wave voltammetric detection of dopamine was studied at a copper (Cu)‐(3‐mercaptopropyl) trimethoxy silane (MPS)‐complex modified electrode (Cu‐MPS). The modification of the electrode was based on the attachment of MPS onto an electrochemically activated glassy carbon electrode (GCE) by the interaction between methoxy silane groups of MPS and surface hydroxyl groups and followed by the complexation of copper with the thiol groups of MPS. The surface of the modified electrode was further coated by a thin layer of Nafion film. The surface of the Nafion coated MPS‐Cu complex modified electrode (Nafion/Cu‐MPS) was characterized using cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM), scanning electron microscope (SEM), X‐ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT‐IR) spectrometry. The modified electrode exhibited an excellent electrocatalytic activity towards the oxidation of dopamine, which was oxidized at a reduced potential of +0.35 V (vs. Ag/AgCl) at a wider pH range. Various experimental parameters, such as the amount of copper, the pH, and the temperature were optimized. A linear calibration plot was obtained in the concentration range between 8.0×10^?8 M and 5.0×10^?6 M and the detection limit was determined to be 5.0×10^?8 M. The other common biological compounds including ascorbic acid did not interfere and the modified electrode showed an excellent specificity to the detection of dopamine. The Nafion/Cu‐MPS modified electrode can be used for about 2 months without any significant loss in sensitivity.     

Gold Electrode Modified with Self‐Assembled Monolayer of Cysteamine‐Functionalized MWCNT and Its Application in Simultaneous Determination of Dopamine and Uric Acid

The voltammetric behavior of dopamine (DA) and uric acid (UA) on a gold electrode modified with self‐assembled monolayer (SAM) of cysteamine (CA) conjugated with functionalized multiwalled carbon nanotubes (MWCNTs) was investigated. The film modifier of functionalized SAM was characterized by means of scanning electron microscopy (SEM) and also, electrochemical impedance spectroscopy (EIS) using para‐hydroquinone (PHQ) as a redox probe. For the binary mixture of DA and UA, the voltammetric signals of these two compounds can be well separated from each other, allowing simultaneous determination of DA and UA. The effect of various experimental parameters on the voltammetric responses of DA and UA was investigated. The detection limit in differential pulse voltammetric determinations was obtained as 0.02 µM and 0.1 µM for DA and UA, respectively. The prepared modified electrode indicated a stable behavior and the presence of surface COOH groups of the functionalized MWCNT avoided the passivation of the electrode surface during the electrode processes. The proposed method was successfully applied for the determination of DA and UA in urine samples with satisfactory results. The response of the gold electrode modified with MWCNT‐functionalized SAM method toward DA, UA, and ascorbic acid (AA) oxidation was compared with the response of the modified electrode prepared by the direct casting of MWCNT.     

Electrochemical Oxidation of Methionine Mediated by a Fullerene‐C60 Modified Gold Electrode

The usefulness of a C₆₀‐fullerene modified gold (Au) electrode in mediating the oxidation of methionine in the presence of potassium ions electrolyte has been demonstrated. During cyclic voltammetry, an oxidation peak of methionine appearing at +1.0 V vs. Ag/AgCl was observed. The oxidation current of methionine is enhanced by about 2 times using a C₆₀ modified gold electrode. The current enhancement is significantly dependent on pH, temperature and C₆₀ dosage. Calibration plot reveals linearity of up to 0.1 mM with a current sensitivity of close to 50 mA L mol^?1 and detection limit of 8.2×10^?6 M. The variation of scan rate study shows that the system undergoes diffusion‐controlled process. Diffusion coefficient and rate constant of methionine were determined using hydrodynamic method (rotating disk electrode) with values of 1.11×10^?5 cm² s^?1 and 0.0026 cm s^?1 respectively for unmodified electrode while the values of diffusion coefficient and rate constant of methionine using C₆₀ modified Au electrode are 5.7×10^?6 cm² s^?1 and 0.0021 cm s^?1 respectively.