Electrocatalysis of Puerarin on a Nano-CeO2/MWCNTs Composite Modified Electrode and Its Determination in Pharmaceutical Preparations

A good route for the fabrication of CeO₂ nanoparticles (nano‐CeO₂)/multi‐walled carbon nanotubes (MWCNTs) modified glassy carbon electrodes (GCE) was proposed. MWCNTs are used to immobilize nano‐CeO₂. What′s more, with the addition of the MWCNTs, the agglomeration level of CeO₂ nanoparticles can be reduced, the extremely large surface area can be obtained and the electron transfer rate can be increased. The morphological characterization of nano‐CeO₂/MWCNTs was examined by scanning electron microscopy (SEM). The performances of the nano‐CeO₂/MWCNTs/GCE were characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and typical amperometric response (i‐t). The potential utility of the constructed electrodes was demonstrated by applying them to the analytical determination of puerarin concentration. The catalytic oxidation of puerarin has a better result on nano‐CeO₂/MWCNTs/GCE because of the synergistic effect of nano‐CeO₂ and MWCNTs. An optimized limit of detection of 8.0×10^?9 mol/L was obtained at a signal‐to‐noise ratio of 3 and with a fast response time (within 3 s). Additionally, the nano‐CeO₂/MWCNTs/GCE exhibited a wide linear range from 0.04 to 6.0 μmol/L and high sensitivity.     

Hydrogen Peroxide Sensor Based on Carbon Nanotubes/β‐Ni(OH)2 Nanocomposites

Ni(OH)₂ nanoflowers were synthesized by a simple and energy‐efficient wet chemistry method. The product was characterized by scanning electron microscopy (SEM) and X‐ray powder diffraction (XRD). Then Ni(OH)₂ nanoflowers attached multi‐walled carbon nanotubes (MWCNTs) modified glassy carbon electrodes (GCE) were proposed (MWCNTs/Ni(OH)₂/GCE) to use as electrochemical sensor to detect hydrogen peroxide. The results showed that the synergistic effect was obtained on the MWCNTs/Ni(OH)₂/GCE whose sensitivity was better than that of Ni(OH)₂/GCE. The linear range is from 0.2 to 22 mmol/L, the detection limit is 0.066 mmol/L, and the response time is <5 s. Satisfyingly, the MWCNTs/Ni(OH)₂/GCE was not only successfully employed to eliminate the interferences from uric acid (UA), acid ascorbic (AA), dopamine (DA), glucose (GO) but also NO₂^? during the detection. The MWCNTs/Ni(OH)₂/GCE allows highly sensitive, excellently selective and fast amperometric sensing of hydrogen peroxide and thus is promising for the future development of hydrogen peroxide sensors.     

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.     

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%。     

Electroanalysis of Bisphenol A at a Multiwalled Carbon Nanotubes‐gold Nanoparticles Modified Glassy Carbon Electrode

A sensitive electrochemical method was developed for the determination of bisphenol A (BPA) at a glassy carbon electrode (GCE) modified with a multiwalled carbon nanotubes (MWCNTs)‐gold nanoparticles (GNPs) hybrid film, which was prepared based on the electrostatic interaction between positively charged cetyltrimethylammonium bromide (CTAB) and negatively charged MWCNTs and GNPs. The MWCNT‐GNPs/GCE exhibited an enhanced electroactivity for BPA oxidation versus unmodified GCE and MWCNTs/GCE. The experimental parameters, including the amounts of modified MWCNTs and GNPs, the pH of the supporting electrolyte, scan rate and accumulation time, were examined and optimized. Under the optimal conditions, the differential pulse voltammetric anodic peak current of BPA was linear with the BPA concentration from 2.0×10^?8 to 2×10^?5 mol L^?1, with a limit of detection of 7.5 nmol L^?1. The proposed procedure was applied to determine BPA leached from real plastic samples with satisfactory results.     

Ultrasensitive Voltammetric Detection of Trace Lead(II) and Cadmium(II) Using MWCNTs‐Nafion/Bismuth Composite Electrodes

Multiwall carbon nanotubes were dispersed in Nafion (MWCNTs‐NA) solution and used in combination with bismuth (MWCNTs‐NA/Bi) for fabricating composite sensors to determine trace Pb(II) and Cd(II) by differential pulse anodic stripping voltammetry (DPASV). The electrochemical properties of the MWCNTs‐NA/Bi composites film modified glassy carbon electrode (GCE) were evaluated. The synergistic effect of MWCNTs and bismuth composite film was obtained for Pb(II) and Cd(II) detection with improved sensitivity and reproducibility. Linear calibration curves ranged from 0.05 to 100 μg/L for Pb(II) and 0.08 to 100 μg/L for Cd(II). The determination limits (S/N=3) were 25 ng/L for Pb and 40 ng/L for Cd, which compared favorably with previously reported methods in the area of electrochemical Pb(II) and Cd(II) detection. The MWCNTs‐NA/Bi composite film electrodes were successfully applied to determine Pb(II) and Cd(II) in real sample, and the results of the present method agreed well with those of atomic absorption spectroscopy.     

Electrochemical Study and Application on Shikonin at Poly(diallyldimethylammonium chloride) Functionalized Graphene Sheets Modified Glass Carbon Electrode

The electrochemical behaviors of shikonin at a poly(diallyldimethylammonium chloride) functionalized graphene sheets modified glass carbon electrode(PDDA-GS/GCE) have been investigated. Shikonin could exhibit a pair of well-defined redox peaks at the PDDA-GS/GCE located at 0.681 V(E_pa) and 0.662 V(E_pc)[vs. saturated calomel electrode(SCE)] in 0.1 mol/L phosphate buffer solution(pH=2.0) with a peak-to-peak separation of about 20 mV, revealing a fast electron-transfer process. Moreover, the current response was remarkably increased at PDDA-GS/GCE compared with that at the bare GCE. The electrochemical behaviors of shikonin at the modified electrode were investigated. And the results indicate that the reaction involves the transfer of two electrons, accompanied by two protons and the electrochemical process is a diffusional-controlled electrode process. The electrochemical parameters of shikonin at the modified electrode, the electron-transfer coefficient(α), the electron-transfer number(n) and the electrode reaction rate constant(k_s) were calculated to be as 0.53, 2.18 and 3.6 s^-1, respectively. Under the optimal conditions, the peak current of differential pulse voltammetry(DPV) increased linearly with the shikonin concentration in a range from 9.472×10^-8 mol/L to 3.789×10^-6 mol/L with a detection limit of 3.157×10^-8 mol/L. The linear regression equation was I_p=0.7366c+0.7855(R=0.9978; I_p: 10^-7 A, c: 10^-8 mol/L). In addition, the modified glass carbon electrode also exhibited good stability, selectivity and acceptable reproducibility that could be used for the sensitive, simple and rapid determination of shikonin in real samples. Therefore, the present work offers a new way to broaden the analytical application of graphene in pharmaceutical analysis.     

电聚合β-环糊精修饰电极的制备及其对铜离子的检测

采用循环伏安法(CV),由β-环糊精(β-CD)单体在玻碳电极(GCE)表面电聚合制得聚β-CD膜修饰电极(β-CD/GCE)。实验表明,β-CD/GCE对Cu2+具有明显的电催化作用,在pH=5.85的磷酸盐缓冲溶液(PBS)中,Cu2+浓度与其峰电流在4.01×10-4～1.05×10-7 mol·L-1范围内呈良好的线性关系,线性方程为:ip=-1.975c-1.336×10-4(i:A,c:mol·L-1),相关系数R=0.9981,检出限(S/N=3)为5.03×10-8mol·L-1。方法应用于实际样品测定,回收率在98.0%～103%之间。     

复合修饰电极测定p-硝基苯酚新方法的研究与探讨

将多壁碳纳米管分散在孔雀绿溶液中并滴涂在玻碳电极表面,再电聚合一层孔雀绿膜,制备了一种新型的聚孔雀绿/多壁碳纳米管复合膜修饰玻碳电极.用电化学方法对所制得的复合修饰电极进行了表征,并研究了p-硝基苯酚在该电极上的电化学行为.结果表明,所制备的复合修饰电极对P-硝基苯酚有良好的电催化作用,从而建立了一种直接测定P-硝基苯...     

Avidin and Glucose Oxidase‐non‐covalently Functionalized Multi‐walled Carbon Nanotubes: A New Analytical Tool for Building a Bienzymatic Glucose Biosensor

We report an innovative supramolecular architecture for bienzymatic glucose biosensing based on the non‐covalently functionalization of multi‐walled carbon nanotubes (MWCNTs) with two proteins, glucose oxidase (GOx) (to recognize glucose) and avidin (to allow the specific anchoring of biotinylated horseradish peroxidase (b‐HRP)). The optimum functionalization was obtained by sonicating for 10 min 0.50 mg mL^?1 MWCNTs in a solution of 2.00 mg mL^?1 GOx+1.00 mg mL^?1avidin prepared in 50 : 50 v/v ethanol/water. The sensitivity to glucose for glassy carbon electrodes (GCE) modified with MWCNTs‐GOx‐avidin dispersion and b‐HRP (GCE/MWCNTs‐GOx‐avidin/b‐HRP), obtained from amperometric experiments performed at ?0.100 V in the presence of 5.0×10^?4 M hydroquinone, was (4.8±0.3) μA mM^?1 (r²=0.9986) and the detection limit was 1.2 μM. The reproducibility for 5 electrodes using the same MWCNTs/GOx‐avidin dispersion was 4.0 %, while the reproducibility for 3 different dispersions and 9 electrodes was 6.0 %. The GCE/MWCNT‐GOx‐avidin/b‐HRP was successfully used for the quantification of glucose in a pharmaceutical product and milk.     

Electrochemical behavior and voltammetric determination of norfloxacin at glassy carbon electrode modified with multi walled carbon nanotubes/Nafion

A simple and rapid electrochemical method is developed for the determination of trace-level norfloxacin, based on the excellent properties of multi-walled carbon nanotubes (MWCNTs). The MWCNTs/Nafion film-coated glassy carbon electrode (GCE) is constructed and the electrochemical behavior of norfloxacin at the electrode is investigated in detail. The results indicate that MWCNTs modified glassy carbon electrode exhibited efficiently electrocatalytic oxidation for norfloxacin (NFX) with relatively high sensitivity, stability and life time. Under conditions of cyclic voltammetry, the current for oxidation of selected analyte is enhanced significantly in comparison to the bare GCE. The electrocatalytic behavior is further exploited as a sensitive detection scheme for the analyte determinations by linear sweep voltammetry (LSV). Under optimized condition in voltammetric method the concentration calibration range and detection limit (S/N=3) are 0.1-100 micromol/L and 5 x 10(-8)mol/L for NFX. The proposed method was successfully applied to NFX determination in tablets. The analytical performance of this sensor has been evaluated for detection of the analyte in urine as a real sample.     

Sensitive Nucleic Acid Detection at NH2‐MWCNTs Modified Glassy Carbon Electrode and its Application for Monitoring of Gemcitabine‐DNA Interaction

An electrochemical dsDNA nanobiosensor was fabricated using amino‐functionalized multi walled carbon nanotubes modified glassy carbon electrode (NH₂fMWCNTs/GCE) for the sensitive detection of DNA bases and electrochemical monitoring of drug‐DNA interaction. The influence of functional groups on MWCNT was studied by MWCNT functionalized with NH₂ (NH₂fMWCNTs) and COOH (COOHfMWCNT) groups based on the signal of DNA bases. The modified electrodes were characterized by scanning electron microscopy. One layer of calf thymus double stranded deoxyribonucleic acid (ct‐dsDNA) was immobilized onto the NH₂fMWCNTs/GCE (dsDNA/NH₂fMWCNTs/GCE). The dsDNA/NH₂fMWCNTs/GCE were used to investigate the interaction between the dsDNA and the anticancer drug gemcitabine by differential pulse voltammetry in acetate buffer of pH 4.70. For the confirmation of interaction, the lowering in intensity of the current signals of guanine and adenine was considered as an indicator. Electrochemical impedance spectroscopy studies were performed for the comparison of the modified surfaces. In order to define and visualize the interaction mechanism between gemcitabine and dsDNA/NH₂fMWCNTs/GCE at the molecular level, in silico methods including docking and molecular dynamics simulations were employed.     

A promising electrochemical sensing platform based on copper nanoparticles-decorated polymer in carbon nanotube electrode for monitoring methimazole

In this paper, a novel and convenient electrochemical sensor for detection of methimazole (MMI) by differential pulse voltammetry is presented. This sensor was fabricated by dripping well-dispersed MWCNTs onto glassy carbon electrode (GCE) surface, and then poly-l-Arg (P-L-Arg) film was deposited on the electrode. Finally, Cu nanoparticles (CuNPs) were electrochemically deposited on the resulting film by using cyclic voltammetry to prepare CuNPs-P-L-Arg/MWCNTs/GCE. The surface morphology of the electrodes has been studied by scanning electron microscopy. Studies reveal that the irreversible oxidation of MMI was highly facile on CuNPs-P-L-Arg/MWCNTs/GCE. The dynamic detection range of this sensor to MMI was 5.2–50 µM, with the detection limit of 2 µM. A new voltammetric method for determination of MMI was erected and shows good sensitivity and selectivity, very easy surface update and good stability. The analytical application of the modified electrode is demonstrated by determining MMI in biological fluids (serum).     

Very sensitive differential pulse adsorptive stripping voltammetric determination of 4-nitrophenol at poly (diphenylamine)/multi-walled carbon nanotube-β-cyclodextrin-modified glassy carbon electrode

In this work, a glassy carbon electrode (GCE) modified with poly (diphenylamine)/multi-walled carbon nanotubes-β-cyclodextrin (PDPA/MWCNT-β-CD) film was constructed and used for the determination of 4-nitrophenol (4-NP). Diphenylamine was successfully electropolymerised onto MWCNT-β-CD-modified GCE by cyclic voltammetry in monomer solution and 5 mol L^?1 H₂SO₄. The surface morphology of PDPA/MWCNT-β-CD film was characterised using scanning electron microscopy and electrochemical impedance spectroscopy. After adsorption of 4-NP on PDPA/MWCNT-β-CD at 0.2 V for 150 s, it showed a well-defined reduction peak in phosphate buffer solution at pH = 7. The PDPA/MWCNT-β-CD film enhanced the reduction peak current due to the complex formation between β-CD and 4-NP, presence of conductive polymer film as electron transfer mediator and also ability of MWCNTs for strong adsorptive and catalytic effect. Peak current increased linearly with 4-NP concentration in the range of 0.1 to 13.9 µg L^?1. The detection limit was obtained as 0.02 µg L^?1, which is better than other reported detection limits for the determination of 4-NP. The results showed that modified electrode has good sensitivity and selectivity. This sensor was used for the determination of 4-NP in water samples.     

Electrochemical Determination of Phenylethanolamine A Based on Nafion/MWCNTs/AuNPs Modified Carbon Electrode

Phenylethanolamine A (PEA), a β‐agonist, was found to be illegally used as a growth promoter in pigs last year, causing Chinese government's great attention. Here, a sensitive electrochemical method was developed for detecting PEA by immobilization of gold nanoparticles (AuNPs), multiwalled carbon nanotubes (MWCNTs) and Nafion on the surface of a glassy carbon electrode (GCE). The Nafion/MWCNTs/AuNPs film was characterized by scanning electronic micrographs (SEM) and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of PEA at the modified GCE were investigated in detail. The synergetic effects of AuNPs, MWCNTs and Nafion amplify the electrochemical reduction signal of PEA, and result in high sensitivity for PEA determination. Under the optimal conditions, the electrochemical sensor shows a wide linear range of 0.01 to 10 (mol/L with a detection limit of 0.005 µmol/L. Moreover, the fabricated sensor presents high selectivity and long‐term stability, which paves a new way for simple, rapid, sensitive detection of PEA.     

壳聚糖/多壁碳纳米管复合膜电化学手性识别色氨酸对映异构体

采用滴涂方式将羧酸化多壁碳纳米管(f-MWCNTs)修饰于玻碳电极(GCE)表面成膜,然后恒电位法在上述修饰电极表面电沉积壳聚糖(CS)膜,形成CS和f-MWCNTs复合膜修饰电极(CS/f-MWCNTs/GCE),并用于色氨酸(Trp)对映异构体的手性识别。采用扫描电子显微镜(SEM)表征了修饰电极表面形貌的差异,电化学阻抗(EIS)和循环伏安法(CV)研究修饰电极的电化学行为差异。差分脉冲伏安法(DPV)用于区别色氨酸(Trp)对映异构体,分离系数可达2.38。研究发现该修饰电极对L-Trp的DPV响应信号强于D-Trp,检测的线性范围为8.0×10~(-6)~4.0×10~(-3)mol/L,检出限(S/N=3)为5.0×10~(-6)mol/L。该方法简单、经济、快速,对发展其它手性化合物的检测方法提供了参考。     

Electrochemical behavior of brilliant cresyl violet at multi-wall carbon nanotubes/Nafion modified glassy carbon electrode and its interaction with cyclodextrins

Multi-wall carbon nanotubes (CNTs)/Nafion composite membrane modified glassy carbon electrode (GCE) was fabricated to investigate the redox of brilliant cresyl violet (BCV) and its supramolecular system with γ-CD and hydroxypropyl-γ-CD (HP-γ-CD). The cyclic voltammetric results indicated that MWNTs/Nafion composite membrane was able to electrocatalyze the redox of BCV compared with bare GCE. Under optimal conditions, differential pulse voltammetry (DPV) was used to study the inclusion interaction of BCV with γ-CD and HP-γ-CD. The consequence demonstrated that the formation of complexes led to the rise of peak current and the shift of peak potential. The inclusion constants of BCV dimer with γ-CD, HP-γ-CD are 2,650 and 8,040 L/mol, respectively. UV–Vis spectra were also employed to confirm the formation of complexes. According to ¹HNMR, the possible binding mode of BCV dimer with CDs was discussed.     

聚(3-氨基-5-巯基-1,2,4-三唑)/多壁碳纳米管修饰的玻碳电极同时检测尿酸、黄嘌呤与次黄嘌呤

采用滴涂法得到多壁碳纳米管(MWCNTs)修饰的玻碳电极(GCE),通过电沉积方法将3-氨基-5-巯基-1,2,4-三唑(TA)沉积在MWCNTs/GCE表面,制备了聚(3-氨基-5-巯基-1,2,4-三唑)/多壁碳纳米管修饰电极(p TA/MWCNTs/GCE)。采用循环伏安法(CV)和示差脉冲伏安法(DPV),研究了尿酸(UA)、黄嘌呤(XA)和次黄嘌呤(HX)在该修饰电极上的电化学行为。结果表明,该修饰电极对UA、XA和HX均有较好的电催化活性作用,能实现对3种物质的同时测定。UA、XA和HX在该修饰电极上的线性范围分别为9.0~739.0、2.0~259.0、1.0~353.0μmol/L;检出限分别为0.67、0.17、0.33μmol/L。该修饰电极已成功用于尿液和血清实际样品中UA、XA和HX的同时测定,回收率为98.8%~105.5%。     

Sensitive determination of hydrazine using poly(phenolphthalein), Au nanoparticles and multiwalled carbon nanotubes modified glassy carbon electrode

This study reports a detailed analysis of an electrode material containing poly(phenolphthalein), carbon nanotubes and gold nanoparticles which shows superior catalytic effect towards to hydrazine oxidation in Britton–Robinson buffer (pH 10.0). Glassy carbon electrode was modified by electropolymerization of phenolphthalein (PP) monomer (poly(PP)/GCE) and the multiwalled carbon nanotubes (MWCNTs) was dropped on the surface. This modified surface was electrodeposited with gold nanoparticles (AuNPs/CNT/poly(PP)/GCE). The fabricated electrode was analysed the determination of hydrazine using cyclic voltammetry, linear sweep voltammetry and amperometry. The peak potential of hydrazine oxidation on bare GCE, poly(PP)/GCE, CNT/GCE, CNT/poly(PP)/GCE, and AuNPs/CNT/poly(PP)/GCE were observed at 596 mV, 342 mV, 320 mV, 313 mV, and 27 mV, respectively. A shift in the overpotential to more negative direction and an enhancement in the peak current indicated that the AuNPs/CNT/poly(PP)/GC electrode presented an efficient electrocatalytic activity toward oxidation of hydrazine. Modified electrodes were characterized with High-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Amperometric current responses in the low hydrazine concentration range of 0.25–13 µM at the AuNPs/CNT/poly(PP)/GCE. The limit of detection (LOD) value was obtained to be 0.083 µM. A modified electrode was applied to naturel samples for hydrazine determination.     

电还原氧化石墨烯-金纳米棒修饰电极对酒石黄的测定

本文制备了氧化石墨烯-金纳米棒复合物(GO-GNRs).利用滴涂法制备了修饰电极(GO-GNRs/GCE),通过循环伏安法,还原了GO-GNRs复合物中的GO,制得电化学还原的石墨烯-金纳米棒修饰电极(ERGO-GNRs/GCE).研究了酒石黄在不同电极上的电流响应,结果表明,ERGO-GNRs/GCE对酒石黄的氧化有很好的电催化作用,其浓度在0.05～6.0μmol/L范围内与氧化峰电流呈良好的线性关系,检出限为15 nmol/L.利用ERGO-GNRs/GCE可完成样品中酒石黄含量的测定.