Functionalization of multi-walled carbon nanotubes with poly(amidoamine) dendrimer for mediator-free glucose biosensor

By grafting with poly(amidoamine) (PAMAM) dendrimer, novel carbon nanotube (CNT) nano-composites have been successfully prepared. The novel functionalized matrix with plenty amino groups circumvents the troublesome solubility problem of CNTs in solvents, especially in water, greatly expanding the scope of the application of carbon nanotubes. The GO_x and HRP immobilized CNT-PAMAM based on the functional CNTs was synthesized. The bi-enzymatic CNT-PAMAM nano-composites are highly dispersible in water and show very promising applications in the fabrication of mediator-free bi-enzymatic biosensors for sensitive detection of glucose. The cooperation of nano-composite between CNT and high dense GO_x and HRP results in very high sensitivity to glucose with a current response of 2200 nA mM⁻¹ and fast response (∼1 s). The modified electrode exhibits a wide linear response range for glucose from 4.0 μM to 1.2 mM (R = 0.9971, N = 15), with a detection limit of 2.5 μM. The negative electrode potential of −0.34 V is favorable for glucose detection in real samples without interference caused by other biomolecules.     

Glassy carbon electrodes modified by multiwalled carbon nanotubes and poly(neutral red): A comparative study of different brands and application to electrocatalytic ascorbate determination

The electrochemical behaviour of glassy carbon electrodes coated with multiwalled carbon nanotubes (MWCNT) from three different sources and with different loadings has been compared, with a view to sensor applications. Additionally, poly(neutral red) (PNR) was electrosynthesised by potential cycling on bare glassy carbon and on MWCNT-modified glassy carbon electrodes, and characterised by cyclic voltammetry and scanning electron microscopy. Well-defined voltammetric responses were observed for hexacyanoferrate (II) oxidation with differences between the MWCNT types as well as from loading. The MWCNT and PNR/MWCNT-modified electrodes were applied to the oxidative determination of ascorbate, the electrocatalytic effects observed varying according to the type of nanotubes. Comparison was made with electrodes surface-modified by graphite powder. All modified electrode configurations with and without PNR were successfully employed for ascorbate oxidation at +0.05 V vs saturated calomel electrode with detection limits down to 4 μM; good operational stability and storage stability were also obtained.     

基于多壁碳纳米管/壳聚糖多层膜修饰玻碳电极邻苯二酚的测定

改进了碳纳米管在壳聚糖溶液中的分散方法,制备了多壁碳纳米管/壳聚糖多层膜修饰玻碳电极,对比了不同修饰层数膜电极的循环伏安和电化学阻抗行为,5层多壁碳纳米管/壳聚糖膜修饰玻碳电极的电化学性能优良.在最优实验条件下,该修饰玻碳电极对邻苯二酚(CAT)有灵敏的响应,CAT浓度在3.99×10-6～9.09×10-4mol/L范围内与氧化峰电流呈良好的线性关系,检出限为2.39×10-6mol/L(S/N=3).该修饰玻碳电极性能稳定,测定4×10-5mol/LCAT溶液,RSD(n=10)为2.1%;15周后,该电极的响应值仅降低1.9%.     

Spectroelectrochemical and electrochromic behavior of poly(methylene blue) and poly(thionine)-modified multi-walled carbon nanotubes

Journal of Solid State Electrochemistry - The increasing efforts devoted to fabricating electrochromic (EC) devices have motivated a lot of studies to develop new EC materials. Herein, we introduce...     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Poly(lactic acid) composites with poly(lactic acid)‐modified carbon nanotubes

This work reports the study of the effect of chemical functionalization of carbon nanotubes on their dispersion in poly(lactic acid). The nanotubes were functionalized by the 1,3‐dipolar cycloaddition reaction, generating pyrrolidine groups at the nanotube surface. Further reaction of the pyrrolidine groups with poly(lactic acid) was studied in solution and in the polymer melt. The former involved refluxing the nanotubes in a dimethylformamide/polymer solution; the latter was carried out by direct melt mixing in a microcompounder. The carbon nanotubes collected after each process were characterized by thermogravimetry and by X‐ray photoelectron spectroscopy, showing evidence of polymer bonded to the nanotube surface only when the reaction was carried out in the polymer melt. The composites with polymer modified nanotubes present smaller average agglomerate area and a narrower agglomerate area distribution. In addition, they show improved tensile properties at low CNT concentration and present lower electrical resistivity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3740–3750     

Carbon electrode modified with ionic liquid and multi-walled carbon nanotubes for voltammetric sensing of adenine

A voltammetric sensor was fabricated by applying a Nafion and multi-walled carbon nanotubes (MWCNTs) composite film on the surface of a carbon ionic liquid electrode (CILE), which was prepared by mixing 1-butyl-3-methylimidazolium hexafluorophosphate with graphite powder. The electrochemical behavior of adenine on the Nafion-MWCNTs/CILE was investigated in pH 5.5 buffer solution. Adenine showed an irreversible adsorption-controlled oxidation reaction with enhanced electrochemical response, which was due to the presence of high conductive MWCNTs on the CILE surface. The electrochemical parameters of adenine electro-oxidation were determined, and the experimental conditions were optimized. Under the optimal conditions, the oxidation peak current was linear to the adenine concentration over the range of 1.0?×?10^?7 to 7.0?×?10^?5 mol L^?1 with a detection limit of 3.3?×?10^?8 mol L^?1 (signal/noise?=?3). The electrode showed good stability and selectivity, and was further applied to milk powder samples with satisfactory results.     

氢氧化镍/多壁碳纳米管复合材料的溶剂热法制备及电容性能

采用溶剂热法制备了氢氧化镍/多壁碳纳米管[Ni(OH)2/MWCNTs]复合纳米材料;借助X射线衍射仪和透射电镜分析了产物的结构和形貌,利用循环伏安测试测定了复合材料的电容特性.结果表明:片状β-Ni(OH)2较好地附着在MWCNTs上;复合样品的循环伏安行为明显有别于空白样品Ni(OH)2,峰电流较高.这表明引入MWCNTs可改善Ni(OH)2的电化学性能.与此同时,当MWCNTs的质量分数为10%时,相应的Ni(OH)2/MWCNTs复合物的氧化还原峰电位差最小,循环可逆性最佳.     

Voltammetric evaluation of the antioxidant capacity of tea on electrodes modified with multi-walled carbon nanotubes

The characteristics of the voltammograms of tea polyphenols on a glassy carbon electrode modified with multi-walled carbon nanotubes (MCNT-GCE) were evaluated. With the use of atomic force microscopy, it was found that MCNTs are oriented as rows 0.8–1.0 μm wide with alternating hills to 586 nm in height. Polyphenols other than of tannin are reversibly oxidized at the first step. Corresponding electrode reaction schemes are proposed. A voltammetric procedure for the estimation of the antioxidant capacity (AOC) of tea based on the oxidation of its polyphenol compounds was developed. The voltammograms of tea exhibited clearly defined peaks and oxidation steps whose potentials depend on the type of tea. The area of oxidation peaks was chosen as the parameter that characterizes antioxidant properties. The AOC of tea was expressed in terms of catechin equivalents per 100 mL of a beverage. 27 tea samples were analyzed. It was found that the AOC of green tea is 79% higher than that of black tea (290 ± 40 and 54 ± 22 mg/100 mL, respectively, P < 0.05). The AOC of oolong tea (70 ± 5 mg/100 mL) is considerably lower than that of green tea and statistically insignificantly higher than that of black tea. The AOC of white tea is comparable with the AOC of green tea (255 ± 11 and 290 ± 40 mg/100 mL, respectively, P > 0.05).     

Characterization of electrodes modified with nanocomposites of cobalt tetraaminophenoxyphthalocyanine,reduced graphene and multi-walled carbon nanotubes

Abstract

Glassy carbon electrodes or plates were modified with nanocomposites consisting of cobalt tetraaminophenoxyphthalocyanine (CoTAPhPc), reduced graphene oxide nanosheets (rGONs) and multi-walled carbon nanotubes (MWCNTs). The modified electrodes were characterized using cyclic voltammetry, scanning electrochemical microscopy (SECM) and time-of-flight-secondary ion mass spectrometer (TOF-SIMS). The electrocatalytic activity of the modified electrode was tested for detection of L-cysteine. The presence of CoTAPhPc on sequential layers of MWCNT and rGONs resulted in improved detection currents compared to CoTAPhPc alone or when MWCNT/rGONs are mixed in CoTAPhPc–MWCNT/rGONs (mix)–glassy carbon electrode (GCE). CoTAPhPc–MWCNT–GCE (without rGONS) showed higher sensitivity toward l-cysteine as compared to the probes incorporating rGONs with a catalytic rate constant of 4.62?×?10⁴ M^?1s^?1 and a detection limit of 30?nM. The presence of rGONs improved the stability of the electrode.     

One-step functionalization of multi-walled carbon nanotubes by radiation-induced graft polymerization and their application as enzyme-free biosensors

This paper describes the functionalization of multi-walled carbon nanotubes (MWNTs) by radiation-induced graft polymerization (RIGP) of vinyl monomers with functional groups and the application of these MWNTs in enzyme-free biosensors. The vinyl monomers used were acrylic acid (AAc), methacrylic acid (MAc), glycidyl methacrylate (GMA), maleic anhydride (MAn), and 4-vinylphenylboronic acid (VPBAc). Tubular-type MWNTs were obtained via RIGP of various vinyl monomers. The poly(VPBAc)-grafted MWNTs (PVBAc-g-MWNTs) were used as sensing sites in enzyme-free glucose sensors for the detection of glucose without enzymes. The PVBAc-g-MWNTs electrode displayed an excellent linear response to glucose concentration in the range 1.0–10 mM. The functionalized MWNTs prepared by RIGP can be used as biosensor materials.     

Characterisation of poly(neutral red) modified carbon film electrodes; application as a redox mediator for biosensors

The polymer redox mediator, poly(neutral red) (PNR), has been synthesised and characterised electrochemically to investigate the best electropolymerisation and mediation conditions for application in enzyme biosensors and to clarify the mechanism of action. Neutral red was electropolymerised by potential cycling on carbon film electrode substrates by allowing the monomer to be oxidised during the full 20 cycles of polymerisation or reducing the positive limit of the potential window after the first 2 cycles to impede monomer oxidation with a view to obtaining longer polymer chains and a lesser degree of branching. Comparison was made with glassy carbon substrates. The PNR films on carbon film electrodes were characterised using cyclic voltammetry and electrochemical impedance spectroscopy, as well as in glucose biosensors prepared with PNR. Glucose oxidase enzyme was immobilised by encapsulation in silica sol-gel and compared with that obtained by cross-linking with glutaraldehyde. The biosensors were evaluated by chronoamperometry in 0.1 M phosphate buffer saline solution, pH 7.0, and showed evidence of electron transfer between the enzyme cofactor flavin adenine dinucleotide and PNR dissolved in the enzyme layer competing with PNR-mediated electrochemical degradation of H₂O₂ formed during the enzymatic process. This paper is dedicated to Professor Dr. Algirdas Vaskelis on the occasion of his 70th birthday.     

Electrochemical behavior and determination of fluphenazine at multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane bilayer modified gold electrodes

A novel multi-walled carbon nanotubes/(3-mercaptopropyl)trimethoxysilane (MPS) bilayer modified gold electrode was prepared and used to study the electrochemcial behavior of fluphenazine and determine it. Fluphenazine could effectively accumulate at this electrode and produce two anodic peaks at about 0.78 V and 0.93 V (versus SCE). The peak at about 0.78 V was much higher and sensitive, thus it could be applied to the determination. Various conditions were optimized for practical application. Under the selected conditions (i.e. 0.05 M pH 3.5 HCOOH-HCOONa buffer solution, 5 μl 1 mg ml⁻¹ multi-walled carbon nanotubes for Φ=2.0 mm electrode, accumulation at open circuit for 180 s), the anodic peak current was linear to fluphenazine concentration in the range from 5×10⁻⁸ to 1.5×10⁻⁵ M with correlation coefficient of 0.9984, the detection limit was 1×10⁻⁸ M. For a 1×10⁻⁵ M fluphenazine solution, the relative standard deviation of peak current was 2.51% (n=8). This method was successfully applied to the determination of fluphenazine in drug samples and the recovery was 96.4-104.4%. The electrode could be easily regenerated and exhibited some selectivity, but some surfactants reduced the peak current greatly. The modified electrode was characterized by alternating current impedance and electrochemical probe.     

Fabrication of prussian blue/multi-walled carbon nanotubes modified electrode for electrochemical sensing of hydroxylamine

We are presenting a sensor for hydroxylamine that is based on an glassy carbon electrode modified with nanoparticles of Prussian Blue and with multi-walled carbon nanotubes (MWCNTs). The sensing material was synthesized using a mixture of ferric chloride and potassium ferricyanide solution in the presence of MWCNTs under ambient conditions. Characterization was done by scanning electron microscopy, UV-vis spectroscopy, Fourier transform infrared absorption spectrum and cyclic voltammetry. The modified electrode showed two well-defined pairs of redox peaks and dramatic catalytic activity towards the electro-oxidation of hydroxylamine with a linear response ranging from 1.5 µM to 2.0 mM. In addition, tests show the sensor exhibited outstanding stability and reproducibility.     

Polyaniline and poly(flavin adenine dinucleotide) doped multi-walled carbon nanotubes for p-acetamidophenol sensor

A conductive biocomposite film (MWCNTs-PANIFAD) which contains multi-walled carbon nanotubes (MWCNTs) along with the incorporation of poly(aniline) and poly(flavin adenine dinucleotide) co-polymer (PANIFAD) has been synthesized on gold and screen printed carbon electrodes by potentiostatic methods. The presence of MWCNTs in the MWCNTs-PANIFAD biocomposite film enhances the surface coverage concentration (Γ) of PANIFAD and increases the electron transfer rate constant (k_s) to 89%. Electrochemical quartz crystal microbalance studies reveal the enhancements in the functional properties of MWCNTs and PANIFAD present in MWCNTs-PANIFAD biocomposite film. Surface morphology of the biocomposite film has been studied using scanning electron microscopy and atomic force microscopy. The surface morphology results reveal that PANIFAD incorporated on MWCNTs. The MWCNTs-PANIFAD biocomposite film exhibits promising enhanced electrocatalytic activity towards the oxidation of p-acetamidophenol. The cyclic voltammetry has been used for the measurement of electroanalytical properties of p-acetamidophenol by means of PANIFAD, MWCNTs and MWCNTs-PANIFAD biocomposite film modified gold electrodes. The sensitivity value of MWCNTs-PANIFAD film (88.5 mA mM⁻¹ cm⁻²) is higher than the values which are obtained for PANIFAD (28.7 mA mM⁻¹ cm⁻²) and MWCNTs films (60.7 mA mM⁻¹ cm⁻²). Finally, the flow injection analysis (FIA) has been used for the amperometric detection of p-acetamidophenol at MWCNTs-PANIFAD film modified screen printed carbon electrode. The sensitivity value of MWCNTs-PANIFAD film (3.3 mA mM⁻¹ cm⁻²) in FIA is also higher than the value obtained for MWCNTs film (1.1 mA mM⁻¹ cm⁻²).     

An electrochemiluminescent biosensor for glucose based on the electrochemiluminescence of luminol on the nafion/glucose oxidase/poly(nickel(II)tetrasulfophthalocyanine)/multi-walled carbon nanotubes modified electrode

A poly(nickel(II) tetrasulfophthalocyanine)/multi-walled carbon nanotubes composite modified electrode (polyNiTSPc/MWNTs) was fabricated by electropolymerization of NiTSPc on MWNTs-modified glassy carbon electrode (GCE). The modified electrode was found to be able to greatly improve the emission of luminol electrochemiluminescence (ECL) in a solution containing hydrogen peroxide. Glucose oxidase (GOD) was immobilized on the surface of polyNiTSPc/MWNTs modified GC electrode by Nafion to establish an ECL glucose sensor. Under the optimum conditions, the linear response range of glucose was 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ with a detection limit of 8.0 × 10⁻⁸ mol L⁻¹ (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The ECL sensor showed an outstanding well reproducibility and long-term stability. The established method has been applied to determine the glucose concentrations in real serum samples with satisfactory results.     

Nonenzymatic sensing of glucose using a carbon ceramic electrode modified with a composite film made from copper oxide,overoxidized polypyrrole and multi-walled carbon nanotubes

Microchimica Acta - A carbon ceramic electrode was modified with a thin film composed of overoxidized polypyrrole, CuO and multi-walled carbon nanotubes. The surface morphology, electrochemical...