Highly sensitive composite electrode based on electrospun carbon nanofibers and ionic liquid

A novel composite electrode has been developed using electrospun carbon nanofibers (CNF) and the ionic liquid 1-butyl-4-methylpyridinium hexaflurophosphate (PFP). The highly pure CNF without any pretreatment exhibited very low background noise and high voltammetric responses. When applied to sensing of biomolecules under physiological conditions, the CNF/PFP electrode provided attractive electrochemical performances, such as high sensitivity and good selectivity for simultaneous detection of dopamine, ascorbic acid and uric acid, guanine and adenine, as well as high signal-to-noise ratio and good stability for amperometric detection of NADH.     

A nonenzymatic sensor for xanthine based on electrospun carbon nanofibers modified electrode

Xanthine (Xa) determination is of considerable importance in clinical analysis and food quality control. Therefore, a sensitive nonenzymatic amperometric sensor for Xa based on carbon nanofibers (CNFs) has been proposed. The CNFs, which were prepared by electrospinning technique and subsequent thermal treatment, were used to modify carbon paste electrode (CNF-CPE) to construct the amperometric sensor device without any oxidation pretreatment. In application to Xa electrochemical determination, the CNF-CPE exhibited high electrocatalytic activity and fast amperometric response. Various experimental parameters, such as pH and applied potential were optimized. Under the optimal conditions, the dynamic linear range of Xa was 0.03-21.19 μM (R = 0.9992) with the detection limit low to 20 nM (S/N = 3). With good selectivity and sensitivity, the present system was successfully applied to estimate the freshness of fish and determine Xa in human urine, which provides potential application in food quality control and clinical analysis.     

Electrochemical Detection of Hydrazine Based on Electrospun Palladium Nanoparticle/Carbon Nanofibers

In this work, we developed an electrochemical method for the detection of hydrazine based on palladium nanoparticle/carbon nanofibers (Pd/CNFs). Pd/CNFs were prepared by electrospinning technique and subsequent thermal treatments. The electrocatalytic behaviors of Pd/CNFs modified glassy carbon electrode (Pd/CNF‐GCE) for hydrazine oxidation were evaluated by cyclic voltammetry (CV), an obvious and well‐defined oxidation peak appeared at ?0.32 V (vs. Ag/AgCl). The mechanism of the oxidation of hydrazine at Pd/CNF‐GCE was also studied, which demonstrated an irreversible diffusion‐controlled electrode process and a four‐electron transfer involved in the overall reaction. Furthermore, the wide linear range, low detection limit, good reproducibility and excellent storage stability were obtained utilizing differential pulse voltammetry (DPV).     

Application of Carbon Paste Electrode Modified with Carbon Nanofibres/Polyaniline/Platinum Nanoparticles as an Electrochemical Sensor for the Determination of Bezafibrate

The present study deals with the development of an electrochemical sensor for quantitative determination of Bezafibrate (BZF) based on carbon nanofibers/polyaniline/platinum nanoparticles modified carbon paste electrode (CNF/PANI/Pt/CPE). BZF is a fibric acid derivative and is used largely in the treatment of lipid disorders. The nanocomposite was synthesized by in situ polymerization of aniline using ammonium persulphate and platinum nanoparticles were uniformly decorated on the CNF/PANI surface by reducing hexachloroplatinic acid using sodium borohydride. The electrochemical response of BZF at CNF/PANI/Pt/CPE was studied using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The above study resulted into significant improvement of the electrochemical signal towards the oxidation of BZF, revealing that the oxidation process is highly favorable at the surface of modified electrode. The anodic peak current I_p (μA) is found to be linearly dependent on BZF concentration in the range of 0.025 μM to 100 μM with a detection limit of 2.46 nM. The practical analytical utilities of the sensor were investigated by performing the experiments on synthetic pharmaceutical formulations, human blood serum and urine samples which offered good recovery, suggesting the high efficacy and authenticity of CNF/PANI/Pt/CPE sensor for BZF determination.     

Amperometric NADH Biosensor Based on Magnetic Chitosan Microspheres/Poly(thionine) Modified Glassy Carbon Electrode

Novel magnetic chitosan‐coated microspheres (MCMSs) were prepared by modifying carbon‐coated iron magnetic nanoparticles with chitosan. An amperometric dihydronicotinamide adenine dinucleotide (NADH) sensor was constructed based on immobilizing MCMS on the surface of a polythionine (PTH) modified glassy carbon electrode (GCE). The fabrication of MCMS/PTH film and its electrocatalytic effect on electrochemical oxidation of NADH were investigated by electrochemical impedance spectroscopy (EIS) and voltammetric methods. It was found that the resulting integrated films of PTH and MCMS exhibit high electrocatalytic response to NADH by significantly reduce its overpotential. The effects of the experimental variables on the amperometric determination of NADH such as solution pH and working potential were investigated for optimum analytical performance. This electrochemical sensor had a fast response to NADH which was less than 10 s. Linear response ranges of 2–10 μM and 10–100 μM and a detection limit of 0.51 μM (S/N=3) were obtained under the optimum conditions. Moreover, the selectivity, stability and reproducibility of this biosensor was evaluated with satisfactory results.     

Carbon nanofiber vs. carbon microparticles as modifiers of glassy carbon and gold electrodes applied in electrochemical sensing of NADH

Carbon materials (CMs), such as carbon nanotubes (CNTs), carbon nanofibers (CNFs), and carbon microparticles (CMPs) are used as doping materials for electrochemical sensors. The efficiency of these materials (either before or after acidic treatments) while being used as electrocatalysts in electrochemical sensors is discussed for β-nicotinamide adenine dinucleotide (NADH) detection using cyclic voltammetry (CV). The sensitivity of the electrodes (glassy carbon (GC) and gold (Au)) modified with both treated and untreated materials have been deeply studied. The response efficiencies of the GC and Au electrodes modified with CNF and CMP, using dimethylformamide (DMF) as dispersing agent are significantly different due to the peculiar physical and chemical characteristics of each doping material. Several differences between the electrocatalytic activities of CMs modified electrodes upon NADH oxidation have been observed. The CNF film promotes better the electron transfer of NADH minimizing the oxidation potential at +0.352 V. Moreover higher currents for the NADH oxidation peak have been observed for these electrodes. The shown differences in the electrochemical reactivities of CNF and CMP modified electrodes should be with interest for future applications in biosensors.     

Electrochemical determination of L-Tryptophan, L-Tyrosine and L-Cysteine using electrospun carbon nanofibers modified electrode

A novel and simple method for the direct and quantitative determination of L-tryptophan (Trp), L-tyrosine (Tyr) and L-cysteine (Cys) was proposed in this work. Carbon nanofibers (CNFs), made by electrospinning technique, were used to modify carbon paste electrode (CPE) without any treatment to study the electrochemical behaviors of the three amino acids using cyclic voltammetry (CV) and constant potential amperometric method. The results demonstrated that the CNFs modified carbon paste electrode (CNF-CPE) exhibited high electrocatalytic activity and good analytical performance towards the oxidation of the three amino acids. The linear ranges of Trp, Tyr and Cys were 0.1-119, 0.2-107 and 0.15-64 μM with correlation coefficients of 0.9994, 0.9985 and 0.9996, respectively. All the detection limits of the analytes were 0.1 μM (S/N = 3). In addition, the CNF-CPE displayed good reproducibility, high sensitivity and good selectivity towards the determination of the amino acids, making it suitable for the determination of Trp, Tyr and Cys in clinical and medicine.     

Direct Determination of Paracetamol in Environmental Samples Using Screen‐printed Carbon/Carbon Nanofibers Sensor – Experimental and Theoretical Studies

The paper describes the first electrochemical method (differential pulse adsorptive stripping voltammetry, DPAdSV) using a screen‐printed sensor with a carbon/carbon nanofibers working electrode (SPCE/CNFs) for the direct determination of low (real) concentrations of paracetamol (PA) in environmental water samples. By applying this sensor together with DPAdSV, two linear PA concentration ranges from 2.0×10^?9 to 5.0×10^?8 mol L^?1 (r=0.9991) and 1.0×10^?7–2.0×10^?6 mol L^?1 ( r=0.9994) were obtained. For the accumulation time of 90 s, the limit of detection was 5.4×10^?10 mol L^?1. Moreover, the SPCE/CNFs sensor and the DPADSV procedure for PA determination are potentially applicable in field analysis. The process of PA adsorption at the SPCE/CNFs surface was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and theoretical studies. In the theoretical study of the interaction of CNF and PA, the first species was modelled by graphene‐like clusters containing up to 37 rings. It was found that the preferable orientation of PA is parallel to the carbon surface with the binding energy of about ?68 kJ/mol calculated by symmetry‐adapted perturbation theory (SAPT). Both the selectivity and the accuracy of the developed sensor for real sample analysis were also investigated using Polish river and sea samples.     

基于表面活性剂单分子层修饰碳糊电极的一氧化氮电化学传感器及其应用

报道了一种表面活性剂单分子层修饰碳糊电极,并用于NO的高灵敏电化学检测。研究表明,表面活性剂通过烷基链在电极表面形成的疏水性单分子层微环境对NO的电化学响应具有较好的促进作用。其中,阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)对NO的电化学氧化表现出最强的催化活性和增敏作用。在Nafion膜覆盖的CTAB修饰碳糊电极上,NO的安培响应与其浓度在3.6×10-8～1.8×10-5mol/L范围内呈良好的线性关系,检出限为1.8×10-8mol/L。该电极作为低成本、高灵敏的NO电化学传感器,被成功应用于大鼠肺组织细胞中NO释放的实时监测。     

Ruthenium Nanoparticles on Nano‐Level‐Controlled Carbon Supports as Highly Effective Catalysts for Arene Hydrogenation

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with [Ru₃(CO)₁₂] in toluene heated at reflux provided the corresponding CNF‐supported ruthenium nanoparticles, Ru/CNFs (Ru content=1.1–3.8 wt %). TEM studies of these Ru/CNFs revealed that size‐controlled Ru nanoparticles (2–4 nm) exist on the CNFs, and that their location was dependent on the surface nanostructures of the CNFs: on the edge of the graphite layers (CNF‐P), in the tubes and on the surface (CNF‐T), and between the layers and on the edge (CNF‐H). Among these Ru/CNFs, Ru/CNF‐P showed excellent catalytic activity towards hydrogenation of toluene with high reproducibility; the reaction proceeded without leaching of the Ru species, and the catalyst was reusable. The total turnover number of the five recycling experiments for toluene hydrogenation reached over 180 000 (mol toluene) (mol Ru)^?1. Ru/CNF‐P was also effective for the hydrogenation of functionalized benzene derivatives and pyridine. Hydrogenolysis of benzylic C? O and C? N bonds has not yet been observed. Use of poly(ethylene glycol)s (PEGs) as a solvent made possible the biphasic catalytic hydrogenation of toluene. After the reaction, the methylcyclohexane formed was separated by decantation without contamination of the ruthenium species and PEG. The insoluble PEG phase containing all of the Ru/CNF was recoverable and reusable as the catalyst without loss of activity.     

Flow Injection Analysis of Maleic Hydrazide Using an Electrochemical Sensor Based on Palladium‐Dispersed Carbon Paste Electrode

A new analytical methodology for the electrochemical detection of the herbicide maleic hydrazide (3,6‐dihydroxypyridazine) by flow injection analysis is presented. This method is supported by the novel application of a palladium‐dispersed carbon paste electrode as an amperometric sensor for this herbicide. Maleic hydrazide shows anodic electrochemical activity on carbon‐based electrodes (glassy carbon or carbon paste electrodes) in all the pH range. This electrochemical activity is enhanced using metal‐dispersed carbon paste electrodes, especially at Pd‐dispersed CPE which displays good oxidation signals at 690 mV (0.050 M phosphate buffer pH 7.0), 140 mV lower than at unmodified electrodes. Under the optimized conditions, the electroanalytical performance of Pd‐dispersed CPE in flow injection analysis was excellent, with good reproducibility (RSD 3.3%) and a wide linear range (1.9×10^?7 to 1.0×10^?4 mol L^?1). A detection limit of 1.4×10^?8 mol L^?1 (0.14 ng maleic hydrazide) was obtained for a sample loop of 100 μL at a fixed potential of 700 mV in 0.050 M phosphate buffer solution at pH 7.0 and a flow rate of 2.0 mL min^?1. The proposed method was applied for the maleic hydrazide detection in natural drinking water samples.     

An Electrochemical Sensor Based on Nitrogen‐doped Carbon Nanofiber for Bisphenol A Determination

In this paper, bisphenol A was determined by electrochemical method at a nitrogen‐doped carbon nanofiber modified carbon paste electrode (NCNF/CPE) with high sensitivity and good selectivity. NCNF was obtained by a simple electrospinning followed by carbonization procedure, in which polyacrylonitrile (PAN) as precursor and nitrogen doping was realized by re‐utilizing the tail gas that produced in the thermal pretreatment process. Good reproducibility and high stability were obtained for BPA detection at NCNF modified CPE. Current response plotted with BPA concentration was linear in the range of 0.1–60 μM with LOD of 0.05 μM. The proposed electrochemical sensor was employed for BPA determination with satisfactory recoveries for real water samples, indicating the practical applicability of NCNF/CPE.     

Carbon nanofibers decorated with platinum nanoparticles: a novel three-dimensional platform for non-enzymatic sensing of hydrogen peroxide

We have developed a 3-dimensional (3-D) electrochemical sensor for highly sensitive detection of hydrogen peroxide (H₂O₂). Porous 3-D carbon nanofibers (CNFs), prepared by electrospinning, served as scaffold on a glassy carbon electrode. The 3-D CNFs were functionalized with platinum nanoparticles (Pt-NPs) by in-situ gas-phase decomposition of platinum salts at high temperature. The Pt-NPs act as an electrocatalyst for the decomposition of H₂O₂. TEM revealed that large amounts of Pt-NPs are deposited in the electrospun CNFs electrode even without using any stabilizer or reducing reagent. The sensor was investigated by cyclic voltammetry and amperometry and displays a good response to H₂O₂ with a linear range between 10 μM and 15 mM (R?=?0.9994), a low detection limit (3.4 μM at a signal-to-noise ratio of 3), and a response time of 3 s. The sensor shows excellent stability and selectivity.

Comparison of the Electrochemical Reactivity of Electrodes Modified with Carbon Nanotubes from Different Sources

The electrochemical activity of five different commercial carbon nanotubes (CNT), prepared by the ARC discharge and chemical vapor deposition (CVD) methods, has been assessed and compared. The various multi‐walled CNT were immobilized onto a glassy carbon electrode using three different dispersing agents (Nafion, concentrated nitric acid and dimethylformamide (DMF)) and their voltammetric response to ferricyanide, NADH and hydrogen peroxide examined. SEM was used to characterize the surface morphology. The corresponding cyclic voltammetry and amperometric data showed that the electrocatalytic activity, the background current and the electroanalytical performance are strongly depended on the preparation of the CNT and on the dispersing agent used. The most favorable amperometric detection of NADH and hydrogen peroxide is observed at the NanoLab CVD‐produced CNT in connection to a DMF‐surface dispersion. ARC‐produced CNT display a smaller capacitance, particularly in connection to the DMF dispersion. Such differences in the electrochemical reactivity are attributed to the different surface chemistries (primarily defect densities) of the corresponding CNT layers, associated with the different production and dispersion protocols.     

Enhanced Electron Transfer Rates by AC Voltammetry for Ferrocenes Attached to the End of Embedded Carbon Nanofiber Nanoelectrode Arrays

The effect of the interior structure of carbon nanomaterials on their electrochemical properties is not well understood. We report here the electron transfer rate (ETR) of ferrocene (Fc) molecules covalently attached to the exposed end of carbon nanofibers (CNFs) in an embedded nanoelectrode array. The ETR in normal DC voltammetry was found to be limited by the conical graphitic stacking structure interior of CNFs. AC voltammetry, however, can cope with this intrinsic materials property and provide over 100 times higher ETR, likely by a new capacitive pathway. This provides a new method for high‐performance electroanalysis using CNF nanoelectrodes.     

SE‐30 Graphite Composite Electrode: An Alternative for the Development of Electrochemical Biosensors

A new graphite composite electrode was constructed by mixing graphite powder with chromatography stationary phase, SE‐30, as the binder. The electrochemical behavior of the new electrode has been evaluated and compared with that of traditional carbon paste electrode (CPE). The proposed electrode provides a remarkable increase in the rate of electron transfer of biomolecules such as nicotinamide adenine dinucleotide (NADH), cysteine, ascorbic acid and catechol and shows a low surface fouling effects. The electrode shows highly promising results when used as an amperometic sensor for biocompounds such as NADH.     

Fast preparation of PtRu catalysts supported on carbon nanofibers by the microwave-polyol method and their application to fuel cells

PtRu alloy nanoparticles (24 +/- 1 wt %, Ru/Pt atomic ratios = 0.91-0.97) supported on carbon nanofibers (CNFs) were prepared within a few minutes by using a microwave-polyol method. Three types of CNFs with very different surface structures, such as platelet, herringbone, and tubular ones, were used as new carbon supports. The dependence of particles sizes and electrochemical properties on the structures of CNFs was examined. It was found that the methanol fuel cell activities of PtRu/CNF catalysts were in the order of platelet > tubular > herringbone. The methanol fuel cell activities of PtRu/CNFs measured at 60 degrees C were 1.7-3.0 times higher than that of a standard PtRu (29 wt %, Ru/Pt atomic ratio = 0.92) catalyst loaded on carbon black (Vulcan XC72R) support. The best electrocatalytic activity was obtained for the platelet CNF, which is characterized by its edge surface and high graphitization degree.     

All‐Polystyrene 3D‐Printed Electrochemical Device with Embedded Carbon Nanofiber‐Graphite‐Polystyrene Composite Conductor

Carbon nanofibres (CNFs) and graphite flake microparticles were added to thermoplastic polystyrene polymer with the aim of making new conductive blends suitable for 3D‐printing. Various polymer/carbon blends were evaluated for suitability as printable, electroactive material. An electrically conducting polystyrene composite was developed and used with commercially available polystyrene (HIPS) to manufacture electrodes suitable for electrochemical experiments. Electrodes were produced and evaluated for cyclic voltammetry of aqueous 1,1’‐ferrocenedimethanol and differential pulse voltammetry detection of aqueous Pb²⁺ via anodic stripping. A polystyrene/CNF/graphite (80/10/10 wt%) composite provides good conductivity and a stable electrochemical interface with well‐defined active geometric surface area. The printed electrodes form a stable interface to the polystyrene shell, give good signal to background voltammetric responses, and are reusable after polishing.     

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。     

Chemoselective Hydrogenation of Functionalized Nitroarenes and Imines by Using Carbon Nanofiber‐Supported Iridium Nanoparticles

The reaction of three types of carbon nanofibers (CNFs; platelet: CNF‐P, tubular: CNF‐T, herringbone: CNF‐H) with Ir₄(CO)₁₂ in mesitylene at 165 °C provided the corresponding CNF‐supported iridium nanoparticles, Ir/CNFs (Ir content=2.3–2.6 wt. %). Transmission electron microscopy (TEM) studies of these Ir/CNF samples revealed that size‐controlled Ir nanoparticles (average particle size of 1.1–1.5 nm) existed on the CNFs. Among the three Ir/CNF samples, Ir/CNF‐T showed an excellent catalytic activity and chemoselectivity towards hydrogenation of functionalized nitroarenes and imines; the corresponding aniline derivatives were obtained with high turnover numbers at ambient temperature under 10 atm of H₂, and the catalyst is reusable. Ir/CNF‐T was also effective for the reductive N‐alkylation of anilines with carbonyl compounds.