Electrochemical sensing of bisphenol A on single-walled carbon nanotube paper electrodes

The electrochemical detection of BPA often requires modification of electrodes to overcome BPA′s slower kinetics and higher oxidation potential. This work reports a modification-free, paper electrode based on vacuum-filtered SWCNT thin film. The prepared electrode does not need to be polished or transferred into the conducting substrates. The linear sweep voltammetric detection showed a linear response from 0.5–10 μM and 25–100 μM with the experimental LOD of 1.0 μM (S/N=3). The interference study and good recovery percentage (93–105 %) in real water samples demonstrated the method‘s selectivity. The sensor can be promising for developing a simple, low-cost, portable, and paper-based BPA monitoring system.     

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.     

Metallic impurity free carbon nanotube paste electrodes

Electrodes modified with carbon nanomaterials find wide ranging applications in electrochemistry such as in energy generation and storage through to applications in electroanalysis. A substantial limitation is the presence of metallic impurities which vary between batches and can produce erroneous results. Consequently we have explored the electrochemical properties of metallic impurity free carbon nanotube paste electrodes using potassium ferrocyanide and hydrogen peroxide as model compounds. In terms of the latter utilising cyclic voltammetry, a linear range from 0.75 to 3 mM with a limit of detection of 0.19 mM is possible using the electrochemical oxidation of hydrogen peroxide while using the electrochemical reduction of the target analyte, a linear range from 0.5 to 249 mM is possible with a detection limit of 0.43 mM.The ultra-small size of the carbon nanotubes and fabrication methodology result in a tightly bound carbon nanotube electrode surface which does not exhibit thin-layer behaviour resulting in highly reproducible electrodes with the %RSD found to be 5.5%. These analytical ranges, detection limits and reproducibility are technologically useful.The carbon nanotubes utilised are completely free from metallic impurities and do not require lengthy processing to remove impurities and consequently have no variation in the purity of the nanomaterial between batches as is commonly the case for other available carbon nanotube material. The impurity free nature of this nanomaterial allows for highly reproducible and intelligent sensors based on carbon nanotubes to be understood and realised for the first time.     

Lithium-ion batteries based on vertically-aligned carbon nanotube electrodes and ionic liquid electrolytes

In conjunction with environmentally benign ionic liquid electrolytes, vertically-aligned carbon nanotubes (VA-CNTs) sheathed with and without a coaxial layer of vanadium oxide (V(2)O(5)) were used as both cathode and anode, respectively, to develop high-performance and high-safety lithium-ion batteries. The VA-CNT anode and V(2)O(5)-VA-CNT cathode showed a high capacity (600 mAh g(-1) and 368 mAh g(-1), respectively) with a high rate capability. This led to potential to achieve a high energy density (297 Wh kg(-1)) and power density (12 kW kg(-1)) for the prototype batteries to significantly outperform the current state-of-the-art Li-ion batteries.     

Vertically aligned carbon nanotube based electrodes: Fabrication, characterisation and prospects

We present a methodology to fabricate carbon nanotube based electrodes using plasma enhanced chemical vapour deposition. The metal catalyst nanoparticles used to promote nanotube growth are removed using a water plasma treatment in combination with an acid attack. The final integrated microelectrode-based devices present excellent electrocatalytic properties that make them suitable for electrochemical applications. The presented methodology enables the construction of highly regular and dense vertically aligned carbon nanotube (VACNT) forests that can be confined within the patterned bounds of a desired surface. These VACNT electrodes display very low capacitive currents and are amenable to further chemical modifications.     

Detection of homocysteine at carbon nanotube paste electrodes

The use of a carbon-nanotube paste (CNTP) electrode provides an effective means for the determination of homocysteine. A decrease of ca. 120 mV in the overpotential for the oxidation of homocysteine compared to a traditional carbon paste electrode, is reported along with greatly enhanced signal-to-noise characteristics. The analytical parameters have been assessed with a linear range from 5 to 200 μM and a detection limit of 4.6 μM. Furthermore, the generic nature of this increased reactivity of the CNTP surface towards thiol moieties has been demonstrated with cysteine, glutathione and n-acetylcysteine, providing a greatly enhanced electrochemical response compared to the carbon paste electrode.     

Covalent immobilization of oligonucleotides on p-aminophenyl-modified carbon screen-printed electrodes for viral DNA sensing

DNA-sensing platforms were prepared by covalently attaching oligonucleotide capture probes onto p-aminophenyl-functionalized carbon surfaces and applied to the determination of an amplified herpes virus DNA sequence in an electrochemical hybridization assay.     

Electro-desalination of saline solutions by multiwall carbon nanotube electrodes

Electrodes of multiwall carbon nanotube (MWCNT) with polytetrafluoroethylene (PTFE) binding were prepared for NaCl removal from water in the electrosorption system. SEM, XRD and BET analysis were used to characterize the prepared electrodes. The optimum electrosorption parameters (electrosorption temperature, NaCl concentration, electrosorption time, and potential) were studied. The maximum electrosorption capacity (15.64 mg/g) was obtained at −1.0 V, 100 min, and 30 °C. The electrosorption capacity of electrodes decreased from 15.64 mg/g to 6.15 mg/g with the temperature rise from 30 to 50 °C. Also, the kinetics of electrosorption NaCl by Electrodes was investigated by pseudo-first-order and pseudo-second-order. The results indicated that the electrosorption data will fit with the pseudo-first-order model indicating the physio-electrosorption of NaCl by Electrodes with activation energy was 19.45 kJ mol⁻¹. The regeneration result indicated the exceptional and stable reusability of MWCNT/PTFE in the NaCl electrosorption system.     

Development of a microbial biosensor based on carbon nanotube (CNT) modified electrodes

Pseudomonas putida DSM 50026 cells were used as the biological component and the measurement was based on the respiratory activity of the cells estimated from electrochemical measurements. The cells were immobilised on carbon nanotube (CNT) modified carbon paste electrodes (CPE) by means of a redox osmium polymer, viz. poly(1-vinylimidazole)₁₂-[Os-(4,4′-dimethyl-2,2′-dipyridyl)₂Cl₂]^2+/+. The osmium polymer efficiently shuttles electrons between redox enzymes located in the cell wall of the cells and promotes a stable binding to the electrode surface. The effect of varying the amounts of CNT and osmium polymer on the response to glucose was investigated to find the optimum composition of the sensor. The effects of pH and temperature were also examined. After the optimisation studies, the system was characterised by using glucose as substrate. Moreover, the microbial biosensor was also prepared by using phenol adapted bacteria and then, calibrated to phenol. After that, it was applied for phenol detection in an artificial waste water sample.     

Fabrication and study of supercapacitor electrodes based on oxygen plasma functionalized carbon nanotube fibers

Dry-spun Carbon Nanotube(CNT) fibers were surface-modified by atmospheric pressure oxygen plasma functionalization using a well controlled and continuous process. The fibers were characterized by scanning electron microscopy(SEM), Raman spectroscopy, and X-ray Photoelectron Spectroscopy(XPS). It was found from the conducted electrochemical measurements that the functionalized fibers showed a 132.8%increase in specific capacitance compared to non-functionalized fibers. Dye-adsorption test and the obtained Randles-Sevcik plot demonstrated that the oxygen plasma functionalized fibers exhibited increased surface area. It was further established by Brunauer-Emmett-Teller(BET) measurements that the surface area of the CNT fibers was increased from 168.22 m~2/g to 208.01 m~2/g after plasma functionalization. The pore size distribution of the fibers was also altered by this processing. The improved electrochemical data was attributed to enhanced wettability, increased surface area, and the presence of oxygen functional groups, which promoted the capacitance of the fibers. Fiber supercapacitors were fabricated from the oxygen plasma functionalized CNT fiber electrodes using different electrolyte systems. The devices with functionalized electrodes exhibited excellent cyclic stability(93.2% after 4000 cycles), flexibility, bendability, and good energy densities. At 0.5 m A/cm~2, the EMIMBF4 device revealed a specific capacitance, which is 27% and 65% greater than the specific capacitances of devices using EMIMTFSI and H_2 SO_4 electrolytes,respectively. The practiced in this work plasma surface processing can be employed in other applications where fibers, yarns, ribbons, and sheets need to be chemically modified.     

Surface preparation of glassy carbon electrodes

Recent work on glassy carbon electrodes for various applications is reviewed. Activation of glassy carbon electrodes by different types of polishing, heat treatment, and electrochemical methods yields enhanced rates of electron transfer. Characterization of different glassy carbon surfaces by x-ray photoelectron spectroscopy shows that polished and electrochemically pretreated surfaces contain more oxygen on the surface than do unactivated surfaces; much of this oxygen is associated with phenolic groups. Causes of activation, characterization of glassy carbon by spectroscopic methods, and the role of surface cleanliness are summarized. For simple electron-transfer reactions, removal of contaminants from the electrode surface is important. For proton-coupled electrode reactions, specific interactions of reactants with catalytic groups created on the surface during polishing tend to play an important role in electrode activation     

Electrochemical detection of amino acids at carbon nanotube and nickel-carbon nanotube modified electrodes

The oxidation and enhanced detection of traditionally 'non-electroactive' amino acids at a single-wall carbon nanotube (SWNT) surface and at a nickel hydroxide film electrochemically deposited and generated upon the SWNT layer is reported. Different CNT are compared, with Nafion-dispersed SWNT offering the most favorable layer for constant-potential amperometric detection. Factors affecting the oxidation process, including the pH or applied potential, are assessed. The response of the SWNT-Nafion coated electrode compares favorably with that of copper and nickel disk electrodes under flow injection analysis (FIA) conditions. The electrodeposition of nickel onto the SWNT-Nafion layer (Ni-CNT) led to a dramatic enhancement of the analytical response (vs. that observed at the SWNT or nickel electrodes alone). The oxidative process at the Ni(OH)(2) layer has been studied and the increase in sensitivity rationalized. In the presence of amino acid the Ni-CNT layer undergoes an electrocatalytic process in which the amino acid reduces the newly formed NiO(OH) species. Furthermore, the attractive response of both the CNT and Ni-CNT layers has allowed these electrodes to be used for constant-potential FIA of various amino acids and indicates great promise for monitoring chromatographic effluents. Once again an improved signal was observed at the Ni-CNT electrode compared to nickel deposited upon a bare glassy carbon electrode (Ni-GC).     

Electrochemical parameters of ethamsylate at multi-walled carbon nanotube modified glassy carbon electrodes

In this paper, some electrochemical parameters of ethamsylate at a multi-walled carbon nanotube modified glassy carbon electrode, such as the charge number, exchange current density, standard heterogeneous rate constant and diffusion coefficient, were measured by cyclic voltammetry, chronoamperometry and chronocoulometry. The modified electrode exhibits good promotion of the electrochemical reaction of ethamsylate and increases the standard heterogeneous rate constant of ethamsylate greatly. The differential pulse voltammetry responses of ethamsylate were linearly dependent on its concentrations in a range from 2.0 x 10(-6) to 6.0 x 10(-5) mol L(-1), with a detection limit of 4.0 x 10(-7) mol L(-1).     

All-organic actuator fabricated with single wall carbon nanotube electrodes

Compliant electrodes to replace conventional metal electrodes have been required for many actuators to relieve the constraint on the electroactive layer. Many conducting polymers have been proposed for the alternative electrodes, but they still have a problem of poor thermal stability. This article reports a novel all- organic actuator with single wall carbon nanotube (SWCNT) films as an alternative electrode. The SWCNT film was obtained by filtering a SWCNT solution through an anodized alumina membrane. The conductivity of the SWCNT film was about 280 S/cm. The performance of the SWCNT film electrode was characterized by measuring the dielectric properties of NASA Langley Research Center – Electroactive Polymer (LaRC-EAP) sandwiched by the SWCNT electrodes over a broad range of temperature (from 25 to 280 °C) and frequency (from 1 kHz to 1 MHz). The all-organic actuator with the SWCNT electrodes showed a larger electric field-induced strain than that with metal electrodes, under identical measurement conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2532–2538, 2008     

Three-dimensional manganese dioxide-functionalized carbon nanotube electrodes for electrochemical supercapacitors

Three-dimensional manganese dioxide (MnO₂)-functionalized multiwalled carbon nanotube (MWCNT) electrodes have been produced by a simple and scalable thermal decomposition process. The electrodes are prepared by treating planar MWCNT sheets with manganese(II) nitrate (Mn(NO₃)₂) solution and annealing at low temperature (200–300 °C) and ambient pressure. The morphology, chemical composition, and structure of the resulting matrices have been investigated with scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and X-ray diffraction. Supercapacitors assembled with three-dimensional electrodes exhibit a 14-fold increase in specific capacitance (C _sp) in comparison to those containing pristine, two-dimensional MWCNT electrodes. C _sp varies linearly with Mn(NO₃)₂ thermal decomposition temperature (from 100 to 61 F/g at 0.2 A/g), a trend that is discussed in the context of nitrate reaction chemistry and MWCNT structure. This efficient and promising approach allows for simultaneous enhancement of electrode–electrolyte contact area and incorporation of redox-based charge storage within electrochemical capacitors.     

DNA sensing on glassy carbon electrodes by using hemin as the electrochemical hybridization label

The electrochemical behavior of hemin, an iron complex of porphyrin, on binding to DNA at a glassy carbon electrode (GCE) and in solution, is described. Hemin, which interacts with covalently immobilized calf thymus DNA, was detected by use of a bare GCE, a double-stranded DNA-modified GCE (dsDNA-modified GCE), and a single-stranded DNA-modified GCE (ssDNA-modified GCE), in combination with differential pulse voltammetry (DPV). The structural conformation of DNA was determined from changes in the voltammetric signals acquired on reduction of hemin. As a result of its large steric structure and anionic substitution on its porphyrin plane, hemin intercalates between the base pairs of dsDNA. A scan-rate study for hemin and the dsDNA-hemin complex were also performed to determine the electrochemical behavior of the complex. The partition coefficient was obtained from the peak currents measured when different concentrations of hemin were in the presence of dsDNA. By observing the oxidation signals of guanine, damage to DNA after reaction with hemin at the GCE surface was also detected. The electrochemical detection of hybridization between the covalently immobilized probe and its target sequence was detected by use of hemin. These results demonstrate the use of DNA biosensors in conjunction with hemin for electrochemical detection of hybridization and damage to DNA.     

Surface analysis of plasma-patterned biofunctional hybrid titanate-aminosilane xerogel films

The functionalization and patterning of biomedical materials with enhanced surface activity is a main objective for the development of high-specificity biosensors. The surfaces of sol-gel condensed aminopropyltriethoxysilane-tetraisopropyl orthotitanate hybrid materials have been studied in order to describe the mechanisms that allow the fixation of amino groups. X-ray photoelectron spectra obtained from these surfaces are compared with those coming from the surfaces of plasma-etched coatings. The results show that aminopropyl radicals remain on the surface after room-temperature condensation and that they are drastically removed after partial etching of the coating in an Ar plasma. This confirms that the functionalization is effectively a surface feature and suggests that amino groups may remain at the surface covalently bonded to the original amorphous Si-O- structure. Further evidence of the surface functionalization efficiency is illustrated with contact angle and zeta-potential measurements. It is complementarily proved by confocal microscopy that masked regions conserve their molecular activity and are not affected by the etching process. These facts suggest that these materials could play an active role when incorporated into biosensor devices.     

Self-assembled ultrathin carbon black/carbon nanotube films as electrodes for microsupercapacitors

Journal of Solid State Electrochemistry - The ability to control the morphology of composite thin films is essential to construct networks exhibiting the desired final properties. In this work, we...