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The meniscus-based microcapillary electrochemical method (MCEM) allows electrochemical measurements to be made quickly and easily at a wide range of materials, simply by connecting up the sample of interest as a working electrode and bringing a capillary containing an electrolyte solution and quasi-reference/counter electrode into meniscus contact. In this work, microcapillary-based electrochemical methodology is advanced by introducing a very high aspect ratio carbon fibre ultramicroelectrode (CF-UME) allowing generation/collection and shielding (redox competition) measurements to be made. The experimental concept is demonstrated with the outer sphere (ferrocenylmethyl) trimethylammonium ion (FcTMA +/2+ ) redox mediator on a single walled carbon nanotube (SWNT) network. It is then used to investigate electrochemical reactions on a complex electrode, i.e. a SWNT forest, which is not easily investigated using traditional techniques that would require the electrode material to be physically encapsulated. The technique is most powerful when used to probe the different mechanistic pathways of the oxygen reduction reaction (ORR). This aspect is illustrated through studies on platinum, glassy carbon and SWNT forest electrodes. By platinising the CF-UME, the electrode can be used as a local sensor for the intermediate H 2 O 2 and the O 2 reactant, and it is possible to track the evolving consumption of these species near the working electrode during voltammetric measurements. [ABSTRACT FROM AUTHOR]

Electrochemistry at carbon nanotubes (CNTs) is a large and growing field, but one in which there is still uncertainty about the fundamental activity of CNTs as electrode materials. On the one hand, there are many reports which focus on the favourable electrochemical properties of CNT electrodes, such as enhanced detection sensitivity, electrocatalytic effects and reduced fouling. On the other hand, other studies suggest that CNTs may be no more electroactive than graphitic powder. Furthermore, it has been proposed that the catalytic nanoparticles from which CNTs are formed may dominate the electrochemical characteristics in some instances. A considerable body of the literature presumes that the CNT sidewall is inert and that edge-plane-graphite-like open ends and defect sites are responsible for the electron transfer activity observed. In contrast, studies of well characterised single-walled nanotube (SWNT) electrodes, either as individual tubes or as two-dimensional networks, suggest sidewall activity. This review highlights how the various discrepancies in CNT electrochemistry may have arisen, by taking a historical view of the field and identifying crucial issues that still need to be solved. When assessing the behaviour of CNT electrodes, it is vitally important that careful consideration is given to the type of CNT used (SWNT or multi-walled), the quality of the material (presence of impurities), the effect of chemical processing steps in the fabrication of electrodes and the experimental arrangements adopted. Understanding these key features is an essential requirement to develop a fundamental understanding of CNT electrochemistry, to allow a wide range of electroanalytical applications, and to move the field forward rationally. As part of this process, high resolution electrochemical and electrical imaging techniques are expected to play a significant role in the future, as well as theoretical developments which examine the fundamentals of electron transfer at different types of CNTs and their characteristic surface sites. [ABSTRACT FROM AUTHOR]

The development of atomic force microscopy (AFM) over the past 20 years has had a major impact on materials science, surface science and various areas of biology, and it is now a routine imaging tool for the structural characterization of surfaces. The lateral resolution in AFM is governed by the shape of the tip and the geometry of the apex at the end of the tip. Conventional microfabrication routes result in pyramid-shaped tips, and the radius of curvature at the apex is typically less than 10 nm. As well as producing smaller tips, AFM researchers want to develop tips that last longer, provide faithful representations of complex surface topographies, and are mechanically non-invasive. Carbon nanotubes have demonstrated considerable potential as AFM tips but they are still not widely adopted. This review traces the history of carbon nanotube tips for AFM, the applications of these tips and research to improve their performance. [ABSTRACT FROM AUTHOR]

Abstract: The use of single walled carbon nanotube (SWNT) band electrodes in a channel flow cell, for low concentration detection, with hydrodynamic voltammetry is reported. A two dimensional SWNT network electrode is combined with a one piece channel flow cell unit, fabricated by microstereolithography. This configuration provides well defined hydrodynamics over a wide range of volume flow rates (0.05–25mL min−1). Limiting current measurements, from linear sweep voltammograms, are in good agreement with the channel electrode Levich equation, for the one electron oxidation of ferrocenylmethyl trimethylammonium (FcTMA+), over a wide concentration range, 1×10−8 M to 2.1×10−5 M, with a detection limit of 5nM. At the highest flow rates, some influence of the slightly recessed electrode geometry arising from the SWNT electrode fabrication is noted. However, this can be accounted for by a full simulation of the hydrodynamics and solution of the resulting convection–diffusion equation. Application of this hydrodynamic configuration to the voltammetric detection of dopamine is also demonstrated. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance spectroscopy (EIS), coupled with chemical vapour deposition (CVD) grown single-walled carbon nanotube (SWNT) network disk-shaped ultramicroelectrodes (UMEs), gives stable, very well-defined and highly reproducible EIS responses for electrolysis of a simple outer sphere redox couple (FcTMA+/2+). The resulting EIS data can be fitted accurately using a simple electrical circuit model, enabling information on double-layer capacitance, diffusion coefficient of the electroactive species and the rate constant of ET (k 0) to be extracted in a single EIS experiment. These values are replicated for a range of mediator concentrations and UME sizes (in the range 25–100μm diameter) demonstrating the robustness of the method. These initial studies bode well for impedance based electroanalysis using SWNT network UMEs. [Copyright &y& Elsevier]

The article describes the use of pristine single-walled carbon nanotubes (SWNT), grown in a two-dimensional network arrangement on an inert support, as an electrode material with low background currents, facilitating trace level cyclic voltammetry measurements. According to the authors, electrically connected SWNT networks are produced on insulating surfaces via catalyzed chemical vapor deposition at Fe nanoparticles. They add SWNT offers a simple and useful route to concentration levels.

The electrochemical measurement of dopamine (DA), in phosphate buffer solution (pH 7.4), with a limit of detection (LOD) of ~5 pM in 50 μL (~ 250 attomol) is achieved using a band electrode comprised of a sparse network of pristine single-walled carbon nanotubes (SWNTs), which covers <1% of the insulating substrate. The SWNT electrodes are deployed as amperometric (anodic) detectors in microfluidic cells, produced by microstereolithography, designed specifically for flow injection analysis (FIA). The flow cells, have a channel (duct) geometry, with cell height of 25 μm, and are shown to be hydrodynamically well-defined, with laminar Poiseuille flow. In the arrangement where solution continuously flows over the electrode but the electrode is only exposed to the analyte for short periods of time, the SWNT electrodes do not foul and can be used repeatedly for many months. The LOD for dopamine (DA), reported herein, is significantly lower than previous reports using FIA–electrochemical detection. Furthermore, the SWNT electrodes can be used as grown, i.e., they do not require chemical modification or cleanup. The extremely low background signals of the SWNT electrodes, as a consequence of the sparse surface coverage and the low intrinsic capacitance of the SWNTs, means that no signal processing is required to measure the low currents for DA oxidation at trace levels. DA detection in artificial cerebral fluid is also possible with a LOD of ~50 pM in 50 μL (~2.5 fmol). [ABSTRACT FROM AUTHOR]

Abstract: A field ionization source based on densely spaced, vertically aligned carbon nanotubes (CNTs) has been developed and evaluated. The CNTs contained nickel particles at their tips. This source would be suitable for analytical mass spectrometry. With a positive voltage on the dense CNT arrays, the strong electric field generated around the CNT tips has effected field ionization. The ionization of inert gases, including helium, and organic compounds, including acetone and methane, and the control and the transfer of the resulting ions have been achieved. These results represent a base for application of this new ion source in mass spectrometry. [Copyright &y& Elsevier]