Carbon nanotube (CNT) fibers have been used to fabricate microelectrodes with an attractive electrochemical behavior. By combining the advantages of CNT materials and fiber microelectrodes, the new material expands the scope of CNT-based electrochemical devices. The CNT fiber offers a marked decrease in the overvoltage for the NADH, dopamine, and hydrogen peroxide and circumvents NADH surface fouling effects. Heat treatment is shown to be extremely useful for activating the CNT fiber surfaces for electron transfer. SEM imaging and cyclic-voltammetric data indicate that the heat treatment leads to the removal of nonconducting residues and exposure of a "fresh" CNT surface. The new electrode material thus presents new opportunities for a wide range of electrochemical and analytical applications.

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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.

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A single carbon fiber microelectrode modified with multi-wall carbon nanotubes (MWCNT) and Nafion exhibits an attractive electroanalytical performance for enhanced voltammetric detection of dopamine in the presence of ascorbate at physiological pH. The fast and simple preparation protocol involves dipping a single carbon fiber microelectrode into a modification solution containing Nafion and MWCNT. The resulting surface modification couples the sensitivity improvement associated with the MWCNT with the permselectivity of Nafion films. The microsensor displays highly linear behavior over the 2 to 20 mM dopamine range examined (R of 0.997), with a detection limit of 70 nM. A highly reproducible response was observed for 50 repetitive measurements with a RSD of 1.6%, while the effect of ascorbate upon the voltammetric signal for dopamine was negligible. In addition, some more insights are given into the electroanalytical performance of the MWCNT/Nafion modified microelectrode. Such a disposable dopamine microsensor holds great promise for convenient detection of dopamine in the presence of ascorbate at physiological concentrations in microvolume samples and at microlocations (e.g., measurement of dopamine under physiological conditions).

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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).

Carbon-nanotube modified glassy-carbon electrodes are used for enhancing the stability and sensitivity of voltammetric and amperometric measurements of phenolic compounds. Cyclic voltammetric experiments indicate that the redox process involves the formation of a surface-confined layer that promotes (rather than inhibits) the phenol oxidation. The amperometric response of the coated electrodes is highly stable, with 85% of the initial activity remaining after 30 min stirring of a 2 Â 10 À4 M phenol solution (compared to complete inhibition of the redox process within 6 min at the bare surface). Similar stability improvements were observed for different phenolic compounds and different concentrations of such compounds. The modified electrodes display greatly enhanced current signals in cyclic voltammetric and amperometric experiments.