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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]

Single walled carbon nanotube (SWNT) network electrodes, in which a planar arrangement of SWNTs on an inert surface serve as a working electrode for voltammetry, offer considerable attributes for electroanalysis. Here, the effect of SWNT network density on the trace voltammetric analysis of a water-soluble ferrocene derivative (FcCOOH) is investigated in the presence of polyethylene glycol (PEG) or albumin, species that can foul (block) an electrode via adsorption. Fc-based analytes typically find use in redox labelling or redox shuttling, point-of-care electrochemical detection devices. Comparison is made between SWNT electrodes, grown by catalyzed chemical vapour deposition at three different surface coverages, 5, ~20 and ~30 μm SWNT μm-2, and commercial screen-printed carbon electrodes (SPCEs). In the presence of PEG (8% 2 K), for cyclic voltammetry, the lowest detectable concentration decreases as SWNT network density decreases. However, when employing differential pulse voltammetry, all three networks show a 1 nM FcCOOH limit of detection, three orders of magnitude smaller than achievable with SPCEs. This is attributed to the low capacitance of the SWNTs and absence of amorphous carbon structures which can contribute a pseudo-capacitive response. For both polyethylene glycol (PEG) and albumin (4%), repeat cycling shows the higher density SWNT network electrodes (≥20 μm SWNT μm-2) are far less susceptible to electrode fouling. Toward practical devices, a three-electrode chip, similar in design to that used in SPCEs, but using high density SWNT network electrodes, is also demonstrated to have impressive detection sensitivity for FcCOOH (nM level) in PEG solutions. The simplicity and practicality of the design widens the potential applications of these ultra-sensitive diagnostic tools based on planar network SWNTs. Comparison of single-walled carbon nanotube network and commercially available screen-printed carbon electrode for trace level electrochemical detection in biological media. Unlabelled Image [ABSTRACT FROM AUTHOR]