RECEIVED DATE (to be automatically inserted after your manuscript is accepted if requiredaccording to the journal that you are submitting your paper to) CORRESPONDING AUTHOR FOOTNOTE. F. Javier del Campo. Tel.: +34-935.947.700; Fax number: +34-935.801.496.
2ABSTRACT. The diffusion domain approach is a general framework for the understanding, interpretation and prediction of the response of microelectrode arrays. This work exposes some of its limitations, particularly when dealing with nanoelectrode arrays of a few microns in size. This article provides an overview of the principles and assumptions underpinning the diffusion domain approach, and then applies it to the study of nanoelectrode arrays. The apparent disagreement between theory and experimental data, due to the importance of radial diffusion to nanoelectrode arrays compared to microelectrode arrays, is explained using simulations and experiments. The principle that an array of micro-or nano-electrodes eventually behaves as if the entire array were a single electrode of the size of the array, with its corresponding properties, applies always. However, while microelectrode arrays tend to behave as macroelectrodes, nanoelectrode arrays on the other hand may behave as microelectrodes.For the case of arrays of small numbers of electrodes, or array sizes of microns or less in size, this compromises one of the key assumptions of the diffusion domain approach, namely that inner electrodes in an array are equivalent, which may lead the unaware to erroneous conclusions.
Microband electrode arrays are useful tools for the electrochemist, offering the enhanced sensitivity associated
with microelectrodes but with a higher total current output. For optimum performance, the array may be
designed such that space is used efficiently but the individual microbands behave as isolated electrodes on
the time scale of the experiment. For a linear sweep experiment, the optimum specifications of a microband
array depend on the scan rate used and the diffusion coefficient of the electroactive species. A two-dimensional
simulation method is used to examine the nature of the diffusion to a regular array of microbands. Cyclic
voltammetry of hexaammineruthenium(III)chloride is performed at a regularly spaced microband array to
test the theory.
Room temperature ionic liquids (RTILs) have been applied to a microelectrode array and been demonstrated to form effective, membrane-free amperometric gas sensors. Determining the RTIL [P(6,6,6,14)][FAP] as the most appropriate choice for extended use, the amperometric quantification of oxygen has been demonstrated. The response of the sensor was quantified by both cyclic voltammetry and chronoamperometry. A range of O(2) contents (2-13% v/v) and RTIL layer thicknesses (from ca. 6 to 125 mum) have been investigated. The combination of microelectrode array and RTIL, as well as the absence of membrane and volatile solvent, results in an elegant, easy to calibrate gas sensor with potential utility in standard and nonstandard conditions.
This article reviews the literature dealing with electroanalytical applications of ultramicroelectrode arrays over the past twenty years. A brief theoretical description of the mass transport mode governing their behavior is given, after which the main fabrication methods are described. The applications described in the later sections of this review range from conventional electroanalysis, namely trace metal stripping methods, using mercury modified arrays to more recent advances in the field of biosensors (enzymatic, immunosensors and nucleic acid based ones).
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