Random microelectrode arrays

Individual electrodes in an array may assume a disordered (random) or periodical arrangement. Random microelectrode arrays are characterized by a statistical distribution of electrodes that may be of identical or dissimilar dimension and shape. Ordered microelectrode arrays generally consist of an ensanble of electrodes of identical dimensions with a periodic arrangement. 

Another way to characterize the electrochemical activity of miCToelectrode arrays is to map the electroactive species generated at each electrode by confocal Raman spectroscopy. Indeed, the use of confocal signal detection enables Raman spectroscopic measurements of very small sample volumes (even down to a few om ). Applied to a microelectrode array, it provides a statistical picture of the distribution of active sites on the array (60). As in the case of SECM, these two optical methods are particularly useful to verify if individual diffusion layers do not overlap and if the microelectrodes in the array are diffusely independent, particularly for random microelectrode arrays. 

A microelectrode array consists of a series of microelectrodes separated by an insulating material [36]. The microelectrodes can be regularly or randomly distributed (in the latter case the term ensemble is also used). Arrays containing hundreds or even thousands of microelectrodes wired in parallel have been... 

A more recent and very useful review [5] considers voltammetric/amperometric microelectrode arrays, their construction techniques, and various approaches to surface modification. This review includes disk and band microelectrodes with regular or random spacings between array elements. Several bioanalytical apphca-tions, including nucleic acid and protein detection, are included. 

Alternatively, an assembly of microelectrodes can alleviate some of the problems associated with the individual microelectrodes. Such a random array of microelectrodes (RAM) comprises about 1000 carbon fibres (each of diameter 5-7 pm) which are embedded randomly within an inert adhesive such as an epoxy resin. (The ends of the fibres need to be widely spaced.) The net result is to generate an electrode system with a superior response time and a current which is IfKK) times that of a single microelectrode. By increasing the current in this way, the sensitivity of measurement is further increased. 

Random array of microelectrodes (RAM) A microelectrode system comprising about 1000 carbon fibres embedded randomly within an inert adhesive such as an epoxy resin. 

If we approximate each of the inert blocking particles as being discshaped and of the same size, the modelling of a PBE is only very slightly different from modelling a random array of microelectrodes. In the latter case we considered an array of electroactive discs on an inert surface whereas for a PBE we consider an array of inert discs on an electroactive surface. The simple solution then is to use exactly the same simulation model as for the random array of microdiscs except that the surface boundary conditions... 

Instead of employing a single electrode, an array of electrodes [67] or an inter-digitated electrode [68] may be used to study electrochemical systems. Similar to advantages achieved by variations in electrode geometry, the use of several communicating electrodes poised at the same or different potentials opens up new possibilities for the study of the properties or the kinetics of chemical systems. An interesting development is the random assemblies of microelectrodes (RAM) (see Fig. II. 1.14), which promises the experimental timescale of microelectrodes but with considerably improved current-to-noise levels [69]. 

Figure 10.1 Classification of microelectrodes (A) random array, (B) ordered array, (C) paired electrode, schematic representation of a double band assembly, (D) interdigitated array, schematic presentation of IDA electrodes vertically arranged (E) linear array, (F) three-dimensional array, Utah electrode array (reprints from reference (28)). (for colour version see colour section at the end of the book).

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