Band microelectrode current

Background current, 21, 65 Background subtraction, 40, 106 Bacteria electrode, 182 Band microelectrodes, 130, 135 Beryllium, 82 Bienzyme electrodes, 175 Biocatalytic devices, 172 Biological recognition, 171 Biosensors, 50, 171 Bipotentiostat, 106 Blood electrolyte, 165 Boltzmann equation, 19 Brain analysis, 40, 116 Butler-Volmer equation, 14... 

The forward and reverse currents i/rf and i//( of the square wave voltammograms corresponding to Fig. 7.5c are shown in Fig. 7.6a for microelectrodes of the four electrode geometries considered. From these curves, it can be seen that both currents present a sigmoidal shape and they are separated by 2Esw in the case of spheres and discs. This behavior clearly shows that the steady state has been attained. On the other hand, in the case of cylinders and bands, y/f and i/// show a transient behavior under these conditions. From Fig. 7.6b, c, it can be verified that a decrease in the radius, ((w/2) = rc = 0.1 pm) and that of both radius and frequency (Fig. 7.6c, (w/2) = rc = 0.1 pm and/= 10 Hz) do not lead to a stationary SWV response at cylinder and band microelectrodes. 

Szabo A, Cope DK, TaUman DE, Kovach PM, Wightman RM (1987) Chronoamperometric current at hemicylinder and band microelectrodes theory and experiment. J Electroanal Chem 217 417 23... 

Szabo, A. Cope, D. Tallman, D. Kovach, D. Wightman, P. Chronoamperometric current at hemicylin-der and band microelectrodes—Theory and experiment. J. Electroanal. Chem. 1987, 217,417-423. 

Microelectrodes were mentioned previously in Chapter 5, where we saw how their small size increased the faradaic efficiency since the interfacial capacitance Cdi is decreased, itself minimizing the charging currents. Microelectrodes can be purchased relatively cheaply, and in a variety of types, e.g. hemispherical and flat circular rings or bands, with a wide range of diameters. Such electrodes were discussed previously in Section 5.3. 

In addition to disks and cylinders, microelectrodes with the geometry of bands and rings have also been constructed and used. Bands, like cylinders, exhibit the properties of microelectrodes by virtue of their narrow width, yet pass large currents due to their length. Ring electrodes, on the other hand, have been of interest because they can be constructed with very small surface areas. 

The effect of the electrode geometry and size is shown in Fig. 6.16, where the curves are plotted for co = 5 and different values of the characteristic dimensions of microelectrodes of different geometries (rs, rd, and w/2 for spheres, discs, and bands respectively with rs = rd = w/2). For large electrodes (Fig. 6.16a), the curves (i.e., the current density) show small differences because diffusion is almost planar and... 

The UMDE evinces strong edge effects or very uneven current densities along the radius of the disk. It shares this problem with all the other flat microelectrodes such as microbands or rings. The exception of course are the hemispherical or hemicylindrical microelectrodes, which have no effective edges and behave as half of a sphere or cylinder, and also deeply recessed disks or bands, which approach the shrouded types. 

BAND MICRQELECTRODE. These electrodes have an active surface with one dimension in the micrometer range and the other several millimetres long. They retain many of the features of the microelectrodes but have two additional advantages they have a much higher current due to their large surface area and it is relatively easy to have two (or more) closely spaced. When the distance between the electrodes is in the micrometer range each electrode is within the diffusion layer of the other, and the reactions ta)dng place at one influence the activity of the other and vice versa (16). 

Cope DK, Scott CH, Kalapathy U, TaUman DE (1990) Transient behavior at pltmtir microelectrodes. Diffusion current at a band electrode by an integral equation method. Part... 

Cope DK, Tallman DE (1990) Transient behavior at planar microelectrodes. A comparison of diffusion current at ring, band and disk electrodes. J Electroanal Chem 285 85-92... 

Where m is number of microband electrode pairs, b is the band length and Wb and Wg are the microband and the gap width, respectively. From this equation, it is evident that the smaller the gap between the microelectrodes, the higher the redox cycle number obtained and, as a consequence, the higher the current enhancement. Narrow-gap 1AM offers high sensitivity and short response time. The 1AM electrode also has a small sample volume requirement for practical measurements. These characteristics make LAM suitable for the detection of biological substances and for detection in liquid chromatography (LC) or flow injecticMi analysis (FIA). 

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