Disk-in-glass microelectrodes

This tip preparation technique is one of the rare benchtop methods allowing nanometer-sized microelectrodes having a disk-in-glass geometry to be reproducibly fabricated. These nanoelectrodes could be used as sensitive SECM probes provided the very large glass sheath surrounding the microelectrode disk can be thinned down in some way to yield acceptable RG values. 

To prepare surface-modified colloidal membranes, a thin colloidal film was assembled from440 11 nm and 184 9 nm silica spheres [26,28] on the surface of 25 pm radius, disk-shaped Pt microelectrodes shrouded in glass [26], These electrodes were... 

Planar NO microsensors are constructed similarly to the planar metal disk microelectrodes commonly used in scanning electrochonical microscopy (SECM, see Chapter 12). The working electrodes are prepared as follows (i) The metal (e.g., Pt) disk electrode is encased in glass and the surrounding glass sheath reduced as described in Section 6.3.1 and in reference (19). The bare metal electrode is then chonicaUy modified to enhance the kinetics for electrochemical oxidation of NO on its surface. 

Fig. 14 SECM images showing oxygen reduction on a smooth Pt disk microelectrode (127 gm diameter) embedded in glass, recorded in the TG-SG mode of SECM Scan rate = 300 (im s , sample potential (Ej) = 0.1Vad = 30 pm ix = 76 nA. bd = 5 pm ix = 36 nA. In both (a) and (b), the lower figure is a false eolor image where the eurrent is represented by the color, and the upper is an aetual representation of steady-state current i as a function of the x-y position...

In most cases, Do is about 10 cm s, and it then follows that the characteristic radius of an UME is smaller than 6 [im. However, it is important to notice that Do is sometimes appreciably smaller than 10 cm s if O is a very large molecule, or, more likely, if a viscous or glass-like medium is used planar diffusion would then prevail even at a radius of 6 pm. Note also that a microelectrode with a radius of 100 pm experiences a substantial contribution from spherical diffusion. If the geometry of the electrode differs from the simple disk or microsphere shape, the definition is less clear. In general, the characteristic behavior of a UME is observed if at least one of the dimensions is in the micrometer range. For instance, a band electrode with a width of less than 10 pm behaves as an UME even if it is several mm long. 

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