Potentiometric tips, scanning electrochemical microscopy

Scanning electrochemical microscopy can also be applied to study localized biological activity, as desired, for example, for in-situ characterization of biosensors (59,60). In this mode, the tip is used to probe the biological generation or consumption of electroactive species, for example, the product of an enzymatic surface reaction. The utility of potentiometric (pH-selective) tips has also been... 

In scanning electrochemical microscopy (SECM) a microelectrode probe (tip) is used to examine solid-liquid and liquid-liquid interfaces. SECM can provide information about the chemical nature, reactivity, and topography of phase boundaries. The earlier SECM experiments employed microdisk metal electrodes as amperometric probes [29]. This limited the applicability of the SECM to studies of processes involving electroactive (i.e., either oxidizable or reducible) species. One can apply SECM to studies of processes involving electroinactive species by using potentiometric tips [36]. However, potentio-metric tips are suitable only for collection mode measurements, whereas the amperometric feedback mode has been used for most quantitative SECM applications. 

Most scanning electrochemical microscopy (SECM) experiments are conducted in the amperometric mode, yet microelectrodes have for many years been used as potentiometric devices. Not surprisingly, several SECM articles have described how the tip operated in the potentiometric mode. In this chapter we aim to present the background necessary to understand the differences between amperometric and potentiometric SECM applications. Since many aspects of SECM are covered elsewhere in this monograph, we have focused on the progress made in the held of potentiometric microelectrodes and presented it in the context of SECM experiments. Starting with an historical perspective, the key discoveries that facilitated the development and applications of micro potentiometric probes are highlighted. Fabrication techniques and recipes are reviewed. Basic theoretical principles are covered as well as properties and technical operational details. In the second half of the chapter, SECM potentiometric applications are discussed. There the differences between the conventional amperometric mode are developed and emphasized. 

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