Micro-pH sensors

Some pH sensitive ionophores have been incorporated into liquid membranes in the construction of capillary glass micro pH sensors. Apart from ETH 1907 trido-decylamine [74], and ETH 2418 [4 -(dipropylamino)-2-azobenzene-carboxylic acid octadecylester] [75], the Fluka 95291 hydrogen ion sensitive resin cocktail A, a well-known commercial pH sensitive ionophore, has been used in many studies [76],... 

Some earlier developments and applications of various implantable pH sensors or measurement systems have been reported [128, 129, 130, 131]. However, reliable pH sensors for long-term implantations are still not available, and widespread clinical usage of implantable pH sensors has not been reached. Similar to other implantable sensors, the development of implantable pH microelectrodes, either fully implanted in the body or needle type sensors applied through the skin (percutaneous), has faced serious obstacles including sensor stability deterioration, corrosion, and adverse body reactions [48, 132, 133], Among them, encapsulation to prevent corrosion represents a major challenge for the implantable sensor devices [51]. Failure of encapsulation can cause corrosion damage on internal components, substrate materials, and electrical contacts [48], The dissolution of very thin pH sensitive layers will also limit the stability and lifetime of implantable micro pH sensors. 

Although much less so than pyrrole polymers, indole polymers are beginning to be synthesized and studied as new materials. Electropolymerized films of indole-5-carboxylic acid are well-suited for the fabrication of micro pH sensors and they have been used to measure ascorbate and NADH levels. The three novel pyrroloindoles shown have been electrochemically polymerized, and the polymeric pyrrolocarbazole has similar physical properties to polyaniline. 

Micro pH Sensors and Biosensors Based on Electrochemical Field Effect Transistors... 

Micro pH Sensors and Biosensors Based on Electrochemical Field Effect Transistors 139 Table 10.1 Coverage for each monolayer and molecular length of each moeity... 

P. N. Bartlett, J. Farrington, Electrochemically polymerized films of 5-carboxyindole possible application as a micro pH sensor, Bulletin of Electrochemistry 1992, 8, 208. 

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