PH sensor solid state

Metal/metal oxides are the materials of choice for construction of all-solid-state pH microelectrodes. A further understanding of pH sensing mechanisms for metal/metal oxide electrodes will have a significant impact on sensor development. This will help in understanding which factors control Nemstian responses and how to reduce interference of the potentiometric detection of pH by redox reactions at the metal-metal oxide interface. While glass pH electrodes will remain as a gold standard for many applications, all-solid-state pH sensors, especially those that are metal/metal oxide-based microelectrodes, will continue to make potentiometric in-vivo pH determination an attractive analytical method in the future. 

H. Kaden, H. Jahn, and M. Berthold, Study of the glass/polypyrrole interface in an all-solid-state pH sensor. Solid State Ionics 169, 129-133 (2004). 

Miscellaneous. Iridium dioxide, like Ru02, is useful as an electrode material for dimensionally stable anodes (DSA) (189). Solid-state pH sensors employing Ir02 electrode material are considered promising for measuring pH of geochemical fluids in nuclear waste repository sites (190). Thin films (qv) of Ir02 are stable electrochromic materials (191). 

P. H. Huang and K. G. Kreider, Electrvchem. Eval. Solid State pH Sensors Nuclear Waste Contain. 89, 30 (1989). 

The acid-base properties of polyaniline can be utilized to produce solid-state pH sensors where polyaniline works both as the pH-sensitive material and as the ion-to-electron transducer. An excellent example is the electrodeposition of polyaniline on an ion-beam etched carbon fiber with a tip diameter of ca. 100-500 nm resulting in a solid-state pH nanoelectrode with a linear response (slope ca. — 60mV/pH unit) in the pH range of 2.0-12.5 and a working lifetime of 3 weeks [104]. The response time vary from ca. 10 s (around pH 7) to ca. 2 min (at pH 12.5). 

Figure 15.8 A commercial microelectrode for pH measurements in volumes as small as 10 p,L. The electrode has a solid-state pH sensor and a flexible pol3fpropylene stem, making it extremely rugged and suitable for use in the field. This electrode can be used to determine pH in single droplets of water on leaves of plants or blades of grass to study acid rain deposition. [Courtesy of Lazar Research Laboratories, Inc., Los Angeles, CA (www.lazarlab.com).]...

CNTs are also widely used in actuators [168-171], The addition of CNTs to PANI fibers increased the electromechanical actuation because the CNTs improved the mechanical, electronic and electrochemical properties of the PANI fibers [172-174], Composites based on CNTs are studied for a variety of sensor applications [175-177], For example, polypyrrole or PANI deposited on single-walled CNT networks that can be used as solid state pH sensors [178], A DNA sensor was created fi om a composite of polypyrrole and CNTs fimctionalized with carboxylic groups to covalently immobilize DNA onto CNTs [179], In general, the presence of CNTs tends to increase the overall and selectivity of biosensors, The thermal transport properties of polymer composites can be improved with the addition of CNTs due to the excellent thermal conductivity of CNTs, Such composite are quite attractive for usages as printed circuit boards, connectors, thermal interface materials, heat sinks, lids, housings, etc, [92,180],... 

Composite films of CNTs with other materials, such as conducting polymers or ceramics, are very fascinating materials for the development of electrochemical sensors. Yang and co-workers fabricated an electrode via electropolymerization of acid chrome blue K at an MWNT-functionalized glassy carbon electrode for simultaneous determination of dihydrox-ybenzene isomers in real water samples through applying the first-order linear sweep derivative voltammetry. Polypyrrole (PPy) or polyaniline (PANI) was electrochemically deposited on SWNT networks by Ferrer-Anglada and co-workers ° in 2006, which has been used as solid-state pH sensors. 

W. Vonau, J. Gabel, and H. Jahn, Potentiometric all solid-state pH glass sensors. Electrochim. Acta 50, 4981-4987 (2005). 

Solid-state cadmium sensors based on chalcogenide thin film layer were prepared [388]. The electrochemical behavior of the sensor in terms of ionic sensitivity, detection Emit, Nernstian response interval and effect of pH was evaluated. 

Solid-state chemical sensors are fabricated by the same technology used for microelectronic chips. The field effect transistor (FET) is the heart of commercially available sensors such as the pH electrode in Figure 15-24. 

Solid-state ion sensors with conducting polymers as sensing membranes have also proved useful in some applications. Of particular importance are the pH sensors based on polyaniline that can be also applied in non-aqueous solutions. Polypyrrole-based sensors for nitrate also show great promise for water analysis. However, in addition to these two excellent examples, a large number of functionalized conducting polymers have been synthesized already, and these materials may offer unique possibilities for fabrication of durable, miniaturized ion sensors. 

Dissolved oxygen sensors, pH electrodes, or specific ion electrodes can be fitted, and a fluorometer for petroleum oils was developed from the chlorophyll sensor (sensitivity, 1 /xg of naphthalene/L). A solid-state bioluminescence sensor was developed (18) with a minimum detection of 5 x 10 W equivalent to about 10 quanta/s at 480 nm, sufficiently low for the detection of a single dinoflagellate flash (19). 

In recent years further concepts have been developed for the construction of polymer-based diodes, requiring either two conjugated polymers (PA and poly(A-methyl-pyrrole) 2 > or poly(A-methylpyrrole in a p-type silicon wafer solid-state field-effect transistor By modifying the transistor switching, these electronic devices can also be employed as pH-sensitive chemical sensors or as hydrogen or oxygen sensors 221) in aqueous solutions. Recently a PPy alcohol sensor has also been reported 222). 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

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