Microelectrochemical sensors

Finally, a median-based exclusion algorithm has been applied to data obtained with a fully implanted array of four microelectrochemical sensors.38,39 The Z-score was calculated from the values of individual sensors and the median absolute deviation, as shown in equation (8.11), and sensor readings were removed from the data set if the value was greater than one. 

New kinds of microelectrochemical sensors are described involving two redox active molecules immobilized onto a microelectrode. 

V. Tvarozek, I. Novotny, V. Rehacek, R. Ivanic and F. Mika, Thin-film electrode chips for microelectrochemical sensors. Nexus Res. News, 1 (1998) 15-17. 

Microfabrication and micromachining techniques have also been used in the manufacture of electrochemical sensors. This includes po and pco sensors. Zhou et al [9] describe an amperometric CO2 sensor using microfabricated microelectrodes. In this development, silicon-based microfabrication techniques are used, including photolithographic reduction, chemical etching, and thin-film metallization. In Zhou s study, the working electrodes are in the shape of a microdisk, 10 pm in diameter, and are connected in parallel. In recent years, silicon-based microfabrication techniques have been applied to the development of microelectrochemical sensors for blood gases, i.e. P02. Pcoj and pH measurements. 

Examples of successful impedimetric sensors (rather than conductivity or capacitance) are few. One example involved the fabrication of lignin-modified glassy carbon electrodes which are sensitive to ozone. Exposing the sensor electrodes to various ozone concentrations resulted in proportional changes in the charge-transfer resistance in the impedance spectmm. More recently, microelectrochemical sensors were prepared which are suitable for use in marine environments and were tailored to voltammetric and impedimetric or conductivity measurements. ... 

Realization of two-terminal microsensors like that represented in Scheme I depends on the discovery of viable reference and indicator molecules that can be confined to electrode surfaces. Described herein are three different microelectrochemical sensing systems. The first is a three-terminal microelectrochemical sensing system for CO based upon an indicator molecule, ferrocenyl ferraazetine, that selectively reacts with CO (2). The second microelectrochemical system is based upon a disulfide functionalized ferrocenyl ferraazetine that can be adsorbed onto Au or Pt via monolayer self-assembly techniques. Efforts to make a two-terminal CO sensor based upon the... 

Nagy et al. (1982) employed an ascorbate oxidase membrane to eliminate the oxidation current caused by ascorbic acid during the microelectrochemical mesurement of catecholamines in brain. The membrane was attached to a carbon microelectrode and was able to completely oxidize the penetrating ascorbic acid to electrochemically inert dehydroascorbic acid whereas the catecholamines could diffuse to the electrode. The sensor was called an eliminator electrode . 

Otagawa T, Madou M, Wing S, Rich-Alexander J, Kusanagi S, Fujioka T and Yasuda A 1990 Planar microelectrochemical carbon monoxide sensors Sensors Actuators B 1 319-25... 

Not long ago,this group first described microelectrochemical devices, which are based on microfabricated arrays of electrodes, connected by electroactive materials. Because the active components of these devices are chemical in nature, many of these devices are chemically sensitive,and comprise a potentially useful class of chemical sensors. Devices showing sensitivity to pH, 02r 2 f and Na" have been demonstrated. These devices are, typically, operated in fluid solution electrolytes. If this class of devices is to be useful as gas sensors, systems which are not dependent on liquid electrolytes need to be developed. We have recently reported solid state microelectrochemical transistors, which replace conventional liquid electrolytes with polymer electrolytes based on polyethyleneoxide (PEG) and polyvinylalcohol (PVA). In this report, we discuss additional progress toward solid-state devices by employing a new polymer ion conductor based on the polyphosphazene comb-polymer, MEEP (shown below). By taking advantage of polymer ion conductors we have developed microelectrochemical devices, where all of the components of the device are confined to a chip. 

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