Other Sensor Technologies

Apart from the aforementioned most frequently used sensor technologies, also selective electrochemical sensor combinations have been commercialised for use in dedicated applications. The combination of electrochemical CO, H2S, SO2 and NH3 sensors was used for quality and freshness control of foods like fish [98] and meat [99]. Combinations of MOSs and MOSFETs supplemented with a selective IR absorption sensor for carbon dioxide and a humidity sensor for measuring relative humidity were also described [100]. 

Advances in the production, immobilisation and characterisation of mammalian olfactory receptors led to the development of biosensors where isolated olfactory binding proteins were deposited on the surface of QMBs [102, 103] or were connected to nanoelectrodes [104]. Although still at the development stage, such an array-type device coated with different olfactory receptors will be a powerful and useful tool for detecting and discriminating odorants in the future. 

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Other medical products based on optical sensor technology include those of Cardiomed (System 4000), Puritan-Bennett, and one of Radiometer (Copenhagen) which has been withdrawn meanwhile. Optical (but non-fiber) sensors for oxygen and for C02 also are widely used for the determination of bacteria in blood. In 1986, Gehrich et al.36 described an optical fluorescence... 

Sensing schemes have become reliable enough to be of practical utility, instrumentation has become available at costs that make this sensor technology competitive to established sensors, and numerous other sensors schemes have been presented that are of interest, at least from an academic point of view. 

Among the great variety of organic chromophores such as azo dyes, nitrophenols, phthaleins, sulfophthaleins, aniline-sulfophthaleins, triphenylmethane dyes, polymethines, and others, only a few have so far been considered to be useful and applied to sensor technology (Table l)25 34. Important characterization parameter of pH indicator is its pKa value ... 

For third-party damage, other sensors such as acoustic (hydrophone)-based technology is also being developed (Figure 10.20). 

This concept is in essence a chromatographic effect similar to that observed in gas chromatography (GC), with the conjugated polymer film acting as the stationary phase. It is possible that like in GC and other candidate technologies for explosive detection, these responses could be empirically standardized for expected analytes of interest and sensory devices caHbrated to deconvolute temporal quenching signals to determine which analytes are present. This would further enhance the selectivity of what is already a very selective sensor for TNT and related compounds. 

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