Integration of sorption, reaction and detection

Most of these sensors fit the general configuration shown in Fig. 5.1.C, i.e. the simultaneous sorption, reaction and detection involved cannot be resolved in space or time. However, separation occasionally takes place in the same zone, but sequentially, before (type A) or after (type B) the (bio)chemical reaction, whereas detection is simultaneous with the reaction or separation, respectively. 

The sorbent materials used to construct this type of sensor are widely varied (ion exchangers, adsorbent solids, polymers) and are employed as particles (larger than 30 pm in order to avoid overpressure in the flow system) or films. Most of these sensors are optical and rely on absorption, reflectance or molecular fluorescence measurements. In order to ensure that the sensing microzone is fully compatible with the detector, the sorbent material used must be as transparent as possible (photometry) or give rise to no appreciable light scatter (fluorimetry) so that the baseline (resulting from passage of the carrier) may be as low as possible. 

The descriptions of sensors integrating sorption, reaction and detection provided below are classified according to the type of immobilization 

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