Sensors reversible

Reversible sensors afford virtually symmetric transient signals (Fig. 2.18.A) on passage of the sample through the detector (e.g. see [15]). Such is the case with sensors involving a permanently immobilized... 

While reversible sensors are the ideal sensors, those irreversible sensors containing an immobilized reagent that can be regenerated approach the ideal... 

The two advantages of dosimeters derive from the fact that the final signal represents a record of total exposure over a given period. The dosimeter need not be continuously monitored, reducing power requirements substantially and a permanent record is available for documentation, important for such plications as health and safety monitoring. To obtain a comparable total-exposure record for reversible sensors requires maintaining a continuous record of response data for the entire time period of interest. 

For a reversible sensor, sensitivity is defined as the change in sensor output signal obtained for an incremental change in the concentration or mass of the analyte, i.e., the slope of the response-vs-concentration curve. Sensitivity for a reversible AW sensor typically has units of [frequency change]/[concentration change], e.g., Hz/M (M mol/L), Hz/(/ug/L), or even ppm >pm (normalized frequency shift/concentration). For an irreversible sensor, sensitivity is more appropriately defined in terms of frequency change/integrated exposure, e.g., Hz/M-min. 

For irreversible (non-equilibrium) sensors that utilize activated reaction ter-action mechanisms, sensitivity usually increases as a result of increased reaction rates at higher temperatures. This type of response behavior is illustrated in Ing-ure 5.5 for the reaction of a Pt-olefin-complex with ethyl acrylate [92d]. In contrast to the steady decrease in sensitivity for the reversible sensor, die SAW response rate (in Hz/min) increases with temperature. Thus, depending on the type of coating-analyte interactions being utilized, the sensor sensitivity can be improved by selecting an operating temperature consistent with the predominant response mechanism. 

Thus, immobilized HgCl2 could form the basis of a readily reversible sensor for aqueous chloride at moderate to high concentrations, though a tiny concentration of Cl would have to be present at all times in the contacting solution to prevent dissociation of the HgC complex. 

In contrast to the soluble probes described previously, sensors can be used to measure the concentration of glucose in body tissues or in flowing blood reversibly. Sensors are usually prepared via immobilization of the sensing components in polymer matrices. That is the approach we have taken. Our... 

We are especially interested in reversible sensors for volatile organic compounds (VOCs) in the atmosphere using conducting polymers as the sensing material. The most extensively us conducting polymer to date is polypyrrole (34-38) which is applied in certain commercial sensing instruments (39), Polyanil e, either in its protonated (doped) or non-doped forms, has been studied less extensively (40 45) and polythiophene to an even smaller extent (46-48),... 

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