Construction of thermal enzyme sensors

Commercial glucose oxidase often contains catalase and the following reactions may occur  

The total variation in enthalpy, AH3 = AH) + AH2 43 kcal, is the value detected by the thermal transducer. 

The following reaction can be catalysed by immobilized urease on a thermal transducer 

This reaction produces a low variation in enthalpy and so a glass sheath must be positioned around the thermistor to limit thermal diffusion. This device improves the sensitivity and the detection limit of the biosensor. The same pH effect is found for this sensor (Rgure 4.38) as was found for other enzyme sensors, but the response time is much shorter (less than 10 seconds). 

Enzymatic thermistors also require control for any disturbance of the sample medium. The substrate of the enzymatic reaction must be added as regularly as possible to avoid high levels of thermal noise. The use of a laminar flow cell [220] can improve the detection limit for urea (10 M), but also reduces the sensitivity of the sensor. 

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