Flow-through calorimetric biosensors

Any (bio)chemical reaction is accompanied by energy conversion, most often in the form of heat production, the amount of heat produced being proportional to that of substance converted. Therefore, heat is a highly nonspecific expression of a (bio)chemical reaction but can be used as indicative for a given substance when this is selectively converted (e.g. by effect of a catalyst, particularly an enzyme). This section discusses three types of sensors based on the use of as many types of devices for measurement of the heat involved in a biochemical reaction, namely fibre optics, polymer films and thermistors. 

These films have a thin metal coating that is vapour-deposited on each surface to facilitate the electrical polling process and can be used to make electrical contact in sensor applications. 

Thermistor basedflow-through calorimetric sensors. Enzyme thermistors make the most widely developed type of heat measurement-based sensors. The thermistors are normally used as temperature transducers in these devices. Thermistors are resistors with a very high negative temperature coefficient of resistance. They are ceramic semiconductors made by sintering mixtures of metal (manganese, nickel, cobalt, copper, iron) oxides. Like the two previous groups, thermistor sensors do not comply strictly with the definition of sensor as they do not consist of transducers surrounded by an immobilized enzyme rather, they use a thermistor at the end of a small 

Even though most enzyme thermistors have been used for determining substrates, a few applications to the determination of inhibitors and activators, as well as enzyme activities, have also been reported. The enzymes employed for this purpose are usually isolated previously, though some are used in their original tissues and microorganisms [157]. 

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