ENZYME BIOSENSOR

Advantages:

more specific than cell based sensors
faster responds due to shorter diffusion paths (no cell walls)

Disadvantages:

more expensive to produce due to the additional problem of isolating the enzyme
enzymes are often unstable when isolated
many enzymes need cofactors for the detection of substances

EXAMPLE OF AN ENZYME BIOSENSOR

The most widespread biosensor today is the glucose biosensor. It is very often used to measure the glucose concentration in blood. Its application for diabetis patients was also the driving force for the glucose sensor research.

There are quite a few enzymes which could be used as glucose detectors. Many of them require cofactors, though. The following example shows the glucose enzyme reaction with glucose oxidase. This enzyme doesn't require cofactors and is in addition one of the most stable enzymes for glucose detection:

Fig 7: Glucose assay with a biosensor

With the reaction shown above there are two possibilities to measure the glucose concentration: either one measures the oxygen consumption or the hydrogen-peroxide production. As a third option it would be also possible to measure the temperature increase due to heat released by the two reactions.
The presence of the second enzyme (catalase)a although not really essential for the assay, enhances the first reaction. This happens ue to the decomposition of the hydrogen-peroxide.

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