Composite enzyme-immobilised

Another possibility is to immobilise enzymes either on the sensor element itself or in the vicinity of the sensing element. The operation principle is in most cases a semi-continuous spectral difference measurement in combination with a kinetic data evaluation. A sample containing the analyte of interest is recorded by the sensor immediately after contact with the sample and again after a certain time. Provided that no other changes in the composition of the sample occur over time, the spectral differences between the two measurements are characteristic for the analyte (and the metabolic products of the enzymatic reaction) and can quantitatively evaluated. Provided that suitable enzymes are available that can be immobilised, this may be a viable option to build a sensor, in particular when the enzymatic reaction can not (easily) be monitored otherwise, e.g. by production or consumption of oxygen or a change of pH. In any case, the specific properties and stumbling blocks related to enzymatic systems must be observed (see chapter 16). 

The biocatalysts obtained were evaluated with respect to the composition, morphology, activity and stability of the immobilised enzyme in the starch hydrolysis reaction. In general, two alternative methods can be used, considering the bioartificial matrix as a substrate for the enzyme (this method is used for example to drive drug release into erosion control devices), or alternatively, as in the case of this work, after blending the enzyme with a polymer, and investigating its activity against an external substrate. The apparent kinetic parameters of the reaction catalyzed by the immobilised and native enzymes were determined and compared. 

Leheau T., Jouenne T. and Junter G.-A. Diffusion of sugars and alcohols throngh composite membrane structures immobilising viable yeast cells. Enzyme and Microbial Technology 22 (1998) 434-438. 

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