Biocatalytic Membrane Electrodes Biosensors

Biocatalytic membrane electrodes have an ISE or a gas sensing electrode in contact with a thin layer of biocatalytic material, which can be an immobilized enzyme, bacterial particles or a tissue slice, as shown in Fig. 3 The biocatalyst converts substrate (the analyte) into product, which is measured by the electrode. Electrodes of this type are often referred to as biosensors . 

A representative example of a biocatalytic membrane electrode is an electrode for L-arginine The bacterium streptococcus faecium is immobilized on the gas permeable membrane of an ammonia electrode. Arginine deiminase in the bacterium catalyzes the following reaction 

Biocatalyst category Substrate Biocatalyst Detected substance Ref. 

Lactate 6-phospho-D-gluconate Lactate dehydrogenase ferri- 81) 

L-arginine and the excellent selectivity of the ammonia electrode for NH3. The working range of biosensors of this type is typically only two to three orders of magnitude with a detection limit of 10 to 10 M. 

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Biocatalytic membrane electrodes significantly expand the scope of direct potentiometry by enabling biosensors that respond to a whole host of organic substrates to be made. The selectivity of these sensors is a combination of the selectivity of the biocatalyst for the substrate and the ISE for other constituents in the sample that might reach the ISE surface membrane. Thus, the selectivity with respect to other organic constituents in the sample is determined by biocatalyst... 

L. Macholan, Biocatalytic Membrane Electrodes in Bioinstrumentation and Biosensors, L. D. Wise (ed), Marcel Dekker. New York, Basel, Hong Kong, 1991, Chap. 12. 

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