Magnetic enzyme membranes as active elements of electrochemical sensors. Specific amino acid enzyme electrodes

Abstract

The basic principle of the described magnetic enzyme electrodes is a kinetic accumulation of CO2 at the active layer electrode interface. The local pCO2 level is linked to three simultaneous phenomena: substrate diffusion in, enzyme reaction CO2 diffusion out. After a transient state there is a stationary state between the quantity of CO2 produced by the enzyme reaction and the CO2 diffusing from the active membrane to the bulk solution. Continuous determination of free amino acids in biological media is useful in biological processing, fermentation, medicine, pharmaceutical industries and biological research. No methods are presently available for any specific continuous measurement of lysine which is of nutritional importance in protein industrial syntheses; of phenylalanine and tyrosine which have to be monitored in several inborn diseases (phenylketonuria being the most important of them); of arginine and histidine which play a still imperfectly understood part in neurochemistry. The use of decarboxylase bearing membranes as sensors in such measurements could offer several novel advantages: (a) a simple device made of a currently manufactured electrode slightly modified by the use of an enzyme membrane; (b) The absence of any enzymic consumption due to the immobilization and the negligible consumption of substrate during the measurements; (c) The sensitivity which can be sharpened by a systematic study of the membrane parameters; (d) the continuous response of the electrode as long as it is in contact with the substrate solution; (e) the further feasibility as a miniature sensor. The magnetic device introduced allows obviously a convenient use of the enzyme electrode, the active part can be removed and replaced without disturbance for the pCO2 electrode itself. The enzyme electrodes are not only useful at the applied point of view but also at the fundamental point of view by allowing a direct measurement of an intra membrane concentration. The influence of simple structures on enzyme kinetics was studied with enzyme electrodes by our group, in the case of memory and oscillations obtained with enzyme systems.