Enzyme Membrane Sensors for Glucose

The development of enzyme membrane sensors for glucose began with the first enzyme electrode constructed by Clark. The sensors developed since differ with respect to the biological component and, even more, with the transducer type used. A common element to all of them is that the biocomponent is fixed in front of the transducer by a semi-permeable membrane. 

Several authors investigated ion selective electrodes incorporating GOD coupled with oxidative reactions catalyzed by horseradish peroxidase (HRP). Thus, glucose has been determined by measuring iodide concentration at an iodide sensitive electrode (Nagy at al., 1973) according to  

The enzymes have been both physically entrapped in polyacrylamide on nylon netting and chemically bound to polyacrylic acid derivatives both preparations exhibited large measuring times. Improvement of the system in favour of the response time diminished the sensitivity of the sensor. The authors reported a response time between 77 and 235 s and a sensitivity of 40 mV per concentration decade. Besides the low selectivity of the iodide sensitive electrode (thiocyanate, sulfide, cyanide, and silver(I) ions interfere), disturbances by other HRP substrates, e.g. uric acid, ascorbic acid, and Fe(II) ions, restrict the applicability of the method. 

Al-Hitti et al. (1984) compared the GOD-HRP sequence with a system in which HRP has been replaced by ammonium molybdate  

The enzymes are immobilized in poly(vinyl chloride) as follows 50 mg GOD (6500 U) and 18 mg HRP (6000 U) are mixed with 20 mg PVC and 6 ml tetrahydrofuran 40 mg dioctylphenyl phosphate are added as 

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