Glucose sensors enzyme-based systems

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

The response of the sensor peaked within 4 min and the calibration curve is applicable within the range of glucose concentrations in normal human serum. Another glucose sensor using sol-gel systems was based upon glucose oxidase in conjunction with a mediator compound (ferrocene or hexacyanoferrate) that transferred an electron to the enzyme [211], This system can be represented as... 

Researchers turned their attention to applications of silica gel as a new electrode material. Silica gel, which has a three-dimensional structure with high specific surface area and is electroinactive in an aqueous medimn can be used as a support for electroactive species during their formation and/or enzymes by adsorption or entrapment [92,93]. Patel et al. recently reported application of poljwinyl ferrocene immobilized on silica gel particles to construct glucose sensors. Efficiency of carbon paste electrodes prepared with these polymeric electron mediators and GOx was comparable to electrodes constructed with other ferrocene based polymeric electron transfer systems. The fact that 70% of initial anodic current was retained after a month when electrodes were kept in the buffer at room temperature shows that polymerization of monomer vinylferrocene in the pores of silica gel and entrapping GOx in the matrix of poljwinyl ferrocene appears to have added stability to the sensors [94]. 

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