Biomedical Engineering Reference
In-Depth Information
(wall)
2e
-
Scheme 2.
Principle of the ferrocene-mediated thermal glucose biosensor,
D
q indicates the
heat produced in the reaction
poly(pyrrole)-coated reticulated vitreous carbon (RVC) matrix onto which tyro-
sinase was immobilized. The column functioned as enzyme reactor, working
electrode and thermally sensitive element together with the thermistors. Cate-
chol was oxidized by tyrosinase to form 1,2-benzoquinone, which was subse-
quently regenerated electrochemically on the electrode surface.The primary heat
production developed by the enzyme reaction could be measured calorimetri-
cally. Simultaneously, the electrochemical reduction of 1,2-benzoquinone gener-
ated a current that was detected by the working electrode. Such hybrid sensors
provide a useful tool for comparative studies of complex reaction schemes.
3.4
Other Applications
3.4.1
Enzyme-Activity Measurement
Significant interest has been generated in monitoring enzyme activity and
metabolite concentration in non-aqueous solvents [39, 40]. For example, the
reactions of immobilized lipoprotein lipase with tributyrin in a buffer-detergent
system and cyclohexane were compared using an ET. Also it was demonstrated
that horseradish peroxidase produced a considerably higher temperature signal
in toluene than in water. Furthermore, addition of diethyl ether in small
amounts was found to enhance this effect. In an analogous approach, the reac-
tion of chymotrypsin in 10% DMF for hydrolysis (exothermic) and synthesis
(endothermic) of peptide bonds was monitored using the ET.
3.4.2
Food
Several metabolites found in food samples have been estimated using the
thermometric approach. These include glucose, cellobiose, lactose, maltose,
galactose, lactate, oxalate, phopholipids, ascorbic acid, ethanol, urea [18],
xanthine and hypoxanthine [41, 42]. Glucose was estimated by co-immobilizing
glucose oxidase and catalase [43]. The presence of catalase doubled the thermal
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