Abstract
The rapid measurement of maltose is necessary in clinical and industrial food laboratories; maltose is a product of the reaction catalyzed by amylase, and is a component of food, such as commercial sugar, beer and milk. Enzyme sensors can accomplish this2, and several studies have been made in order to develop maltose sensors.3-' Two enzymes, one hydrolyzes maltose and the other oxidizes glucose, which is produced through hydrolysis, are usually used to construct maltose sensors.3-5 Although Ikeda et al.6'' reported on a monoenzyme electrode using oligosaccharide dehydrogenase, the electrode suffered from a rather low sensitivity for maltose. Kullick et al.3 have reported on the use of an a-glucosidase (a-GS)/glucose dehydrogenase (GDH) pair for preparing a maltose-sensing field-effect transistor. However, this sensor required the addition of NADH to the test solution, and showed low sensitivity (detection limit, 10-4 M)3; a-D-glucose is produced through the a-GS reaction (maltose+H2O-~2a-D-glucose), whereas GDH catalyzes the oxidation of /3-D-glucose, and the rate of isomerization from ato fl-form is slow. Another bi-enzyme sensor using a glucoamylase (GA)/glucose oxidase (GOD) pair equipped with an amperometric hydrogen peroxide-sensing electrode has been reported by Coulet and Bertrand4 and Varadi et al.5 Since GA catalyzes the hydrolyzation of maltose to produce a substrate of GOD, f3-D-glucose, the sensor can give a relatively large current response for maltose. However, such a GA/GOD-based electrode exhibits a current response to starch, which causes some difficulties when applying the electrode to the determination of amylase activity; starch is usually added to a test solution as a substrate for amylase. Alternative bi-enzyme systems that show high sensitivity for maltose and do not show any response to starch are therefore desired. Pyranose oxidase (PyOD) catalyzes the oxidation of both aand a-D-glucose. A combination of a-GS and PyOD is thus considered to be a suitable approach; a-GS does not hydrolyze starch. In this study we prepare a maltose sensor based on a layer containing a-GS and PyOD equipped with a hydrogen peroxide electrode; the results are compared with those of a GA/GOD-based electrode.
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