Cast films of lipid-coated enzymes as selective sensors for disaccharides

A stable enzyme film was prepared on a platinum electrode by casting organic solutions of a lipid-coated enzyme. The glucose oxidase (GOD)-immobilized electrode acted as a glucose sensor with a high sensitivity and a short response time. When the lipid-coated GOD was combined with a lipid-coated glycosidase on the electrode, the film showed a high selectivity for various disaccharides. For example, combining β -galactosidase with GOD, the electrode responded only to lactose (Gal β 1→4Glc), having β -galactoside at the non-reducing side of the disaccharide, but not to maltose (Glc α 1→4Glc) and cellobiose (Glc β 1→4Glc) in the aqueous solution. Similarly, an enzyme electrode sensitive only for maltose (Glc α 1→4Glc), cellobiose (Glc β 1→4Glc), and sucrose (Glc α 1→2Fru) could be prepared by using a mixed cast film of two lipid-coated enzymes, GOD and α -glucosidase, GOD and β -glucosidase, and GOD and invertase, respectively. This technique will become a new process not only for preparing sensor membranes but also for assembling water-soluble proteins on biological electrical components.