An alpha-Amylase Biosensor with 1,1-Dimethyl-3-(2-Amino-1-Hydroxyethyl) Ferrocene as an Electron Transfer Mediator

A new disposable α-amylase biosensor has been developed based on the encapsulation of both the glucose oxidase (GOD) and the α-glucosidase in the composite film of the sol-gel/Nafion.1, 1-dimethyl-3-(2-amino-1-hydroxyethyl) ferrocene (DMAHFc) as an electron transferring mediator was immobilized on the screen-printed electrode surface by Nafion. Under optimal conditions this biosensor was able to detect α-amylase activity in the linear range of 15-980 IU L^-1 (R² = 0.9523), which was wider than some of other α-amylase biosensors using the flow-injection-type assay and some of other biosensors using the gelatin membrane. Three components DMAHFc, sol-gel and Nafion not only enhanced the electron transfer, but also improved the sensitivity and long-term stability of the biosensor. The limit of detection of 1.2 IU L^-1 was obtained, in comparison to detection limits of 50 IU L^-1 obtained by some of other α-amylase biosensors using the flow-injection-type assay and 17 IU L^-1 obtained by some of other biosensors using the gelatin membrane. The activity of salivary α-amylase can be detected by the biosensor with a fast response, high sensitivity, good reproducibility, and long-term stability. So, it is possible to construct a new method to identifies people's mental stress conditions conveniently.