Enzyme monolayer-functionalized field-effect transistors for biosensor applications

A gate surface of an ion-selective field-effect transistor was modified wit h a monolayer enzyme array that stimulates biocatalytic reactions that cont rol. the gate potential. Stepwise assemblage of the biocatalytic layer incl uded primary silanization of the Al2O3-gate with 3-aminopropyltriethoxysila ne, subsequent activation of the amino groups with glutaric dialdehyde and the covalent attachment of the enzyme to the functionalized gate surface. U rease, glucose oxidase, acetylcholine esterase and alpha -chymotrypsin were used to organize the biocatalytic matrices onto the chip gate. The resulti ng enzyme-based field-effect transistors, ENFETs, demonstrated capability t o sense urea, glucose, acetylcholine and N-acetyl-L-tyrosine ethyl ester, r espectively. The mechanism of the biosensing involves the alteration of the pH in the sensing layer by the biocatalytic reactions and the detection of the pH change by the ENFET. The major advantage of the enzyme-thin-layered FET devices as biosensors is the fast response-time (several tens of secon ds) of these bioelectronic devices. This advantage over traditional thick-p olymer-based ENFETs results from the low diffusion barrier for the substrat e penetration to the biocatalytic active sites and minute isolation of the pH-sensitive gate surface from the bulk solution. (C) 2000 Elsevier Science B.V. All rights reserved.