REMOVING THE INFLUENCE OF BUFFER CONCENTRATION ON THE RESPONSE OF ENZYME FIELD-EFFECT TRANSISTORS BY USING ADDITIONAL MEMBRANES

Urea- and glucose-sensitive enzyme field effect transistors (ENFETs) were prepared by cross-linking urease and glucose oxidase, respectively, with bovine serum albumin (BSA) in saturated glutaraldehyde vapour on the gate area of the ISFETs. Additional BSA and polyvinylbutyral membranes were formed by a dip-coating procedure from the appropriate solutions on the top of the enzyme layer. In case of the urea ENFET the additional albumin membrane led to complete elimination of the influence of the buffer concentration on the sensor response. For the glucose ENFET additional BSA membranes resulted in an extension of the dynamic range of the sensor up to a glucose concentration of 25 mM while not affecting substantially the buffer effect on the sensor response. However, after the formation of one more additional polyvinylbutyral membrane more than a fivefold decrease in the influence of the buffer concentration on the biosensor response was observed.