CONDENSATION ALPHA-CYCLODEXTRIN POLYMER MEMBRANE WITH COVALENTLY IMMOBILIZED GLUCOSE-OXIDASE AND MOLECULARLY INCLUDED MEDIATOR FOR AMPEROMETRIC GLUCOSE BIOSENSOR

A highly permeable film of the condensation alpha-cyclodextrin polymer (alpha-CDP) was used as a membrane for fabricating a ''second-generat ion'' glucose amperometric biosensor. Glucose oxidase (GOD) was covale ntly immobilized, whereas 1,4-benzoquinone (BQ), or tetrathiafulvalene (TTF) mediator molecules were included in the membrane by the alpha-c yclodextrin sites. A simple one-step procedure for the biosensor prepa ration was developed. It consisted of casting the membrane onto the su rface of a glassy carbon, gold, or platinum disk substrate from an aqu eous solution, pH 2.0 (HCl), containing equimolar quantities of a wate r-soluble alpha-cyclodextrin prepolymer, a glutaric dialdehyde cross-l inking reactant, GOD, and the mediator. Cyclic voltammetry (CV) limiti ng currents for glucose biocatalytic electrooxidation were measured fo r different enzyme loadings and mediator dosings inside the membrane a s well as for different glucose concentrations in a (0.1 M phosphate b uffer + 0.1 M NaClO4) pH 7.0 solution. The limiting-electrocatalytic c urrents at the (alpha-CDP)-GOD-TTF electrode were pH independent and o ccurred at E(1/2) = 0.03 V (vs. SCE), i.e., at a favorably low potenti al value. The detectability of glucose was 10 mu M for the (alpha-CDP) -GOD-BQ electrode at the 2 mg (18.5 unit) GOD loading and a signal-to- noise ratio of 3. The values of apparent. Michaelis constant for gluco se and the maximum limiting electrocatalytic current density, determin ed from the Michaelis-Menten analysis for the 1 mg (18.5 unit) GOD loa ding, were (4.5 +/- 0.5) mM and (190 +/- 20) mu A cm(-2) for the (alph a-CDP)-GOD-BQ electrode, and (5.6 +/- 0.8) mM and (137 +/- 16) mu A cm (-2) for the (alpha-CDP)-GOD-TTF electrode, respectively. The sensor p erformance was examined with respect to the method of membrane prepara tion, membrane composition and long-term stability. Miniaturization of the biosensor is facile if, for instance, a 10 mu m Pt disk microelec trode substrate is used.