A Glucose Oxidase Electrode Based on Electropolymerized Conducting Polymer with Polyanion-Enzyme Conjugated Dopant
Won Jun Sung and You Han Bae*
Department of Materials Science and Engineering,Kwangju Institute of Science and Technology,1Oryong-dong, Puk-gu,Kwangju500-712,Korea
An enzyme immobilization method has been developed by electropolymerization chemistry of conducting polymer which results in a more effective and reproducible enzyme electrode.As a model system,in this study,glucose oxidase(GOD)was conjugated with a polyanion,poly(2-acrylamido-2-methylpropane sulfonic acid),via a poly-(ethylene oxide)spacer to improve the efficiency of enzyme immobilization into a conducting polymer.GOD was successfully conjugated with a high conjugation yield of more than90%,and its bioactivity was preserved.The resulting polyanion-GOD conjugate was used as a dopant for the electrochemical polymerization of pyrrole.Poly-pyrrole was effectively deposited on a Pt wire working electrode with the polyanion-GOD conjugate.The enzyme electrode responded to glucose concentrations of up to 20mM with a sensitivity of40nA/mM at an applied potential of0.4V within a response time of30s.Although the response signal decreased at the low applied potential of0.3V,the enzyme electrode showed sensitive response signals of about16nA/mM up to20mM in glucose concentration.Under the deoxygenated condition,re-duced but clear response current signal was obtained.The results show that the current signal response of the enzyme electrode to glucose concentration may be pro-duced by mixed mechanisms.
Since Clark and Lyons1developed the first enzyme-based oxygen electrode,biosensors have been studied and analyzed intensively.2-5Enzymes have been the most frequently used biomolecules,due to their superior selectivity and faster catalytic reaction rates.
There have been a variety of approaches taken in the develop-ment of enzyme-immobilization techniques.The physical entrap-ment of enzymes has been a common means of enzyme immo-bilization.In early enzyme-electrode models,an outer holding polymer membrane was used to prevent the enzyme from undergoing diffusional loss.6-9A more advanced method of physically entrapping enzymes was through matrixes made of synthetic10,11or natural gels.12,13In physical entrapment methods, due to the long electron-transfer pathway between enzymes and electrodes,electron mediators such as ferrocene derivatives14and osmium complexes15were often co-immobilized with the enzyme. Thus,a serious problem with such methods was the leakage of these harmful electron mediators when the enzyme electrode was used as an implantable biosensor.16Moreover,although these techniques are preferable for enzyme stability,they suffer from drawbacks such as complexity of the fabrication procedure and difficulties in miniaturization.
Other enzyme immobilization techniques have been investi-gated for more reliable enzyme attachment.Such methods include the covalent bonding of enzymes to a modified substrate by using a coupling agent such as carbodiimide17,18and the use of a covalent cross-linking agent such as glutaraldehyde.19,20These techniques offer the benefits of simplicity of fabrication and stable enzyme attachment.However,a covalent attachment may interfere with enzyme activity,and additional electron mediators are required due to the low sensitivity of the enzyme electrode.In fact, functionally reproducible,uniform coatings for active enzymes on an electrode have yet to be fabricated in miniaturizable size.
*Corresponding author:(Tel)+82-62-970-2361.(Fax)+82-62-970-2304. (E-mail)email@example.com
(20)Appleton,B.;Gibson,T.D.;Woodward,J.R.Sensors and Actuators,B1997,
10.1021/ac9908041CCC:$19.00?2000American Chemical Society Analytical Chemistry,Vol.72,No.9,May1,20002177 Published on Web04/04/2000