| Abstract
| - The catalytic reaction of glucose oxidase (GOx) mediatedby 3-(10-phenothiazyl)propionic acid (PT-PA) and phenothiazine-labeled poly(ethylene oxide) (PT-PEO1000)that are covalently bonded to Au(111) electrodes has beeninvestigated. The PT-PA and PT-PEO1000 are reactedwith 2-aminoethanethiol (AET), followed by the formationof a self-assembled monolayer (SAM) onto the Au surface.The PT group immobilized on the SAM of AET acts as aneffective mediator for the electron transfer (ET) betweenthe electrode and the FAD center of freely diffusing GOxin solution. The ET rate constant estimated from thecatalytic current using a newly derived equation is largerby 1 order of magnitude for the PT-PA-modified system(1.1 × 105 dm3 mol-1 s-1) than for the PT-PEO1000system (1.4 × 104 dm3 mol-1 s-1). The order of themagnitude of the ET rate constant clearly contrasts withthe GOx hybrid systems that we previously investigated(Anal. Chem. 2003, 75, 910−917), in which the presence of the PEO spacer enhances the ET reaction rate.The reduction in the apparent PT concentration at theelectrode interface due to the high mobility of the PEOchain, leading to low efficiency in the formation of anenzyme-mediator complex, is a possible reason for thelower mediation ability of PT-PEO1000 than that of PT-PA for the ET between the FAD group and PT+ immobilized on the electrode. Inhibition of the penetrationof GOx molecules into the monolayer and of the accessibility of some part of PT groups to GOx molecules couldalso be reasons for the lower mediation ability of PT-PEO1000 thickly modified on the electrode.
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