Effect of the modification of phenothiazine-labeled poly(ethylene oxide) on the solubility and enzymatic electrocatalytic reaction of glucose oxidase in water/1-butyl-3-methylimidazolium tetrafluoroborate mixtures

In water/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) mixtures, the solubility and electrocatalytic properties are compared between native glucose oxidase (GOx) mixed with phenothiazine-labeled poly(ethylene oxide) (PT-PEO) mediator and GOx-(PT-PEO) hybrid, in which PT-PEO is covalently attached to the surface lysine residues, under a substrate-saturated and diffusion-limited condition. The electrocatalytic current (Icat) of native GOx mixed with PT-PEO is observed only in the mixtures with low IL content (∼30 wt%) wherein GOx is soluble and decreases with increasing the content of IL. The decrease in Icat is not fully attributable to the reduction in the diffusion rate of mediators due to the increase in the viscosity of the mixtures, suggesting the deterioration of the electron transfer (ET) reaction from FADH2/FADH to PT+-PEO (ket). The modification with PT-PEO not only increases the solubility of GOx but also enhances the ket. The ket value of the hybrids is less influenced by the IL addition than that of the mixed systems, resulting in the smaller dependence of Icat on the IL content and the Icat value larger than that of the corresponding mixed system with the same ratio of [PT-PEO]/[GOx].