Glucose sensing based on an effective conversion of O₂ and H₂O₂ into superoxide anion radical with clay minerals

An effective promotion for the generation of superoxide anion radical from H₂O₂ and O₂ was accomplished with montmorillonite K10 clay mineral (denoted Mont. K10). This catalytic event was characterized by a fluorescence assay using amplex red and superoxide dismutase (SOD) as probes. The iron species (Fe^II and Fe^III) contained in Mont. K10 are thought to contribute to this catalytic event. Due to this property, a glucose sensor was fabricated on the basis of Mont. K10, amplex red, and glucose oxidase (GO_x). When glucose is injected with amplex red over the clay|GO_x electrode, H₂O₂ is produced in the enzyme zone, transduced to superoxide anion radical by the clay, and quenched by amplex red. Since the resulting product, resorufin, is emission-active under the irradiation of visible light (λ_ex: 563 nm; λ_em: 583 nm, pH 8), the analyte can thus be recognized and reported as optical signals with a luminescence spectrometer via a Y-type optical fiber atop of the electrode. The optical signal showed a linear response to glucose up to 150 μM at pH 8. The lower and upper limits were estimated to be 1.0 and 150 μM, respectively, at this pH. These results suggest that Mont. K10 is a promising O2- transducer.