Oxidase-functionalized Fe3O4 nanoparticles for fluorescence sensing of specific substrate

This study reports the development of a reusable, single-step system for the detection of specific substrates using oxidase-functionalized Fe3O4 nanoparticles (NPs) as a bienzyme system and using amplex ultrared (AU) as a fluorogenic substrate. In the presence of H2O2, the reaction pH between Fe3O4 NPs and AU was similar to the reaction of oxidase and the substrate. The catalytic activity of Fe3O4 NPs with AU was nearly unchanged following modification with poly(diallyldimethylammonium chloride) (PDDA). Based on these features, we prepared a composite of PDDA-modified Fe3O4 NPs and oxidase for the quantification of specific substrates through the H2O2-mediated oxidation of AU. By monitoring fluorescence intensity at 587 nm of oxidized AU, the minimum detectable concentrations of glucose, galactose, and choline were found to be 3, 2, and 20 μM using glucose oxidase–Fe3O4, galactose oxidase–Fe3O4, and choline oxidase–Fe3O4 composites, respectively. The identification of glucose in blood was selected as the model to validate the applicability of this proposed method.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The GOx–Fe3O4 composites provided a one-step assay for the fluorescence detection of glucose. ► GOx immobilized on the surface of the GOx–Fe3O4 composites is reusable for the detection of glucose. ► The GOx–Fe3O4 composites can be applied to detect glucose in a complex biological sample. ► Compared to peroxidase-like Fe3O4 NPs, a system of GOx–Fe3O4 composite and AU provided better sensitivity toward glucose.