Development of sensitive and selective glucose colorimetric assay using glucose oxidase immobilized on magnetite-gold-folate nanoparticles

We constructed a new nanocomposite catalyst that demonstrated enzyme mimetic activity, like peroxidase, for the colorimetric detection of glucose, using glucose oxidase (GOx) immobilized by glutaraldehyde cross-linking on a gold-coated magnetite nanoparticle (Fe3O4@Au) core, encased within a conjugated cysteine (Cys) folic acid (FA) shell. The synthesized Fe3O4@Au-Cys-FA NPs were characterized using AFM, XRD, DLS and FT-IR analysis. The as-prepared Fe3O4@Au-Cys-FA-GOx nanocomposites were used to catalyze the oxidation of glucose to generate H2O2, coupled with catalyzing the oxidation of a peroxidase substrate, 2,2'-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)-diammonium salt (ABTS), to ABTS(center dot+), thereby enabling the colorimetric detection of a colored oxidization product. The proposed nanocomposite exhibits good biocompatibility and provides highly efficient immobilization and retention of GOx. The designed colorimetric method provides a linear dynamic range for glucose detection from 10 mu M to 1 mM (r(2) = 0.998) and a detection limit of 3.8 mu M (3 S.D. blank/slope) with a good reproducibility and the nanocomposite is reusable (>= 6 times). Moreover, an interference study revealed that maltose, fructose and sucrose do not affect the colorimetric measurement. The developed method was successfully applied for glucose determination in energy and sports drinks. It is also expected that an expansion of the designed colorimetric method beyond this application may be possible in the future.