Application of magnetic core–shell microspheres on reagentless immunosensor based on direct electrochemistry of glucose oxidase for detection of carbohydrate antigen 19-9

This paper reported the production of magnetic core–shell composite microspheres (Fe3O4@SiO2–Au@mSiO2) which consist of a silica-protected magnetite particle core, an active gold nanoparticle transition layer and an outer mesoporous silica shell with pore channels. During the synthesis of the microspheres, the shape of the nanocomposite was changed from hexagons or quadrangles of Fe3O4 to well-defined spheres of Fe3O4@SiO2–Au@mSiO2. The synthesized microspheres were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. A strategy was proposed for the fabrication of reagentless immunosensors based on direct electrochemistry of glucose oxidase (GOD), which employed multiwall carbon nanotubes and the prepared Fe3O4@SiO2–Au@mSiO2 as immobilization matrix. The immobilized GOD exhibited direct electrochemistry with a rate constant of 1.8 s−1. The cyclic voltammetric (CV) and differential pulse voltammetric (DPV) peak currents of GOD decreased linearly with the increase of carbohydrate antigen 19-9 (CA19-9) concentrations from 0.01 to 1.11 U mL−1 and 11.11 to 476.11 U mL−1 with a relatively low detection limit of 0.004 U mL−1. Furthermore, this strategy avoided the addition of electron transfer mediator, which simplified the immunoassay procedure and decreased the analytical time.