Direct electrochemistry and biocatalysis of glucose oxidase immobilized on magnetic mesoporous carbon

A magnetic mesoporous carbon material (i.e., mesoporous iron oxide/C, mesoFe/C) is synthesized for protein immobilization, using glucose oxidase (GOx) as model. Transmission electron microscopy images show that mesoFe/C has highly ordered porous structure with uniform pore size, and iron oxide nanoparticles are dispersed along the wall of carbon. After adsorption of GOx, the GOx-mesoFe/C composite is separated with magnet. The immobilized GOx remains its natural structure according to the reflection-absorption infrared spectra. When the GOx-mesoFe/C composite is coated on a Pt electrode surface, the GOx gives a couple of quasireversible voltammetric peaks at -0.5 V (vs. saturated calomel electrode) due to the redox of FAD/FADH(2). The electron-transfer rate constant (k (s)) is ca. 0.49 s(-1). The modified electrode presents remarkably amperometric response to glucose at 0.6 V. The response time (t (95%)) is less than 6 s; the response current is linear to glucose concentration in the range of 0.2-10 mM with a sensitivity of 27 mu A mM(-1) cm(-2). The detection limit is 0.08 mM (S/N = 3). The apparent Michaelis-Menten constant (K (m) (app) ) of the enzyme reaction is ca. 6.6 mM, indicating that the GOx immobilized with mesoFe/C has high affinity to the substrate.