Effect of silica nanoparticles with different sizes on the catalytic activity of glucose oxidase.

In this work we present a strategy for the covalent immobilization of periodate oxidized glucose oxidase (IO(4)(-) - GOx) to aminated silica nanoparticles (ASNPs) modified on gold electrodes. Silica nanoparticles greatly enhanced the catalytic ability of GOx toward the oxidation of glucose and improved the electron transfer between the GOx and the electrode surface. ASNPs of varying size--that is 100, 80, 60, and 30 nm--were prepared, and they were used to fabricate biosensors. Electrochemical impedance spectroscopy (EIS) of ferrocyanide followed the assembly process and verified the successful immobilization of IO(4)(-) - GOx on ASNPs modified on gold electrodes. From the analysis of catalytic signals of biosensors using different sizes of ASNPs under the same conditions, the surface concentration of electrically wired enzyme (Gamma (ET)) was estimated and was found to increase with decreasing ASNPs size. Therefore, the sensitivity of biosensors using smaller ASNPs was higher than that using larger particles. Specifically, we utilized the ASNPs with optimal size (30 nm) to fabricate the glucose biosensor. The resulting electrodes showed a wide linear response to glucose at least to 6 mM and reached 95% of the steady-state current in less than 4 s with a sensitivity of 5.02 microA mM(-1) cm(-2) and a detection limit of 0.01 mM. The biosensor also showed excellent stability and good reproducibility.