Bifunctional Porous SiO2 Complex Nanoparticles with Properties of Enzymatic Catalysis and Optical Oxygen Sensing

The porous fluorescent SiO2 nanoparticles encapsulating photosensitizer Ru(bpy)3Cl2 were prepared by Stöber method and used as a carrier to immobilize glucose oxidase (GOD) to form the bifunctional porous SiO2 complex nanoparticles (BPSCNp) with the properties of enzymatic catalysis and optical oxygen sensing. The optimal immobilization conditions are as follows: hexadecyltrimethyl ammonium bromide (APTES) concentration of 2% (v/v), glutaraldehyde (GA) concentration of 1.0% (v/v), and pH of 6.5, GOD amount of 4.0 mg in 40 mg of carrier. BPSCNp showed maximal catalytic activity at pH 6.0 and 50 °C. After immobilization, the thermal storage and operation stability of GOD were improved remarkably. After kept at 4 °C for 30 days, BPSCNp and free GOD retained 68% and 35% of initial activity, respectively. BPSCNp maintained 58% of its initial activity after 7 consecutive operations and 30% after 15 consecutive operations. The fluorescence of BPSCNp could be quenched effectively by oxygen. There was a good linear relationship between tanφ0/tanφ and O2 concentration in the range of 0 to ca. 90%. BPSCNp had a highly reproducible response to oxygen with the response time of 20 s. BPSCNp might be used as the sensing material and have potential application in multi parameter fiber optic biosensor based on enzyme catalysis and oxygen consumption.