Sensitive fluorescent probes for determination of hydrogen peroxide and glucose based on enzyme-immobilized magnetite/silica nanoparticles

Sensitive fluorescent probes for the determination of hydrogen peroxide and glucose were developed by immobilizing enzyme horseradish peroxidase (HRP) on Fe(3)O(4)/SiO(2) magnetic core-shell nanoparticles in the presence of glutaraldehyde. Besides its excellent catalytic activity, the immobilized enzyme could be easily and completely recovered by a magnetic separation, and the recovered HRP-immobilized Fe(3)O(4)/SiO(2) nanoparticles were able to be used repeatedly as catalysts without deactivation. The HRP-immobilized nanoparticles were able to activate hydrogen peroxide (H(2)O(2)), which oxidized non-fluorescent 3-(4-hydroxyphenyl)propionic acid to a fluorescent product with an emission maximum at 409 nm. Under optimized conditions, a linear calibration curve was obtained over the H(2)O(2) concentrations ranging from 5.0 x 10(-9) to 1.0 x 10(-5) mol L(-1), with a detection limit of 2.1 x 10(-9) mol L(-1). By simultaneously using glucose oxidase and HRP-immobilized Fe(3)O(4)/SiO(2) nanoparticles, a sensitive and selective analytical method for the glucose detection was established. The fluorescence intensity of the product responded well linearly to glucose concentration in the range from 5.0 x 10(-8) to 5.0 x 10(-5) mol L(-1) with a detection limit of 1.8 x 10(-8) mol L(-1). The proposed method was successfully applied for the determination of glucose in human serum sample.