Magnetite-Containing Spherical Silica Nanoparticles for Biocatalysis and Bioseparations

Abstract

The simultaneous entrapment of biological macromolecules and nanostructured silica-coated magnetite in sol−gel materials using a reverse-micelle technique leads to\na bioactive, mechanically stable, nanometer-sized, and\nmagnetically separable particles. These spherical particles\nhave a typical diameter of 53 ± 4 nm, a large surface area\nof 330 m<sup>2</sup>/g, an average pore diameter of 1.5 nm, a total\npore volume of 1.427 cm<sup>3</sup>/g and a saturated magnetization (<i>M</i><sub>S</sub>) of 3.2 emu/g. Peroxidase entrapped in these\nparticles shows Michaelis−Mentan kinetics and high\nactivity. The catalytic reaction will take place immediately\nafter adding these particles to the reaction solution. These\nenzyme entrapping particles catalysts can be easily separated from the reaction mixture by simply using an\nexternal magnetic field. Experiments have proved that\nthese catalysts have a long-term stability toward temperature and pH change, as compared to free enzyme\nmolecules. To further prove the application of this novel\nmagnetic biomaterial in analytical chemistry, a magnetic-separation immunoassay system was also developed for\nthe quantitative determination of gentamicin. The calibration for gentamicin has a working range of 200−4000 ng/mL, with a detection limit of 160 ng/mL, which is close\nto that of the fluorescent polarization immunoassay (FPIA)\nusing the same reactants.