Templated synthesis of monodisperse mesoporous maghemite/silica microspheres for magnetic separation of genomic DNA

A novel method is described for the preparation of superparamagnetic mesoporous maghemite (gamma-Fe2O3)/silica (SiO2) composite microspheres to allow rapid magnetic separation of DNA from biological samples. With magnetite (Fe3O4) and silica nanoparticles as starting materials, such microspheres were synthesized by the following two consecutive steps: (1) formation of monodispersed organic/inorganic hybrid microspheres through urea-formaldedyde (UF) polymerization and (2) removal of the organic template and phase transformation of Fe3O4 to gamma-Fe2O3 by calcination at elevated temperatures. The as-synthesized particles obtained by heating at temperature 300 degrees C feature spherical shape and uniform particle size (d(particle) = 1.72 mu m), high saturation magnetization (M-s = 17.22 emu/g), superparamagnetism (M-r/M-s = 0.023), high surface area (S-BET = 240 m(2)/g), and mesoporosity (d(pore) = 6.62 nm). The composite microsphere consists of interlocked amorphous SiO2 nanoparticles, in which cubic gamma-Fe2O3 nanocrystals are homogeneously dispersed and thermally stable against gamma- to alpha-phase transformation at temperatures up to 600 degrees C. With the exposed iron oxide nanoparticles coated with a thin layer of silica shell, the magnetic microspheres were used as a solid phase adsorbent for rapid extraction of genomic DNA from plant samples. The results show that the DNA templates isolated from pea and green pepper displayed single bands with molecular weights greater than 8kb and A(260)/A(280) values of 1.60-1.72. The PCR amplification of a fragmenten coding the endogenous chloroplast ndhB gene confirmed that the DNA templates obtained were inhibitor-free and amenable to sensitive amplification-based DNA technologies. (C) 2010 Elsevier B.V. All rights reserved.