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

摘要

A novel method is described for the preparation of superparamagnetic mesoporous maghemite (γ-Fe_2O_3)/silica (SiO_2) composite microspheres to allow rapid magnetic separation of DNA from biological samples. With magnetite (Fe_3O_4) and silica nanoparticles as starting materials, such microspheres were synthesized by the following two consecutive steps: (1) formation of mono-dispersed organic/inorganic hybrid microspheres through urea-formaldedyde (UF) polymerization and (2) removal of the organic template and phase transformation of Fe_(3)O_4 to γ-Fe_2O_3 by calcination at elevated temperatures. The as-synthesized particles obtained by heating at temperature 300 ℃ feature spherical shape and uniform particle size (d_(particle) = 1.72 μm), high saturation magnetization (M_s=17.22emu/g), superparamagnetism (M_r/M_s=0.023), high surface area (S_(BET)=240m~2/g), and mesoporosity (d_(pore)=6.62 nm). The composite microsphere consists of interlocked amorphous SiO_2 nanoparticles, in which cubic γ-Fe_2O_3 nanocrystals are homogeneously dispersed and thermally stable against γ- to α-phase transformation at temperatures up to 600 ℃. 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 8 kb and A_(260)/A_(280) values of 1.60-1.72. The PCR amplification of a fragment encoding the endogenous chloroplast ndhB gene confirmed that the DNA templates obtained were inhibitor-free and amenable to sensitive amplification-based DNA technologies.