Fabrication of mono-sized magnetic anion exchange beads for plasmid DNA purification

Mono-sized magnetic polyglycidyl methacrylate (PGMA) microspheres cross-linked by divinylbenzene were fabricated by the dispersion polymerization and penetration-deposition method. The magnetic beads were nonporous, spherical, and mono-sized (1.0 microm). Moreover, it was superparamagnetic with a saturation magnetization of 16.5 emu/g. The prepared magnetic beads were then functionalized with high-density amino groups and used as anion exchangers to capture plasmid DNA from concentrated bacterial lysates of Escherichia coli without treatment with ribonuclease A. The adsorption capacity of plasmid DNA reached 90 microg/mg resin in the buffer solution of pH 6.5 and 0.5 mol/l NaCl content. The product was of high recovery yield (91.7% DNA) and of high purity with almost 100% protein and 62.5% RNA removal. Recycled use of the magnetic material for plasmid purification exhibited stability of the magnetic microspheres. The magnetic beads were also effective in the purification of DNA from original crude bacterial lysates. For example, 19.4 microg plasmid DNA (A(260)/A(280)=1.90) was isolated from 1.5 ml cell culture. The results presented in this article suggest that the prepared mono-sized magnetic adsorbent is suitable for high efficient isolation and purification of plasmid DNA from crude feedstock with high recovery yield and purity.