Silica magnetic beads can bind nucleic acids controlled by three competing effects:   weak electrostatic repulsion forces, dehydration, hydrogen bond formation(Melzak et al., 1996). By the support of guanidine salts, detergents, or proteinase K,   the nucleic acids are released from the biological samples, such as cell,   tissues, plant and microorganism. Consequently, the released nucleic acids specially   bind to silica magnetic beads forming DNA/RNA-beads complexes under the   condition of chaotropic salts (e.g. guanidine salts,   perchlorate salts and isopropanol etc.). Through magnetic separation, the   complexes can be rapidly collected from the biological sample lysis solution.   Proteins, other impurities and any salts are washed away by several washing   steps with different washing buffers. Finally, the pure DNA/RNA can be easily   eluted from the beads by TE(10mM Tris, 1mM EDTA, pH8.0) or ddH2O(pH>7.0).   From the basic principle described above, we can get the optimal reagents and   operating process by adjusting parameters including pH value, salt   concentration, kind of chaotropic or kosmotropic salt, detergent   concentration, which involve the lysis buffer, binding buffer, washing buffer and elution buffer.

At present, the chemical constituents in nucleic acids isolation kits differ from different company, but all these kits are   mainly divided into two groups, chaotropic salt system(Boom et al., 1990), kosmotropic salts system(Lee et al., 2008), according to the salts used for binding.   The chaotropic salts, such as iodized salts, perchlorate, and guanidine salts, which have the ability to disrupt the regular hydrogen bond structures. The high concentration of chaotropic salts let proteins   denature, nucleicacidase lose activity, and help silica magnetic beads selectively bind nucleic acids. In contrast, the Kosmotropic   salts have much stronger interactions with water and promote hydrophobic   interactions, these including sodium sulfate and ammonium sulfate, etc. 

The novel method of nucleic acids   isolation based on silica beads can be used to extract DNA/RNA with different   length from wide varieties of biological samples. For examples, isolation   genomic DNA from plant(Zhang et   al., 2007), fungi(Rittich et   al., 2006), blood(Duarte et   al., 2010), forensic tissue(Nagy et   al., 2005); and isolation RNA from cells(Lee et al., 2008), plant(Ding et   al., 2008); and isolation plasmid DNA from bacterial   cells(Chiang et   al., 2006); meanwhile certain reagents match silica   magnetic beads for DNA/RNA isolation also listed in these referred publications.  

Fig. The sketch of application of silica magnetic   beads on nucleic acids isolation

References

Boom R., Sol C., Salimans M., Jansen C., Wertheim-van Dillen P., Van der   Noordaa J. (1990) Rapid and simple method for purification of nucleic acids.   Journal of Clinical Microbiology 28:495.

Chiang C.L., Sung C.S., Chen C.Y. (2006) Application of silica-magnetite   nanocomposites to the isolation of ultrapure plasmid DNA from bacterial   cells. Journal of Magnetism and   Magnetic Materials 305:483-490.

Ding L.-W., Sun Q.-Y., Wang Z.-Y., Sun Y.-B., Xu Z.-F. (2008) Using   silica particles to isolate total RNA from plant tissues recalcitrant to   extraction in guanidine thiocyanate. Analytical Biochemistry 374:426-428.

Duarte G.R.M., Price C.W., Littlewood J.L., Haverstick D.M., Ferrance  J.P., Carrilho E., Landers J.P. (2010) Characterization of dynamic solid   phase DNA extraction from blood with magnetically controlled silica beads.   Analyst 135:531-537.

Lee M., Huh N., Kim J.H. (2008) Isolation of total RNA from Escherichia   coli using kosmotropic Hofmeister salts. Analytical Biochemistry 381:160-162.   DOI: Doi 10.1016/J.Ab.2008.06.015.

Ligozzi M., Fontana R. (2003) Isolation of total DNA from bacteria and   yeast. African Journal of Biotechnology 2:251-253.

Melzak K., Sherwood C., Turner R., Haynes C. (1996) Driving forces for   DNA adsorption to silica in perchlorate solutions. Journal of Colloid and   Interface Science 181:635-644.

Nagy M., Otremba P., Krüger C., Bergner-Greiner S., Anders P., Henske   B., Prinz M., Roewer L. (2005) Optimization and validation of a fully   automated silica-coated magnetic beads purification technology in forensics.   Forensic Science International 152:13-22.

Rittich B., Spanova A., Horak D., Benes M.J., Klesnilova L., Petrova K.,   Rybnikar A. (2006) Isolation of microbial DNA by newly designed magnetic   particles. Colloids and Surfaces   B-Biointerfaces 52:143-148. DOI: DOI 10.1016/j.colsurfb.2006.04.012.

Zhang Z.C., Cui Y., Wan Q.H. (2007) Surface modification of magnetic   silica microspheres and its application to the isolation of plant genomic   nucleic acids. Chinese Journal of   Analytical Chemistry 35:31-36.