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Nucleic Acid Extraction Instruments

Nucleic acid isolation/extraction usually includes; disrupting the cell membrane/wall, inactivating the nuclease activity, removing the proteins, precipitating the isolated nucleic acid and storage.[1]

So far, methods generally employed have been considered in two categories; as conventional ‘liquid-phase isolation’ and common  ‘solid-phase isolation’ which is highly appreciated in molecular biology field as a result of its practical use.

•Guanidinium  Acid -Phenol- Extraction method
•Alkaline Extraction method.
•Ethidium Bromide (EtBr)-Cesium Chloride (CsCl) Gradient centrifugation method.
•Oligp(dT)-Cellulose Chromatography method

‘Solid-phase isolation’ methods avoid the phase separation problem usually faced in ‘liquid-phase isolation’ methods, and are faster and more effective than conventional methods. Isolation of the nucleic acid is carried out in 4 main steps including; lysis, binding, washing and final elution steps.  First,  the sample  is lysed by lysis buffer solution. Using a buffer at a particular pH , the surface or functional groups on the solid/column are converted into a particular chemical form. Buffer conditions (pH and salt concentration) are optimised in order to achive the effective binding of nucleic acid to the column surface. Other compounds are removed in further washing steps using the washing buffer.  The bound nucleic acid is then eluted with the aid of water or TE buffer. Nowadays, most of the commercial extraction kits available in the market are based on this principle. Depending on the pH and salt content of the buffer, the binding and release of the nucleic acis is achieved. The main solid-surface (suport) materials used in sold-phase extraction systems are usually; silica matrix, glass particles, diatomite, magnetic particles or anion-change surfaces.

The extraction methods where magnetic particles/beads are employed, are much quicker, simpler and more effective than other methods via their easy integration to the  automated systems leading to possibility of large-scale studies. Magnetic isolation is based on the separation of magnetic particles by applying a magnet.  As the cells with adequate magnetic field can be separated directly, the magnetic complexes composed of non-magnetic cells and magnetic particles may be used for the indirect separation of cells.
The magnetic extraction method applied for the isolation of nucleic acids is carried out in 3 main steps:

•The magnetic complex is achieved by the addition of magnetic particles and further incubation.
•The undesired compounds/contaminants such as proteins are removed by washing the magnetic complex with the washing buffer. 
•The nucleic acid is released from the magnetic complex by the elution step.

Magnetic-supermagnetic particles, magnetic colloids, magnetoliposomes are commonly used magnetic markers. Today, most of the automated nucleic acid extraction systems usually employ the magnetic particles technology.


Annotated Bibliography

1.Siun Chee Tan and Beow Chin Yiap, DNA, RNA, and Protein Extraction: The Past and The Present, Journal of Biomedicine and Biotechnology Volume 2009,  Article ID 574398.
2.Cell Separation and Protein PuriTcation (1996) Oslo, Norway: Dynal. 165 pp.
3.Safarik and Safarikova  M (1999) Use of magnetic techniques for the isolation of cells. Journal of Chromatography B 722: 33d53.
4.Olsvik , Popovic T, Skjerve E et al. (1994) Magnetic separation techniques in diagnostic microbiology. Clinical Microbiology Reviews
5.Matthias Franzreb, Martin Siemann-Herzberg, Timothy J. Hobley, et al. Protein purification using magnetic adsorbent particles[J]. Appl Microbiol Biotechnol 2006 70: 505-516.