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Magnetic bead technology has been used for DNA isolation from biological samples with more advanced techniques in recent years due to the breakout of public health-threatening diseases requiring prompt diagnosis of the suspected disease. Isolation and amplification of the specific biomolecules is the downstream phase of numerous molecular methods such as detection, cloning, sequencing, amplification, hybridisation, cDNA synthesis, etc. and the presence of other cellular components and contaminating materials in the sample mixture makes this procedure very challenging.

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Nevertheless, with the application of surface-coated magnetic beads in recent years aligned with an appropriate buffer system has offered many advantages over the conventional DNA isolation techniques which make the procedure time and cost benefit.

DNA isolation procedure, Surface coating and buffer for DNA isolation

DNA detection is a sensitive method which takes less time to finish the procedure compared to the immunological methods. DNA extraction comprises several steps namely cell lysis/disruption, inactivation of cellular nucleases, removal of protein and contaminants and extraction/purification of nucleic acid.

Surface coating properties of the beads and the buffer play a major role in the DNA isolation procedure as the former highly affects the specificity of the beads. Basically, Silica, silicon-dioxide, is used to coat magnetic microbeads for DNA isolation. The binding of DNA to silica has been studied and optimized to understand how certain chaotropes, pH and ion concentrations play a role in better binding of DNA to magnetic beads coated in silica. Chaotropes have been found to be crucial for DNA isolation because they disrupt hydrogen bonds in solution which creates a favorable environment for DNA binding to silica. Many kits use either guanidinium or thiocyanate as chaotropes to aid in nucleic acid binding to silica on magnetic beads.

Magnetic beads for DNA isolation in the research or clinical laboratory

Magnetic beads are a collection of uniform particles (500 nm to 500 mm in diameter) which are typically made with composites containing nanoparticles of magnetite. When exposed to a magnetic field these beads have a magnetic “moment” by which they can be directed to the side of their vessel after nucleic acid binding and elution step to pour away the remaining solvent and collect a pure DNA sample ready for quantification and analysis.

Using the appropriate kit and protocol various types of DNA can be isolated from cells, tissue, or viruses, and blood samples. Magnetic separation techniques are scalable making them useful for clinical settings, and even for industry laboratories which do large scale purifications and optimizations. It is common to use different sizes of racks for 96 or 24 well plates. But the use of modern magnetic beads DNA separation systems allows for working with volumes up to tens of liters.

Advantages of magnetic beads for DNA purification

Using magnetic beads provides a quick, simple and efficient procedure for DNA isolation as it avoids shear forces leading to the degradation of the nucleic acids and the risk of cross-contamination.  Magnetic beads also isolate DNA directly from crude sample materials such as blood, tissue homogenates, cultivation media, water, etc. Besides, the magnetic properties can be modified based on the solid materials so they can be removed easily even from viscous sample suspensions and small-volume samples. The efficiency of magnetic beads DNA separation is especially suited for large-scale purifications. Magnetic beads also serve as a basis of various automated low-to high-throughput procedures that allow saving time and money without requiring columns.

Conclusion

Typical protocols for DNA purification in the field have previously included columns, centrifugation steps, and several types of buffers at various steps that cannot always be fully removed, leaving residual buffers and unwanted biological molecules at each step. Magnetic beads, however, offer a consistent protocol in which the sample is exposed to a magnetic force. A simple magnet may work for small scales, but a constant and well defined force can be applied -even at the tens of liters scale- by using modern magnetic separation systems.  There is less room for error, and the yield is higher. More advanced magnetic separation systems for biological separation are made specifically to be gentle on samples and separate quickly and efficiently with a safe magnetic force toward DNA-containing samples.

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Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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