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DNA Extraction and Quantitation for Forensic Analysts

Magnetic Beads

The use of magnetic beads is another solid phase extraction method.

These methods:

  • Can be automated
  • Increase throughput
  • Demonstrate the ability to remove amplification inhibitors
  • Use no hazardous chemicals.

These kits can also be used as adjuncts to traditional methods, when additional clean-up is warranted.

The principle underlying magnetic bead procedures involves attracting DNA to magnetic beads, holding the beads in place using a magnetized source, such as a rack or tube holder, and washing away other components of the sample.

Invitrogen's ChargeSwitch® Technology (CST®) involves the use of magnetic beads whose surface bears a charge that can be switched based on the pH of the surrounding buffer environment. At low pH, the beads are positively charged, attracting the negatively charged DNA molecules and allowing proteins and contaminants to be removed by washing.

The DNA IQ™ System by Promega uses silica-coated magnetic beads. DN™ was designed for automation on robotic systems. The quantity of beads used in the procedure defines the binding capacity, which is approximately 100ng of DNA. This relative quantitative capability makes it ideal for databasing and paternity applications because consistent quantities of DNA are isolated. The DNA IQ™ kit contains the proprietary resin and several specialized buffers, including lysis, wash, and elution.

Photo of magnetic beads
National Institute of Justice (NIJ) (see reuse policy).

The EZ1™ System by Qiagen also uses silica-coated magnetic beads and designed to be used with a proprietary EZ1 robot. Large quantities of genomic DNA can be recovered and the robots have capacity to process up to 14 samples at one time. Traditional extraction programs are loaded on the robot, but they can also be customized to a specific laboratory need such as samples with large volumes. The EZ1™ kit contains the proprietary beads and several specialized buffers, including lysis, wash, and elution all pre-loaded in a strip that can be easily inserted into the robot.

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