Electromagnetic Technique to Lower Cost of Genome Mapping

Mapping of individual human genomes is hampered by techniques incapable of coping with the more than three billion base pairs that have to be sequenced. To solve this problem and to reduce the cost per patient to $1,000 or less (as requested by the [U.S.] National Institutes for Health), investigators at Brown University (Providence, RI, USA) combined the standard method of electrophoresis, voltage-driven DNA translocation through nanopores, with a novel application of magnetic field technology. The main drawback of the electrophoresis technique has been the high speed at which the DNA molecules move through the site of base pair sequencing, which leads to inaccurate determinations.

The first step in the new technique was to attach DNA strands to 2.8-micron diameter beads using the well-known avidin-biotin binding method. The strands were then placed in an electric field that induced them to move through a gel with nanopores only 10 nm in diameter. While the DNA strands could pass through the pores, the beads could not. Next, a magnetic field was applied in the direction opposite to the electric field, and the strands were slowly pulled back out of the pores. At this time the base pair sequences could be easily and clearly identified. Many individual DNA strands could be handled at the same time.

Senior author Dr. Xinsheng Sean Ling, professor of physics at Brown University said that the investigators called their process "reverse DNA translocation" because, "The DNA is essentially caught in a tug-of-war. And the speed of translocation will be controlled not solely by the electric field but by striking some balance between the magnetic and the electric fields. From there, we can tune it to dictate the speed."

"When it comes to sequencing anyone's genome, you need to do it cheaply, and you need to do it quickly," explained Dr. Ling. "This is a step in that direction."

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