A team of scientists including Ph.D. student Friedrich Schuler from the Laboratory of MEMS Applications at the Department of Microsystems Engineering (IMTEK) of the University of Freiburg in Germany has developed a method for dividing a DNA sample into thousands of tiny droplets. What sets it apart from previous methods is, above all, the fact that it is considerably easier to control and rapidly generates more than 10,000 droplets with a diameter of approximately 120 micrometers each. The entire process takes place on a rotating plastic disk the size of a DVD. The researchers presented the new method in an article published online on April 23, 2015 in the journal Lab on a Chip. The article is titled “Centrifugal Step Emulsification Applied for Absolute Quantification of Nucleic Acids by Digital Droplet RPA.” Carried by centrifugal force, a watery liquid flows through channels on the rotating disk to a chamber filled with oil. At the mouth of the channel, droplets tear off - similar to a dripping faucet. A bioreaction for the detection of DNA takes place in the droplets: They glow if they contain at least one DNA molecule, enabling the scientists to count the molecules with great precision. This is relevant for numerous clinical applications, such as cancer diagnostics, prenatal diagnostics, diagnosis of blood poisoning, or monitoring of HIV patients. The researchers use an especially fast detection reaction known as recombinase polymerase amplification for the first time ever in the droplets, reducing the time necessary for the entire procedure from more than two hours to less than 30 minutes. Moreover, the new method enables the entire sample fluid to be distributed among the droplets, without leaving residue in channels or tubes. That saves money and reduces the amount of effort necessary to prepare sample material.
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