The longer the DNA molecule, the faster
In tiny fluid channels long DNA molecules are flowing faster than short ones. This perception may lead to new methods of sorting and separating biomolecules like DNA in size. This turns out to be the result of research by scientists of the Delft University of Technology and the Foundation for Fundamental Research on Matter (FOM) that will be published on Monday 28 August 2006 in the Proceedings of the National Academy of Sciences (PNAS).
The way biomolecules like DNA are moving in tiny fluid channels is of notable importance to modern applications in bioanalysis. The so-called ‘labs-on-a-chip’ are operating particularly efficient by having flow small quantities of fluid and biomolecules through these tiny fluid channels (nanochannels) and to analyse them. By now, it is possible to create fluid channels that are as tiny as one single DNA molecule.
Postdoc Derek Stein, student Wiepke Koopmans, PhD student Frank van der Heijden and leader of the research team Cees Dekker of the Kavli Institute of Nanoscience of the Delft University of Technology and FOM-Foundation had DNA molecules flow through rectangular fluid channels, only a few micrometers in height, by way of difference in pressure. It appeared that DNA molecules of different lengths are flowing through the channels in a different pace. The longer the molecule, the faster it moves.
This effect can be explained by the enormous number of shapes that a flexible polymer like DNA may adopt. The (randomly) thermal movement of a polymer provides the polymer to look like a loosely rolled up ball of wool. The longer the molecule, the larger the ball will be on average. Large molecules (balls) are more often to be found halfway the flow through the channel than small molecules (balls). The pace of flow is higher halfway the channel than at the edges, so that long DNA molecules will have a higher pace than the short molecules.
As the pace of the DNA molecules is dependent on their length, it is possible to sort them in size with the aid of nanochannels. Usually, the sorting takes place by way of gel electroforese. However, the rectangular channels that the researchers in Delft are using, offer a simpler and better adjustable method of separation at the level of one single molecule and without extra molecular marking. Moreover, it is possible to separate very long molecules, which is yet very difficult by way of gel electroforese.
The behaviour of the DNA molecules becomes even more unusual if the size of the channels is increasing. In channels less than one micrometer in height, molecules of all sizes will eventually reach the same pace. This result is explained by the extreme nearness of the walls, which will limit the number of shapes that a molecule may adopt. All molecules then move like flattened balls that are pressed together.
For more information, please contact :
Prof.dr. Cees Dekker, phone: (015) 278 60 94.
Dr. Derek Stein.
Frank Nuijens, public relations department, phone: (015) 278 42 59.