Description:

Using a forest of nanofabricated pillars so small (about 35 nanometers (nm) in diameter,  spaced 125nm apart) that DNA molecules can only slip through lengthwise, Cornell University researchers have demonstrated the existence of an entropic recoil force that causes the molecules to move from a tight space into a more open one.

In these experiments the DNA molecules are pulled into the dense array of pillars by an electric field. If the field is removed before a molecule is all the way in, it will recoil back into the open space and resume its spherical shape. Physicists have theorized that it is an entropic force related to the confinement of the molecule in a narrow tube that causes the recoil. Entropy is a measure of the amount of disorder in a system, and an entropic force would tend to move things toward the most disorderly arrangement. In this case, Turner explains, that would be the one in which the molecule can assume many different configurations -- that is, free in water -- rather than the one in which it is confined in a narrow tube.

The device is made of silicon nitride, which is transparent to visible light. The DNA molecules themselves are too small to be seen by visible light, but they are stained in a way to make them fluorescent so that the light they give off can be observed.
 

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