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COUNTLESS teenagers have blamed their messy bedrooms on the propensity for everything in the Universe to become increasingly disordered鈥攖o have more 鈥渆ntropy鈥�. Now entropy has been persuaded to do some useful work鈥攄ragging DNA strands through a microscopic hairbrush.

Steve Turner and his colleagues at Cornell University in Ithaca, New York, built a sandwich of two glass plates with a tiny gap in between (see Graphic). One half of the gap was filled with a forest of pillars that formed long corridors 50 nanometres wide, while the other was left open. They filled the structure with saline solution, then used an electric field to pull DNA strands into the corridors. Left to their own devices, DNA coils up into tangles with maximum disorder, but the pillars forced them into ordered, low-entropy lines.

When the researchers turned off the electric field, any strands that still had one end dangling in the open slithered out of the lattice like a chain falling off a table鈥攕lowly at first, then with increasing speed. Strands that were wholly inside the lattice stayed put.

Turner insists that entropy is responsible, rather than some elastic property of the molecules causing them to spring back into a coiled state. 鈥淭here is no elastic stretching of the DNA going on,鈥� he says.

Since longer strands are more likely to have ends dangling out of the lattice, entropy could separate DNA strands of different lengths, hundreds of times faster than existing techniques. 鈥淭his method takes about a minute,鈥� says Turner. DNA-strand probes could also show up entropy differences within structures by migrating from one region to another.