BioEd Online

US researchers have woven DNA into a net that expands and contracts¹. It could be used as a nano-filter or in biological sensors.

It might even be the basis of a computer that has as its components lumps of metals or semiconductors just a few millionths of a millimetre - nanometres - wide. The switchable DNA net could turn electrical communication between these devices on and off by altering the distance between them.

In a sensor containing an array of proteins that latch onto other biological molecules, the mesh might activate or deactivate the process by plugging and unplugging the cavities of sensor molecules that bind their targets.

DNA is an ideal construction material for nanotechnology. It can be programmed to stick together in prescribed structures - like minuscule girders with matching locks and keys at their ends.

For example, the mesh-making team - Hao Yan and colleagues at Duke University in Durham, North Carolina - has also devised X-shaped DNA tiles that link up into a square grid². Proteins can be arranged on this scaffold, by hooking them to the middle of an X. Coating the grid with silver creates a lattice of nano-wires, which could be used in ultra-miniature electronic circuits.

To make such grids switchable, Yan and colleagues build into some of the strands sections of DNA that can lengthen and shorten like pistons. Each is a short stretch of double-helical DNA interrupted by a small loop where one of the strands bulges out and twists around itself.

This loop can be straightened out by feeding it 'fuel': a short snippet of single-stranded DNA. A fuel strand strips away the segment of DNA that was holding the two sides of the loop together, leaving the loop exposed. The researchers then feed in a second short, single strand of DNA, which inserts itself, opening up the loop. In this way, the DNA girder becomes about 6.8 nanometres longer.

The process can be reversed with a second fuel strand that snips out the inserted strand and allows the loop to re-form, followed by a second strand that binds the two sides of the loop firmly back together again.