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"I adopt this mobile phone as my first-begotten son ... "

You may have wondered how much smaller mobile phones can get. Really, really small, is the answer, on the inside at least, thanks to some very cool research being done by MIT, the University of Illinois, and the R&D team at DuPont.

A group of scientists has found a way of using DNA to sort carbon nanotubes according to their conductivity, a discovery that will have huge implications for electronics design - even if the impact on the battery life of our mobile phones is still some way off.

Because of their electrical properties, carbon nanotubes have the potential to be used as the building blocks in a broad range of electronic applications, including highly sensitive medical diagnostic devices and really, really tiny transistors - as much as 100 times smaller than those in today's microchips.

The problem is that when they are made, all the different types of nanotube are mixed in together. Sorting them into groups of uniform conductivity has proved tricky, to say the least, and unless they can be sorted, they are no use to nanoscale electronic engineers.

See fig. 1 - unsorted nanotubes in solution appear in black (far left). Conducting nanotubes are pinkish in color, semiconducting ones greenish.

The project began when DuPont Central Research & Development scientists discovered (presumably not by accident ... ) that single-stranded DNA strongly interacts with carbon nanotubes to form a stable DNA-carbon nanotube hybrid that effectively disperses carbon nanotubes in an aqueous solution.

DuPont then hooked up with a multi-disciplinary team of scientists from MIT and the University of Illinois to tackle the work to the next stage. This next part we have had to take pretty much on faith, as we are neither DNA nor nanotech experts over here.

They found that a particular sequence of single stranded DNA self-assembles into a helical structure around individual carbon nanotubes. And since carbon nanotube-DNA hybrids have different electrostatic properties, depending on factors such as the nanotubes' diameter and electronic properties, they can be separated and sorted using anion exchange chromatography.

The technique can be used to separate metallic carbon nanotubes from semiconducting carbon nanotubes, both which are created during nanotube production. The technique also can sort semiconducting carbon nanotubes by diameters, an important element in nanoelectronic applications, we are told.