DNA and self-organisation in the nanoworld

On the BBC News website and elsewhere there are reports of an interesting paper just published in Nature Nanotechnology on the use of DNA in the production of next-generation computer chips. This has to do with the ability of genetic material to self-organise or self-assemble chemical compounds into complex structures.

As a journalist I’ve written much about nanoscience and technology, and the topic of self-assembly has come up on many occasions. However, I’ve often been frustrated with the lack of attention by scientists and science communicators to explaining nanoscale self-assembly comprehensibly and accurately at a basic level. The process often comes across as something magical or vital, when the reality is more prosaic.

A full and proper account of self-assembly is well beyond the scope of a hastily written blog post*, but I shall attempt here to make one or two relevant points.

What IBM researcher Ryan Kershner and his colleagues have done in their Nature Nanotechnology study is get an engineered “DNA origami” to organise itself in such a way that it could serve as a scaffold for electronic components spaced far more closely than can be achieved with current industrial techniques.

In recent years there have been published a number of similar studies, and significant progress is being made in the field. The motivation for this is the increasing difficulty in further miniaturising microchip production using traditional top-down approaches which involve the time consuming etching away of material, or the positioning of components onto substrates with the aid of highly sophisticated and hugely expensive tools.

Today’s microprocessors, for example, have transistor spacings of around 45 nanometres (billionths of a metre), and we are currently struggling to get this down to 22 nanometres. With self-assembly techniques we could in principal reduce the spacing to less than 10 nanometres. It all depends on the nature of the chemical scaffold used in the fabrication process.

What exactly is “self-assembly”? Put simply, self-assembly is defined as a process in which a disordered system of pre-existing chemical components forms an organised structure as the result of local interactions among the components, without any external direction. This typically involves an attraction between molecules arising from their structure. A molecule may, for example, have bits prodding out from a central core, which are terminated in chemical elements that adhere to bits protruding from other molecules. You can think of it as a kind of chemical velcro.

Nature excels at building complex structures from materials available in the environment. We tend to associate this with life, but there are a number of inorganic processes which fit the description of self-assembly, and in certain cases it can be difficult to distinguish between the two. For example, this has in the past led to claims regarding the discovery of bacteria in meteorites from Mars. These were subsequently challenged by geochemists who showed that the phenomenon could be explained without recourse to biology.

As far as nanotechnology is concerned there is considerable interest in using DNA as a chemical scaffold, and this is because we know so much about the molecule. But nanoscale self-assembly has been demonstrated in systems that have nothing to do with DNA, and it may be that future microchips are designed and built using scaffolds radically different from the double helix structure that underpins life.

With self-assembly there is no need to invoke concepts such as “cooperation” or “design”, in the way we normally think of them as the result of human intention. Note that I’m also guilty of this (e.g., “Nature excels…”). Maybe we need to develop a new language for describing such things. For now, however, we are stuck with what we have, and must instead qualify our use of vitalistic terminology when discussing non-sentient phenomena.

* I was recently invited by a US-based scientist to work with him on a popular presentation of nanotechnology. It’s early days, and we have yet to put together a pitch to send to publishers. Watch this space!