The Lion lies down with the Lamb

The recent report from P. Guo at Purdue that RNA can be used as the building block for nanostructures(original article in Nano Letters, subscription probably required; news report) has generated rare unanimity between the Drexlerian and the nanobusiness wings of the nanotechnology movement. Remarkably, the achievement has united the Tom and Jerry of the nanotechnology blog world, TNTlog, and the Center for Responsible Nanotechnology. Is this excitement warranted?

Very much so, in my view. The advantage of DNA as a nanotechnological building block (as demonstrated in Seeman’s work) is that the self-assembly process between base-pairs that creates the duplex, double helix structure, is very straightforward to understand and model. This means that the design process, in which one deduces what sequence of bases is required to produce a given 3d structure, is highly tractable. Proteins exhibit a much richer range of useful three dimensional structures, but rational design involves a solution of the protein folding problem, which still remains elusive. RNA offers a middle way; RNA self-assembly is still governed by straightward base pairing interactions involving four bases in two complementary pairs. But RNA, unlike DNA, can fold and form loops and hairpins, giving a much richer range of possible 3d structures. Thus, using RNA, we could get the best of both worlds – the richness of potential self-assembled structures of proteins, with the computational tractability of DNA.

We should remember that neither DNA nanotechnology nor RNA nanotechnology is likely to yield mass-market products any time soon – nucleic acids are delicate molecules that remain enormously expensive. But these lines of research are just the sort of avenue that publically funded nanoscience should be supporting – visionary stuff that can excite both the Drexlerian radicals and the pragmatic nano-businessmen.

Attack of the nanopants

Howard Lovy reports a televised encounter between some nanopants and a sticky fluid, in which the nanopants came off the worse.

Nanopants (or nanotrousers to any local readers) are garments whose fabric has been treated with the textile treatments of the Nano-tex corporation to improve their resistance to staining. Nanopants have become a bit of a touchstone to where people stand in the controversial matter of deciding what nanotechnology actually is. To followers of the Drexlerian view of nanotechnology (MNT) they are a symbol of how the word nanotechnology has been debased to cover all kinds of mundane, incremental applications of technology, far removed from the original grand vision. The pro-MNT blogger Glenn Harlan Reynolds simply calls them fake. But Nano-tex, to the nanobusiness community, is a splendid example of how nanotechnology can transform even traditional industries. Where does the truth lie?

I looked up the Nano-tex patents, in an attempt to establish whether the nano in these pants is real or simply marketing hype. There are 18 of them, and it isn’t obvious which technology is used in which product, but the general idea is clear enough. A typical product will be a copolymer – two or more chemically different polymer chains that are chemically attached to each other. One type of polymer will be hydrophilic, and this will tend to stick to a cotton or wool fibre, and the other part is hydrophobic. These hydrophobic bits of the chain will arrange themselves away from the textile surface, presenting a water and stain resistant surface to the outside world.

Two questions – is this novel, and is it nanotechnology? From the point of view of a scientist (rather than a patent lawyer) it clearly isn’t that new. It’s the same basic idea as 3M’s ScotchgardѢ, invented in 1956 – this technology is also based on a copolymer, in this case an acrylic backbone on which water-repellant fluorocarbon side-chains are grafted. This works in just the same way as Nano-tex’s molecules – the acrylic backbone sticks to the fibre surface, leaving the water-repellant side-chains to coat the surface with a non-stick layer. But nonetheless, I do think it is nanotechnology, albeit of rather a rudimentary kind. A molecule has been defined with a specific architecture which codes the information it needs to form a specific nanoscale structure (in this case, sticky hydrophilic bits next to the textile surface, non-stick hydrophobic bits on the outside). It exploits the principle of self-assembly, which, as I explain in chapter 5 of my book Soft Machines, is the principle by which the sophisticated nano-machines of cell biology are constructed, and which we will learn to use in ever more sophisticated ways to make synthetic nano-devices.

But if nanopants really are nanotechnology, does that not imply that 3M have been doing nanotechnology since at least 1956, without using the label? Well, in this sense, yes. So the final lesson should probably be that the use of nano as a label for incremental products like this does owe a lot to marketing, but that doesn’t mean they don’t involve sophisticated technology. It’s just that other products without the nano label may in fact be just as nano-enabled.

Drexler responds

This morning brought a somewhat tetchy email from K. Eric Drexler, not entirely happy about my article in Physics World, The future of nanotechnology. There were three main complaints:

1. That he, Drexler, could not be held responsible for the “ridiculous artist’s concepts” that have become associated with his work. Thus my criticism of the nanosubmarine illustration isn’t a fair criticism of MNT. Actually, I have some sympathy with his predicament on this, in that I’m sure that the elementary errors that show up in the particularly silly image I chose wouldn’t be there if Drexler had had anything to do with it. Nonetheless, my criticism of these images does make one important point very clear – you shouldn’t expect macroscopic engineering design concepts to apply to directly to the nanoworld. Is this a fair criticism of MNT? I think it is – to quote from the preface of Nanosystems; “Molecular manufacturing applies the principles of mechanical engineering to chemistry”.

2. Next he argues that my statement that “Strong surface forces may make the moving parts of a NEMS device stick together and seize up” reflects a lack of study of the appropriate section of Nanosystems, chapter 10, which argues that very low friction is to be expected between atomically smooth diamond surfaces. It’s worth noting first of all that this statement in my article isn’t actually directed at MNT at all, but at top-down NEMS. Nonetheless, I do believe that the discussion in Nanosystems does substantially underestimate the problems of friction and dissipation at the nanoscale. This is a rather technical discussion, which I will enlarge on at a later time.

3. Finally, he objects that I have not proved my central contention, that biology is highly optimised for the nanoscale, pointing out that biology hasn’t been able to explore the space of non-aqueous molecular machine systems. This gets to the heart of the argument of Soft Machines. A crucial, though obvious, point, is that it only makes sense to talk about optimisation in the context of a particular environment, and what is optimised for ambient operation at 300 K in the presence of water is not the same as what is optimised for ultra-high vacuum at a temperature of 3 K. I wouldn’t exclude the possibility that MNT would work at 3 K in UHV, but I think that what works in ambient conditions is much more interesting, if only because medicine is likely to be such an important application of nanotechnology.

Soft Machines weblog

Welcome to the Soft Machines weblog, which I hope will be the more interactive part of the overall Soft Machines website. One purpose of the website is to publicise my book, of course, but I would also like to make it a useful resource on nanotechnology. I’m not going to try to be comprehensive – there are many other good resources on the internet and elsewhere. Instead I’ll give a personal view, from the perspective of a scientist working in the area, of what I think is really interesting. I’ll also use the web-site if I need to amplify points in the book, to report feedback to the book and my response to it, and if necessary to update and correct it. Early drafts of this material will probably make their first appearance on this weblog.