BIGGER is not always better. Anyone who doubts that has only to look at the explosion of computing power that has marked the past half-century. This was made possible by continual shrinkage of the components from which those computers are made—and that success has, in turn, inspired a search for other areas where shrinkage might also yield dividends.
One such, which has been poised delicately between hype and hope since the 1990s, is nanotechnology. Though what people mean by this has changed over the years—to the extent that cynics might be forgiven for wondering if it is more than just a fancy rebranding of the word “chemistry”—nanotechnology did originally have a fairly clear definition. It was the idea that machines with moving parts could be made on a molecular scale. And this year’s Nobel prize for chemistry has been awarded to three researchers, Jean-Pierre Sauvage, Sir Fraser Stoddart and Bernard Feringa, who have never lost sight of that original definition.
Dr Sauvage’s contribution was to link atoms together in a new and potentially useful way. Conventional molecules are held together by bonds in which electrons from neighbouring atoms pair up. Sometimes (such as the case of benzene) the result is an atomic ring. Dr Sauvage realised that rings of this sort might be linked up in the way that the links of a metal chain are, and a molecule thus created that is held together mechanically, rather than by conventional chemical bonds (though these remain necessary to the integrity of the links themselves). In 1983 his research group at Strasbourg University, in France, managed to do this and, 11 years later, they demonstrated a miniaturised molecular motor that consisted of two rings linked in this way. Applying energy to it causes one of the rings to rotate around the other.
Sir Fraser was awarded his third of the prize for work on a similar miniature machine. In 1991 he and his colleagues at Northwestern University in Illinois managed to thread a tiny molecular axle through a ring-shaped molecule. Heating the result caused the ring to slide between the ends of the axle, producing a molecular shuttle. Since then his group has diversified into other machines, including an atomic-scale lift, artificial muscles and even a simple mechanical computer made of molecule-sized components.
The true desideratum of nanotechnology research, however, has always been a molecular motor that rotates around an axle rather than just sliding up and down it. And it was for creating such a molecule, in 1999, that Dr Feringa will receive his share of the prize. His crucial insight was to work out how to make the ring spin reliably in a single direction—for a motor that might choose, at random, to turn either way when you start it up is not much use. By 2011 his team at Groningen University, in the Netherlands, had grown sufficiently dexterous to assemble a “nanocar”. This consists of a molecular chassis connected to four spinning wheels which move the car (very slowly) across a surface.
How long it will take to turn any of these inventions into useful products remains to be seen. Optimists talk of manufacturing molecule-sized machines ranging from drug-delivery devices to miniature computers, but nanotechnology is a field that has been puffed up repeatedly by both researchers and investors, only to deflate in the face of practical difficulties.
There is, though, good reason to hope it will work in the end. This is because, as is often the case with human inventions, Mother Nature has got there first. One way to think of living cells is as assemblies of nanotechnological machines. For example, the enzyme that produces adenosine triphosphate (ATP)—a molecule used in almost all living cells to fuel biochemical reactions—makes use of a spinning molecular machine rather like Dr Feringa’s invention. This works rather well. The ATP generators in a human body turn out so much of the stuff that in a day they create almost a body-weight’s-worth of it. Do something similar commercially, and the hype might prove itself justified.