Who are the founders of nanotechnology? It depends what you mean by nanotechnology, but a scientist's list of names would probably start with Richard Feynman, on the basis of his prescient lecture There's plenty of room at the bottom. Binnig and Rohrer would surely have an assured place for inventing scanning probe microscopy, and few could resist crediting Eigler for creating that iconic image of the letters ‘IBM’ in single atoms. Beyond that, the list rapidly grows rather long. But the name that would be missing from most scientists' list is the name that, in the minds of many in the general public, is most closely associated with nanotechnology – K. Eric Drexler.
Drexler was not the first to use the word ‘nanotechnology’. That distinction is usually given to the Japanese scientist Taniguchi, who coined the word in 1974. But Drexler, in his 1986 book Engines of Creation, certainly captured the public imagination and propelled nanotechnology into popular culture, inspiring the futuristic visions embodied in best-selling novels like The Diamond Age and Prey, and films like Spiderman andMinority Report. He envisioned intricate nanoscale machines, made from hard materials like diamond and using the principles of mechanical engineering. Most ominously, he anticipated autonomous, self-reproducing nanorobots leading the most apocalyptic prediction of all – that the ecosphere could be taken over by a plague of nanobots (the notorious ‘grey goo’).
Drexler has since dissociated himself from the idea of autonomous nanobots, but his reputation in the scientific community is at a very low ebb. The Drexlerian vision of nanotechnology has come under sustained attack from chemists such as Richard Smalley and George Whitesides, and my experience is that the private attitude of many prominent nanoscientists is even more vituperative than public debate suggests. Is there a danger that something may be lost in the hostilities; that, indeed, there may be something in what Drexler says?
Drexler's strongest argument is that the very existence of the amazing contrivances of cell biology shows that radical nanotechnology must be possible. “Biology shows that molecular machines can exist, can be programmed with genetic data, and can build more molecular machines”. This is clearly absolutely correct, and Drexler deserves credit for highlighting this important idea in Engines of Creation. But what happens if we pursue this argument a little further?
Cell biology shows that it is possible to make sophisticated molecular machines that can operate, in some cases, with atomic precision, and self-replicate. What it does not show is whether Drexler's approach to making molecular machines (“the principles of mechanical engineering applied to chemistry”) will work. The crucial point is that the molecular machines of biology work on very different principles to those used by our macroscopic products of mechanical engineering.
Drexler argues that we can do nanotechnology better than nature, because we can use hard, stiff materials like diamond, rather than the soft, wet and jelly-like components of living organisms, and that we can use the rationally designed products of a mechanical engineering approach rather than the ramshackle and jury-rigged contrivances of biology. But this underestimates the effectiveness of biological mechanisms at the nanoscale. Although biological design has obvious shortcomings at the macroscopic scale, the smaller we go, the better things work. A good example of this is the nanoscale machine adenosine triphosphate (ATP) synthase. This converts the chemical energy of a hydrogen ion gradient, first into mechanical energy of rotation, and then into chemical energy again, in the form of the energy molecular ATP (with an efficiency approaching 100%).
Biology works so well because it exploits unfamiliar physical phenomena that dominate on the nanoscale, using design principles completely unknown in the macroscopic world of mechanical engineering. These include self-assembly, in which strong surface forces and Brownian motion combine to allow complex structures to form spontaneously from their component parts. The lack of stiffness of biological molecules, and the importance of Brownian motion in continuously buffeting them, is exploited in the principle of molecular shape change as a mechanism for mechanical work in the molecular motors of our muscles. These biological nanomachines are exquisitely optimized for the nanoscale. Drexler's mechanical engineering approach treats phenomena like Brownian motion and strong surface forces as problems to be engineered around. But biology doesn't engineer around them; it finds ways of exploiting them.
Despite the opprobrium, Drexler has made an important contribution by drawing attention to the power of biological nanotechnology. At a time when some academic nanoscience is rather incremental, perhaps a lesson can be learnt from the sheer ambition of the Drexlerian vision. But I believe the main lesson is not that we will improve on biology by applying engineering principles. Rather, we will learn to do nanotechnology better by using biological principles.
[1] Richard Jones is professor of physics at the University of Sheffield, UK.