GREY GOO is dead - by royal decree. The idea that the world will be reduced to an amorphous mess by an army of self-replicating nanobots belongs "in the realms of science fiction", says Prince Charles, heir to the British throne. Writing in The Independent on Sunday newspaper, he denies that he ever believed the grey goo scenario. Nevertheless, the royal brow is still furrowed over nanotechnology's risks.

It would be easy to dismiss the prince's concerns: he holds eccentric views. He has enraged doctors by advocating alternative medicines and infuriated the biotech industry by opposing genetically modified foods. Even on nanotechnology, he is extreme: he endorses the notion that nanotechnology could lead to a repeat of the thalidomide disaster.

But his fears over nanoparticles, one branch of nanotech, are not so outlandish. The small scale of these specks endows them with unique properties which, as New Scientist has argued ...