Almost 40 years ago, Raquel Welch and Stephen Boyd climbed into a submarine, armed to the teeth, and began Hollywood's celebrated Fantastic Voyage. Once military boffins had shrunk both vessel and crew to microscopic size, the intrepid team set out on a search-and-destroy cruise through the human body. Their mission: to find and remove a blood clot in the brain of a top scientist, which had kept him in a coma following an assassination attempt. The result: classic Sixties science fiction.
Ms Welch and her modern successors may still be a long way from taking a tour of anybody's innards, but a sort of fantastic voyage is unlikely to remain science fiction for long. Scientists have long been intrigued by the prospect of designing miniature submarine-like capsules that could swim through the bloodstream, diagnosing disease and targeting more precisely than ever the rogue cells and pathogens that cause it. Now, advances in the burgeoning field of nanotechnology are promising to turn that prospect into reality.
Nanotechnology is one of the buzz-words of modern science but, in truth, it is a fancy phrase for something that common-or-garden chemists have been doing for centuries: manipulating matter at ever-smaller scales. Chemists, indeed, sometimes get rather upset that an aspect of their discipline has been given a catchy new title, accusing physicists of "muscling in". And as Sir Harry Kroto, a British Nobel chemistry laureate and one of the pioneers of the field, puts it, the term is actually meaningless: the prefix nano-, which comes from the ancient Greek for "dwarf", means the following unit should be divided by a billion as in nanometre. "Technology" doesn't quite work that way.
What nanotechnology involves is working with atoms and molecules on a nanometre scale. It can be hard to conceive quite how small this gets. A nanometre is a billionth of a metre, or a millionth of a millimetre. You would get about 50,000 of them across the diameter of the finest human hair. It is hard to go any tinier, before reaching the realm of sub-atomic particles: even the smallest atoms are a tenth of a nanometre across.
Small, however, is certainly beautiful. All matter is constructed from atoms, and manufacturing anything at all involves rearranging them. Modern ways of doing this might look sophisticated to our eyes, but they are pretty crude at a molecular level. "Casting, grinding, milling and even lithography move atoms in great, thundering, statistical herds," says Christine Peterson, president of the Foresight Institute in the US. "It's like trying to make things out of Lego blocks with boxing gloves on your hands. Yes, you can push the Lego blocks into great heaps and pile them up, but you can't really snap them together the way you'd like."
Learn to move the Lego blocks precisely, however, and some interesting possibilities start to emerge. "In the future, nanotechnology will let us take off the boxing gloves," Dr Peterson says. "We'll be able to snap together the fundamental building blocks of nature easily, inexpensively and in most of the ways permitted by the laws of physics." In short, scientists will be able to build materials and machines from the bottom up, putting every atom into the precise position where it will do most good.
This is done by molecular robotic devices that precisely position molecular components. The process is known as "positional control".
In an influential 1959 lecture, entitled "There's Plenty of Room at the Bottom", the great Nobel prize-winning physicist Richard Feynman said: "The principles of physics, as far as I can see, do not speak against the possibility of manoeuvring things atom by atom." Now, scientists are starting to do just that. The first exciting implication of this is the prospect of putting together your own molecules. Both the graphite in your pencil and diamond are made of carbon; the vast difference in strength between the two comes from the pattern of the molecular bonds. Try out different ways of sticking atoms together, and you'll eventually end up with new materials with extremely valuable properties. Early work in this field is already producing some extremely useful results. In 1991, the Japanese scientist Sumio Iijima discovered a new cylindrical carbon structure with remarkable physical, chemical and electrical properties.
Known as nanotubes, these rolled-up cylinders of carbon are already being used in scores of engineering and high-performance electronics applications. Carbon nanotubes have a tensile strength 100 times stronger than steel, yet they are half as dense as aluminium. Depending on details of their structure, they can be conductors or semi-conductors of electricity, making them extremely valuable components for electronics. One company has already made use of their strength in a lightweight but highly powerful tennis racket, and the world nanotube market is expected to top $400 million next year.
The development of nanotubes has even made plausible one of Arthur C Clarke's great visions of the future: permanent elevators to space, to lift satellites, spacecraft and even space tourists into orbit. The idea, expounded in Clarke's 1979 novel Fountains of Paradise, has always been considered impossible for want of a material strong yet light enough for cables that would have to stretch tens of thousands of kilometres high.
Scientists, however, think nanotubes could well be the answer. Last month, a Nasa conference in Santa Fe, New Mexico, gave serious consideration to how it could be done. Though no one has yet made a cable from nanotubes, the technical possibility is certainly there.
More exciting even than these new materials is the prospect of miniature machines. Follow Feynman's principles, and one can not only build molecules but join them together to create tiny devices on a scale that was recently unimaginable. In August, a team led by Professor David Leigh of the University of Edinburgh announced they had built a rotating molecular motor about a billion times smaller than that of the typical car. Light of different wavelengths breaks the molecular bonds that hold rings of atoms together, prompting rotational motion. The result is a miniscule dynamo that could be fitted, for example, to nanoscale capsules filled with drugs to transport them around the body.
Other scientists are concentrating on building nanoscale computers. A team from Cornell University in New York state last year created the first transistor - the on-off switch that is the most basic component of electronic circuits - from a single cobalt atom, attached to two gold atoms that work as electrodes. At one nanometre across, it is more than 100 times smaller than the tiniest components available before. Another team, at Harvard University, achieved similar results using two atoms of vanadium.
If these transistors can be built into chips and circuits - and there is no reason why they should not be - scientists will soon be able to compress the processing power of a modern laptop into a circuit board no larger than the full stop at the end of this sentence. Then the possibilities are endless - at both ends of the size scale. Nanoscale computing will bring us PCs with the power of a large company's mainframe, with a similar boost in that mainframe's capacities. The applications of tiny computers are, if anything, even more exciting. Microprocessors made from a small cluster of molecules can be added to all sorts of materials to make them "smart".
Today, our mobile phones, cookers and fridges carry microchips. Tomorrow, the same could become true of the fabric of our clothes, and the metal we turn into cars, cables and girders. Imagine a plastic food wrapper that knows when the contents are putrid, and changes colour to advertise the fact. Or a steel joist that informs an engineer when the strain it is bearing starts to get dangerous, or an artificial knee joint that can tell when it is infected. These developments are no longer science fiction.
Neither, once you put these applications together, is the Fantastic Voyage - though it will have to embark without Raquel Welch. Put a molecular motor on a nanoscale capsule, and you have a medical submarine quite small enough to swim through the bloodstream. Fill it with drugs, and add a molecular computer to take care of navigation and fire control, and you have the hunter-killer model that can seek out cancer cells or pathogens, before releasing its lethal payload. The advantages would be huge: chemotherapy drugs, for example, could target tumours with incredible precision, limiting the damage to healthy tissue which causes devastating side effects.
Though it has already chalked up some major accomplishments, and rests squarely within the framework of modern chemistry, nanotechnology is a field in its infancy, with its greatest potential still decades away. But with the correct investment, it has the power to change the face of medicine, engineering and electronics for the better. It is the ultimate in thinking small to act big - allowing us to make things from the bottom up, rather than the top down. The more precisely we learn to move and exploit atoms, the wider the range of uses to which they can be put. This means, as the Foresight Institute puts it, "better, faster, stronger, smaller and cheaper systems".
Tony Blair describes the field as "startling in its potential", promising to "create whole new industries and products we can't begin to imagine."
His Science Minister, Lord Sainsbury of Turville, agrees, noting its potential to bring "huge benefits for the environment and our health and wealth". Science magazine, one of the world's leading scientific journals, has named the advance of nanotechnology as one of the great breakthroughs of the 21st century so far. It would be foolish to bet against the same verdict being reached at the century's end.
Mark Henderson is the science correspondent at The Times
COSMETICS: Nanoparticles of titanium dioxide are used in some sunscreens, as at this scale molecules of the compound are transparent to normal light but reflect harmful ultraviolet rays. Nanoparticles are also used in several face creams, as their tiny size allows beneficial chemicals to penetrate the skin more readily. Amore Pacific, a Korean cosmetics company, uses nanoparticles of silver in underarm deodorant products. Silver is an antimicrobial agent, which kills the bacteria that form unpleasant body odours.
TENNIS RACKETS: Babolat, a French company, has marketed the first range of tennis rackets strengthened with carbon nanotubes. The nanotube fibres combine great strength and lightness, allowing players to hit the ball with more power.
DENTAL FILLINGS: Several companies are using nanoscale particles in dental fillings. Altair Nanotechnologies, for example, produces nanosized zirconium oxide for use in fillings. Rudi Moerck, the company's president, says: "(The material) is ideal for dental applications because of its strength and transparency to light, but it is opaque to X-rays, making it an excellent material for UV-cured dental fillings."
MEDICAL DRESSINGS: Nanoparticles of silver,a powerful antibacterial agent, have been impregnated in wound dressings to fight infection. Scientists in South Korea are also investigating ways adding the particles to socks, to guard against malodorous feet.
RESISTANT FABRICS: The North Carolina company Nano-Tex LLC sells stain-and wrinkle-resistant fabrics that are used in Levi Dockers and Lee Jeans trousers. Nanoparticles of a proprietary chemical penetrate the fabric deeply, and repel foreign substances that would otherwise stain.
SELF-CLEANING GLASS: Pilkington last year launched Activ glass, which has a coating only 40 nanometres thick to keep it clean. The coating uses nanoparticles of titanium dioxide and a photocatalyst that reacts with ultraviolet rays to break down organic debris. The coating also prevents rainwater from forming droplets, thus washing dirt away
NANOBOTS AND THE FEAR OF THE GREY GOO...
Not everyone is yet as enthusiastic about nanotechnology as the experts.
Many accept its potential to transform electronics, medicine and other fields, but some fear it could do more harm than good. The critics, primarily from environmental groups that are sceptical about modern technologies, are concerned about the possible creation of tiny, self-replicating nano-machines, which, they argue, could spread beyond the control of scientists in terrifying ways.
"Nanobots" with the ability to make copies of themselves, by removing the requisite molecules from other forms of matter, could rapidly turn the world into an ugly mass of "grey goo", the doomsayers predict.
Dr K Eric Drexler, of the US-based Foresight Institute, has this sombre warning:"If the first replicator could assemble a copy of itself in 1,000 seconds, the two replicators could then build two more in the next 1,000 seconds. In less than a day, they would weigh a tonne, in less than two days they would outweigh the Earth, in another four hours, they would exceed the mass of the Sun and all the planets combined."
This sounds like science fiction, because that is what it is: the nightmare scenario was floated by Michael Crichton, the author of Jurassic Park, in his recent novel Prey.
The idea has been picked up by campaigners, among them the Prince of Wales.
Organisations such as Greenpeace, the Green Party and the ETC Group argue that the risks are huge and should be considered more carefully.
Caroline Lucas, of the Green Party, says: "No one knows the long-term effects of manipulating matter at the atomic level." She wants a moratorium on any commercial use of the technology, until a strict regulatory framework is in place.
The most outlandish concerns are dismissed by those working in the field.
As Sir Harry Kroto points out, nanotechnology is essentially chemistry with a new name, and scientists do understand remarkably well how moving atoms about affects them. That is what chemistry is about, and Ms Lucas's claims, he says, are nonsense.
The "grey goo" dystopia is seen by most researchers as nothing more than scaremongering. Sir Harry and another British Nobel chemistry laureate, Sir Aaron Klug, were openly derisive of Prince Charles when he raised his worries about the subject.
Sir Harry remarked: "It shows a complete disconnection from reality."
Self-replicating robots on a nanometre scale might make a good plot for a sci-fi thriller, but they are so far from reality as to be preposterous.
Sir Harry notes: "Machines that can self-replicate are mosquitoes, and they are 100 million times bigger than a nanometre. The closest we are to fabricating mosquitoes are helicopters - and when two helicopters come together, they don't exactly self-replicate."
Grey goo might be too far-fetched to worry about, but what about other potential risks? All scientists accept that new technology can usually be employed for good or for ill, and nanotechnology is no exception. The Royal Society and the Royal Academy of Engineering has set up an inquiry to investigate the risks, chaired by Professor Ann Dowling of Cambridge University.
One matter that might be worth worrying about is the safety of nanoparticles. At very small scales, the properties of some materials change, and there are concerns that this could cause novel toxicity problems. A substance that is harmless in larger particles may be carcinogenic or poisonous in nanoparticle form, and Professor Dowling's inquiry aims to address this.
"The air is already full of nanoparticles both naturally occurring and man-made - indeed everyday incidents like burning a piece of toast add to them," she said.
"The study will explore whether nanoparticles produced by new technology have the potential to cause additional risks."