Imagine a world where microscopic medical implants patrol our arteries, diagnosing ailments and fighting disease; where military battle-suits deflect explosions; where computer chips are no bigger than specks of dust; and where clouds of miniature space probes transmit data from the atmospheres of Mars or Titan.
Many incredible claims have been made about the future's nanotechnological applications, but what exactly does nano mean, and why has controversy plagued this emerging technology?
Nanotechnology is science and engineering at the scale of atoms and molecules. It is the manipulation and use of materials and devices so tiny that nothing can be built any smaller.
How small is small?
Nanomaterials are typically between 0.1 and 100 nanometres (nm) in size - with 1 nm being equivalent to one billionth of a metre (10-9 m).
This is the scale at which the basic functions of the biological world operate - and materials of this size display unusual physical and chemical properties. These profoundly different properties are due to an increase in surface area compared to volume as particles get smaller - and also the grip of weird quantum effects at the atomic scale.
If 1 nanometre was roughly the width of a pinhead, then 1 metre on this scale would stretch the entire distance from Washington, DC to Atlanta - around 1000 kilometres. But a pinhead is actually one million nanometres wide. Most atoms are 0.1 to 0.2 nm wide, strands of DNA around 2 nm wide, red blood cells are around 7000 nm in diameter, while human hairs are typically 80,000 nm across.
Unwittingly, people have made use of some unusual properties of materials at the nanoscale for centuries. Tiny particles of gold for example, can appear red or green - a property that has been used to colour stained glass windows for over 1000 years.
Nanotechnology is found elsewhere today in products ranging from nanometre-thick films on "self-cleaning" windows to pigments in sunscreens and lipsticks.
Nano is born
The idea of nanotechnology was born in 1959 when physicist Richard Feynman gave a lecture exploring the idea of building things at the atomic and molecular scale. He imagined the entire Encyclopaedia Britannica written on the head of a pin.
However, experimental nanotechnology did not come into its own until 1981, when IBM scientists in Zurich, Switzerland, built the first scanning tunnelling microscope (STM). This allows us to see single atoms by scanning a tiny probe over the surface of a silicon crystal. In 1990, IBM scientists discovered how to use an STM to move single xenon atoms around on a nickel surface - in an iconic experiment, with an inspired eye for marketing, they moved 35 atoms to spell out "IBM".
Further techniques have since been developed to capture images at the atomic scale, these include the atomic force microscope (AFM), magnetic resonance imaging (MRI) and the even a kind of modified light microscope.
Other significant advances were made in 1985, when chemists discovered how to create a soccer-ball-shaped molecule of 60 carbon atoms, which they called buckminsterfullerene (also known as C60 or buckyballs). And in 1991, tiny, super-strong rolls of carbon atoms known as carbon nanotubes were created. These are six times lighter, yet 100 times stronger than steel.
Both materials have important applications as nanoscale building blocks. Nanotubes have been made into fibres, long threads and fabrics, and used to create tough plastics, computer chips, toxic gas detectors, and numerous other novel materials. The far future might even see the unique properties of nanotubes harnessed to build a space elevator.
More recently, scientists working on the nanoscale have created a multitude of other nanoscale components and devices, including:
Tiny transistors, superconducting quantum dots, nanodiodes, nanosensors, molecular pistons, supercapacitors, "biomolecular" motors, chemical motors, a nano train set, nanoscale elevators, a DNA nanowalking robot, nanothermometers, nano containers, the beginnings of a miniature chemistry set, nano-Velcro, nanotweezers, nano weighing scales, a nano abacus, a nano guitar, a nanoscale fountain pen, and even a nanosized soldering iron.
Engineering wonder
Engineering at the nanoscale is no simple feat, and scientists are having to come up with completely different solutions to build from the "bottom-up" rather than using traditional "top-down" manufacturing techniques.
Some nanomaterials, such as nanowires and other simple devices have been shown to assemble themselves given the right conditions, and other experiments at larger scales are striving to demonstrate the principles of self-assembly. Microelectronic devices might be persuaded to grow from the ground-up, rather like trees.
Researchers are also finding ways to put proteins, DNA, viruses and bacteria and other micro-organisms to work in building nanomaterials, and also taking other inspiration from the natural world.
Some problems have arisen due to a lack of consistency in measuring distances at the nanoscale, but an atomic lattice nanoruler could improve accuracy.
Diminutive debate
Despite the fact that it still has relatively few commercial applications, nanotechnology has generated criticism from environmental groups and others - such as the UK's Prince Charles - who fear as-yet-unknown risks to human health and the environment.
Critics have called for a moratorium on research, arguing that we know little about the toxicological effects of nanoparticles, and that there are no regulations to control them - nanotechnology advocates simply call this scaremongering, and fail to understand what all the fuss is about.
Futurist K Eric Drexler - credited with coining the term nanotechnology - dreamed up one possible nightmare scenario in his1986 book Engines of Creation. Though he now deems it an unlikely scenario, Drexler stirred fears about nanotechnology by painting a future where tiny, self-replicating nanobots run amok, digesting life on earth and reducing everything to a "grey goo".
The few experimental studies to date into the health impact of nanoparticles reveal that high concentrations of nanotubes could damage the lungs of rats and mice. One 2004 study hinted that buckyballs can accumulate and cause brain damage in fish.
A report, independently commissioned in 2003 by the environmental group Greenpeace, acknowledged that - while there could be risks from nanotechnology - the field could generate significant innovations to benefit the environment. A 2004 report, commissioned by the UK government, argued that most nanotechnology presents few novel risks, but recommended more research, along with new regulations to control the technology.
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