Canadian engineers have unveiled the creation of the world's smallest transistor in which electricity flows through a molecule.

The device is only visible through a powerful microscope, but experts say it may be the biggest development so far in nanotechnology, a science that aims to reduce computers and other devices to minuscule sizes.

"It's a big step forward. It could never have been said before with certainty that a molecule could be a building block and now there's no doubt," Robert Wolkow, head of the research team at the University of Alberta, said.

"It's no longer science fiction. There is no question, molecules can be used as electronic components."

The team's results appeared in the scientific journal Nature.

Typically, transistors are integrated circuits on silicon chips that act as the brains of electronic devices, regulating the flow of electricity. Transistors Mr Wolkow's gizmo, which consists of one to 20 molecules anchored to a silicon wafer, is nearly one thousand times smaller than conventional transistors and requires about one-millionth as much energy. Transistors An electrode or metal tip hovers above the molecule. When activated, "you can see a sloping effect, like a comet's tail," he said.

"You can see the decay of the electric field from the charge."

The breakthrough is the result of five years of work by Mr Wolkow and his colleagues.

That's how long the team took to figure out how to line up the molecules and the small electrodes and control the flow of electricity in repeated experiments at the National Institute for Nanotechnology in Edmonton.

But, consumers should not expect to see the technology in gadgets on store shelves anytime soon.

There are still many bugs to work out, Mr Wolkow said.

First, the metal probe that is "ever so carefully poised over the molecule" is moved into position using a special microscope that costs about $C1 million ($1.07 million).

Also, it takes the team several minutes to turn it on or off.

To be useful in a computer, it would need to make the switch in less than a microsecond, or one millionth of a second.

It is more likely the first applications for the device will be as a sensor or medical diagnostic tool that could trigger the release of drugs in specific locations in the human body or detect levels of iron or oxygen in the blood, Mr Wolkow said.