In the physics department at the Indian Institute of Science there is a diagram on the wall which is not the usual tangle of forbiddingly complex equations. It shows tap water running over a honeycombed surface of a tube attached to a voltmetre; does water running over this tube generate electricity?
"In principle it’s true," says Professor Ajay Sood, whose discovery the diagram represents. Sood and his student Shankar Ghosh have shown that bundles of single-walled carbon nanotubes placed in a flowing liquid generates electricity. Nanotubes are microscopic. That’s why Sood adds, "There is just one problem with that diagram. It’s not to scale."
Nanotubes were discovered in 1991 by Japanese scientist Sumio Iijima. They have found various audacious applications today, including a daring dream of bundling them to create a strong but light rope that will take elevators into space.
A single-walled nanotube is a layer of carbon molecules folded like a tube. Sood’s experiments proved that the flow of a liquid over a nanotube pushes electrons down it in a single direction, generating electricity. While the applications in power generation are a theoretical possibility, what excites Sood the most is the use of these minuscule nanotubes as sensors "with unimaginable sensitivity", able to detect "the slightest of slightest disturbance over a very large area". It will radically change the world of sensors. The applications in military’s stealth operations are as big as one’s fertile imagination. The microscopic size of the nanotube sensors also makes it possible for them to investigate the human body at an extraordinarily minute level. The sensors could also probe deep into the world of microbes. "Can’t say anything more at this stage," says Sood. "It’s confidential."