Washington, Some of the tiniest solar cells built to date have been successfully tested as a power source for even tinier machines.

They have been described as an inch-long array of 20 of these cells -- each one about a quarter the size of a lowercase 'o' in a 12-point font.

Xiaomei Jiang of University of South Florida, who led the research and her colleagues fabricated their array of 20 tiny solar cells as a power source for running a microscopic sensor for detecting dangerous chemicals and toxins.

Traditional solar cells use a brittle backing made of silicon, the same sort of material upon which computer chips are built. By contrast, organic solar cells rely upon a polymer that has the same electrical properties of silicon wafers but can be dissolved and printed onto flexible material.

"I think these materials have a lot more potential than traditional silicon," said Jiang. "They could be sprayed on any surface that is exposed to sunlight -- a uniform, a car, a house," Jing said.

The detector, known as a microeletromechanical system (MEMS) device, is built with carbon nanotubes and has already been tested using ordinary DC power supplied by batteries, said a release of South Florida.

When fully powered and hooked into a circuit, the carbon nanotubes can sensitively detect particular chemicals by measuring the electrical changes that occur when chemicals enter the tubes. The type of chemical can be distinguished by the exact change in the electrical signal.

The device needs a 15-volt power source to work and Jiang's solar cell array can provide about half of that -- up to 7.8 volts in their lab tests. The next step, she said, is to optimise the device to increase the voltage and then combine the miniature solar array to the carbon nanotube chemical sensors.

The new technology has been described in the inaugural issue of the Journal of Renewable and Sustainable Energy.

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