Some of the smallest solar cells ever made have been successfully tested as a power source for even tinier microscopic machines.

Each cell is just over 1mm long - that's about a quarter the size of a lowercase 'o' in a standard 12-point font.

Unlike bulky, brittle silicon solar panels, the new cells are made from an organic polymer that can be dissolved and printed on to a flexible material.

Anyone for electricity-generating sun block?

According to Xiaomei Jiang, who led the research at the University of South Florida: "They could be sprayed on any surface that is exposed to sunlight -- a uniform, a car, a house."

Jiang and her colleagues fabricated an array of 20 tiny photovoltaic cells for use as a power source for a tiny device, in this case a carbon nanotube sensor for dangerous chemicals and toxins.

Currently, the array can supply nearly 8V of electricity, although Jiang hopes to double that as soon as the end of this year.