010816-16 10.1038/nsu010816-16 16 August 2001 technology Bull wins size prize John Whitfield technology nanotechnologytwo-photon polymerization Medicine and computers could benefit from nano sculpture.

The smallest bull in the world: red lines equal to 2 millionths of a meter© S. Kawata et al.

This bull is the size of a red blood cell. Its Japanese creators hope that the technology they used to make it will find applications in computing and medicine.

Satoshi Katawa and colleagues at Osaka University used two laser beams to sculpt the micro-beast from resin, which solidifies only where the lasers cross. The team refined this 'two-photon micropolymerization' to a resolution of 120 nanometres (120 billionths of a meter).

They chose a bull, says team member Hong-Bo Sun, because it has a "very sophisticated three-dimensional shape with sharp tips and a smooth and rough body".

"We dream that this bull pulls a drug cart through the blood vessels," says Sun, suggesting that similar-sized micromachines could one day travel, Fantastic Voyage-style, around the body to treat disease. The technique could also be used to make microscopic sensors, templates for cell cultures and three-dimensional computer memories.

The technology is still in its early days, however. The time needed to build structures pixel-by-pixel could be a problem, says chemist Bob Denning of the University of Oxford. But the resolution of the sculptures is "remarkable - it'll be very tough to get better," he says.

Kawata, S., Sun, H.-B., Tanaka, T. & Takada, K. Finer features for functional microdevices. Nature 412, 697 - 698 (2001). Wet where you want22March2000Microsculpture made easy2March2000Nanotechnologyfig from paper