Scientists have made a pair of tweezers capable of picking up objects just 500 nanometres (billionths of a metre) across.

The achievement is being hailed as another milestone in the fast-developing field of nanotechnology in which researchers manipulate matter at the scale of individual atoms and molecules.

The nanotweezers could become an important part of the toolkit that one day allows us to create a host of molecular-scale devices with extremely miniaturised electronic circuitry.

It might even allow biologists to manipulate the minute structures within cells.

Dr Philip Kim and Professor Charles Lieber made their microscopic gadget from two carbon nanotubes - tough but tiny cylinders of carbon atoms which are just four microns (millionths of a metre) long and 50 nanometres in diameter.

The carbon tubes were attached to gold electrodes either side of a glass rod. And by applying a voltage to the device to exploit the electrical properties of the tubes, they were able to make the arms open and close - just like the arms on a normal pair of tweezers.

Plastic beads

The University of California-Berkeley and Harvard researchers have demonstrated the dexterity of their nanotool by grabbing, dragging, shoving and poking clusters of plastic beads which measured less than 500 nanometres across.

"We were also able to grab a gallium arsenide wire that was only 20 nanometres in diameter," Professor Lieber told BBC News Online.

The tweezers could have been made smaller but the researchers wanted to demonstrate the principle at a size that could be picked up by an optical microscope.

Because the nanotube arms can conduct electricity, they were also used to probe the electrical properties of other clusters and nanoscale wires in their grasp. The researchers now expect to make their tweezers even smaller.

"We wanted to create a tool that would allow us to manipulate nanoscale matter in three dimensions," Professor Lieber said. "Whether you are thinking about nanotechnology from an electrical, optical or a biological standpoint, you need to assemble and manipulate things in three dimensions and not only in 2D or in a plane which is what most of the tools in our current box of tricks can do - the scanning probe microscopes."

Big future

Chad Mirkin, of Northwestern University, Illinois, who is credited with making the world's smallest pen, has welcomed the development of the nanotweezers.

Professor Mirkin says that scientists need to find nano equivalents to many of the construction tools we use in the larger world.

If researchers can do that, he believes, "all signs point to [nanotechnology] as one of the biggest growth areas in science and engineering for the next quarter century".

This is why, he says, Kim and Lieber's work is an important development.

He thinks the device will become an important analytical tool and could lead to improvements in the very powerful microscopes that can now image and probe individual atoms.

"Many other applications for the nanotweezers are within the realm of possibility, including its use in manipulating biological structures on surfaces or even within cells."

Professor Lieber's goup is now developing the nanotweezers for use in the fabrication of tiny electronic devices and for imaging and manipulating biological samples.

The nanotweezer research and Professor Mirkin's commentary are published in the journal Science.