Micro tweezers have ice grip

As the field of microscopic machines heats up, researchers are racing to find ways to manipulate minuscule objects.

Researchers from the Chinese Academy of Sciences have found that cooling things down makes for a simple way to rotate, twist, stretch, pick up and drop a wide range of microscopic items.

The researchers have constructed a freeze tweezer that uses the freezing force of a small volume of ice to manipulate objects suspended in a solution. Using a similar mechanism, they have made a simple electrical valve for microfluidic devices that closes by freezing a liquid and opens by thawing it.

The freeze tweezer uses high-pressure nitrogen gas running through a tiny coil to freeze liquid between a probe tip and an object, effectively gluing the tweezer and object together with a ball of ice. One or more freeze tweezers can be used to manipulate objects of any shape and electric charge, including biological objects, according to the researchers. The device can also be used to cool or heat groups of molecules.

The researchers' prototypes had tips as small as 20 microns, which is about one-quarter the width of a human hair. In theory, freeze tweezers could be made as small as several dozen nanometers, according to the researchers. A nanometer is one millionth of a millimeter.

The work appeared in the November 17, 2003 issue of the Journal of Micromechanics and Microengineering.