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Last Updated: Wednesday, 30 March, 2005, 22:28 GMT 23:28 UK
Scales tip with tiniest mass yet
Schematic of protein molecule, Brookhaven National Laboratory
Some hope devices could one day weigh biological molecules
US scientists have managed to measure the mass of a cluster of xenon atoms at just a few billionths of a trillionth of a gram - or a few zeptograms.

The record measurement is in the mass range of individual protein molecules, and the detection was made using sensitive scales developed at Caltech.

Similar techniques could pave the way for sensitive devices for use in medical and environmental testing.

Details were presented at the annual American Physical Society convention.

The scales use a small blade that vibrates in a magnetic field that generates a voltage in an attached wire.

When atoms or molecules are placed on the blade's surface, they weigh it down. The atoms are added as a very fine "spray".

Because the device is cooled, the molecules condense on the bar and add their mass to it, lowering its frequency and changing the voltage of the wire.

But to get good measurements of sophisticated biomolecules like proteins, researchers say, the scales will have to become 1,000 times more precise, capable of weighing yoctograms. One yoctogram is about the same as an individual hydrogen atom.

Devices like this could be used to make early diagnoses of disease by detecting marker molecules in a drop of blood.

"We hope to transform this chip-based technology into systems that are useful for picking out and identifying specific molecules one by one - for example, certain types of proteins secreted in the very early stages of cancer," said Michael Roukes, from the California Institute of Technology.

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