The world’s most sensitive scales can now detect a cluster of xenon atoms a billion, trillion times lighter than a gram.

A zeptogram (10-21)g) is roughly the mass of a single protein molecule and its detection has set a new record.



The feat opens up the prospect of future devices that could identify single molecules by weight, providing a sensor of extreme sensitivity that would be valuable in medical and environmental testing.



The key to the scales is a small blade that vibrates in a magnetic field, generating a voltage in an attached wire. When atoms or molecules are placed on its surface, they weigh it down, lower the vibration frequency and change the voltage.



In 2000, Michael Roukes and his colleagues at the California Institute of Technology in Pasadena, US, used a blade of silicon 10,000 nanometers long and 260 nanometres thick to weigh cluster of gold atoms with a mass of one attogram (10-18g).



But the Caltech team has now modified the device to make the scales a thousand times more precise. Making the vibrating blade from silicon carbide not silicon makes it stiffer and smaller – just 1000 nm long. It also increases its resonant frequency from 33 Megaherz to 190 MHz. That allows the detection of smaller masses placed on the blade. Roukes also improved the precision of the amplifiers and transducers that measure the voltage.



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