A new subatomic weight scale can measure masses as tiny as one yoctogram. Less than the mass of a proton, a yoctogram is equivalent to a billionth of a billionth of a millionth of a gram.
A yoctogram is so tiny that it's effectively the endpoint of the metric system - there aren't any prefixes to describe units smaller than it. Until now, the most sensitive scales could only determine an object's mass to within 100 yoctograms. Admittedly, while 100 yoctograms is a perfectly decent margin of error for, well, everything we encounter in the world around us, at the atomic scale it's a bit like giving your weight to within the nearest ten tons.
All these ultra-tiny scales rely on nanotubes, which will vibrate at a specific frequency depending on the mass of the particles resting on them. As New Scientist reports, improving these nanotubes in turn allowed for the creation of even more sensitive scales:
To go even lower, Adrian Bachtold and his colleagues at the Catalan Institute of Nanotechnology in Barcelona, Spain, used short nanotubes. They give the best resolution and work at the low temperatures thought best for measuring frequency. Although the equipment was placed in a vacuum to minimise interference from other atoms, Bachtold removed any stray atoms by temporarily turning up the heat on the tubes to disrupt any bonds to atoms. Then the sensor was able to weigh an atom of xenon to the nearest yoctogram, or 10-24 grams. This makes it the first scale capable of detecting a single proton, which weighs in at 1.7 yoctograms.
Much as it might be fun to weigh oneself to the nearest proton, Bachtold says the main use of these scales will be in distinguishing nearly identical elements in chemical samples. There are also some potential medical applications, as certain molecular disease markers are only distinguishable at the proton scale.