Researchers at Caltech, working with French colleagues, have figured out a mechanical means to weigh the previously un-weigh-able--things like individual molecules, viruses, proteins, and other particles--at the individual level, one by one. Such a scale should lead to huge leaps in understanding of molecular processes within biological cells, as well as advances in nanotechnology and other sciences of the very small.
The device, itself only a few millionths of a meter in size, taps the changes in an oscillating sensor to deduce the mass of individual particles that come in contact with it. Molecules or particles that land on this bridge-like structure alter the oscillation frequency of the sensor in ways that can be measured to determine exactly how much the particle weighs.
This technique isn’t wholly new. Molecules have been weighed previously via mass spectroscopy, where researchers take tens of millions of molecules and ionize them, then use an electromagnetic field to manipulate the newly charged particles in ways that reveal their masses. This works well enough for particles that readily hold charges, but for larger particles and especially those of a biological nature--pathogens, proteins, viruses--that don’t hold a charge well, mass spectroscopy is less than ideal.