Tiny scale weighs single molecules

Nature : The first device to measure the masses of individual molecules has been developed by researchers at Caltech and CEAâLeti, a government-funded research organization in Grenoble, France. Their nanoelectromechanical resonator uses a tiny silicon beam that vibrates at two different frequencies simultaneously, like a guitar string that vibrates at the fundamental and a harmonic. When a molecule sticks to the beam, it lowers the frequency of both modes by different amounts. Researchers can use the two frequency shifts to deduce the molecule’s position on the beam and its mass. The new technique could be ideal for studying molecules that are too heavy for traditional mass spectroscopy, which uses a magnetic field to bend the path of electrically charged molecules, and too light for electron microscopy, which uses a beam of electrons to illuminate a molecule and produce a magnified image.