This week, a team of mechanical engineers set a new record for sensitivity: They announced that they can now measure forces as tiny as the weight of a single protein. Their device, unveiled at the American Physical Society meeting in Kansas City, Missouri, may lead the way to the development of an instrument capable of divining the shape of individual molecules.
The tiny scale consists of a single crystal of silicon, about a quarter of a millimeter long and about 60 nanometers thick, attached to its base like a diving board. The tip is covered with a thin coating of a magnetic cobalt-nickel alloy that vibrates when it encounters a weak magnetic field. By measuring the bobbing of the crystal with a laser, the device can detect forces as small as 36 attonewtons--an attonewton is about a billionth of a billionth of a kilogram. "It sets the world record for the smallest force directly measured," says Thomas Kenny, a mechanical engineer at Stanford University and one of the designers.
The sensitive instrument could become more than a curiosity, say the designers, who hope to use the technique to develop an even higher resolution magnetic resonance force microscope (MRFM), able to detect the tiny electromagnetic pulses that come from atoms' interaction with magnetic fields. Such a device could permit three-dimensional mapping of atoms within a molecule. "That would be a very important tool indeed," says team member Daniel Rugar, a physicist at IBM's Almaden Research Center.
Physicists and other scientists see no end to the applications. "You could use it to look at the biology of tumor cells, or the structure of cartilage," says John Sidles, a physicist at the University of Washington Medical Center who works on magnetic resonance. "Finding interesting things to study with MRFM would be like shooting fish in a barrel."