For the first time ever, physicists have developed a mechanical device that can measure the mass of individual molecules one at a time.
At just a couple millionths of a meter, the new tech will eventually help doctors diagnose diseases, enable biologists to study viruses and probe the molecular machinery of cells, and even allow scientists to better measure nanoparticles and air pollution, according to a Caltech news release.
The wee device consists of a tiny, vibrating bridge-like structure (pictured). When a particle or molecule lands on the bridge, its mass changes the oscillating frequency in a way that reveals how much the particle weighs.
Like a guitar string, a bridge can vibrate in distinct patterns of motion, or modes, each of which has its own distinct frequency. In the lowest frequency mode, the whole beam bows side to side. In the next higher-frequency mode, the two halves of the bridge bow in opposite directions while the point in the center remains stationary. In fact, the beam can vibrate in both of these modes at once. When a molecule sticks to the bridge, it will lower the frequency of both modes by different amounts. From those two frequency shifts, the scientists can deduce both the molecule's position on the beam and its mass.
The team, led by Calthech’s Michael Roukes, demonstrated how their new tool works by weighing a molecule called immunoglobulin M (IgM), an antibody produced by immune cells in the blood. By weighing each molecule, they were able to count and identify the various types of IgM. Future instruments could be used to monitor a patient's immune system or even diagnose immunological diseases. A certain ratio of IgM molecules is a signature of a type of cancer called Waldenström macroglobulinemia.
And generally, researchers could analyze a biological specimen to look for a telltale biomarker with a known mass, Scientific American explains.
The work was published in Nature Nanotechnology last week.
Image: Caltech / Scott Kelber and Michael Roukes