Weighing Molecules And Viruses One By One Using Vibrations

Ever wonder how much a molecule exactly weighs? Sure we have atomic mass units which we can add up to get the weight of a molecule, but in order to actually weigh a molecule, scientists need to get creative. Now, a team of researchers from the California Institute of Technology (CalTech) have created a device that can measure the mass of individual molecules.

The device is essentially a tiny, vibrating bridge that measures only a few millionths of a meter. As particles pass through the device, they affect the oscillating frequency of the bridge, revealing the particles mass.

"As each particle comes in, we can measure its mass," says one of the authors of the paper, Michael Roukes, the Robert M. Abbey Professor of Physics, Applied Physics, and Bioengineering at Caltech. "Nobody's ever done this before."

Previously, Roukes and his colleagues had developed a similar bridge-like structure, a nanoelectromechanical system (NEMS) resonator, that could measure the mass of particles sprayed onto it. The only problem was that it depended on where these particles landed, so around 500 different measurements had to be taken in order to narrow in on the mass of a particle.

"The critical advance that we've made in this current work is that it now allows us to weigh molecules -- one by one -- as they come in," Roukes says.

The researchers hope that the device could have medical applications. For instance, scientists could measure nanoparticles in our bodies, as well as study incredibly miniscule structures such as viruses or cells.

Traditionally, a technique known as mass spectrometry is used to measure the masses of molecules. The problem with this method is that it does not fare well with larger particles like proteins and viruses. The technique developed by the CalTech team, on the other hand, has no problem with larger particles.

The scientists showed off their new device by measuring immunobglobulin M, an antibody. They were able to weigh and categorize different types of the molecules, which can take on different shapes and masses within the body. It is the first time that a biological molecule was weighed using a nanomechanical device, and provides promising evidence that the device could have useful medical applications.