Researchers measure minuscule particles with 'tiny diving boards'

Researchers from MIT can now measure masses of particles as small as one millionth of a trillionth of a gram. 

The suspended nanochannel resonator (SNR), a high precision instrument devised by researchers, can determine the mass of particles with a resolution better than an attogram — one millionth of a trillionth of a gram, according to a press release by the Massachusetts Institute of Technology. 

With the help of the SNR, researchers can now determine the mass of minuscule-sized viruses, protein aggregates, and other naturally occurring and engineered nanoparticles (a nanometer is one-billionth of a meter), which were earlier difficult to measure due to their small size, according to the findings that were published in a paper for the Proceedings of the National Academy of Sciences. 

“Now we can weigh small viruses, extracellular vesicles, and most of the engineered nanoparticles that are being used for nanomedicine,” said Selim Olcum, one of the paper's lead authors. 

The SNR builds upon the suspended microchannel resonator (SMR), an earlier technology developed by Scott Manalis, an MIT professor of biological and mechanical engineering.

The SMR was used to track cell growth and measure density of cells, according to the MIT press release.

The SMR consists of a fluid-filled microchannel in a tiny silicon cantilever, a beam secured at one end. The particles are made to flow through the channel, one by one, and the mass of the particles changes the vibration frequency of the cantilever.

This frequency change helps to measure particle mass.

The SNR shares the same mechanism, too. But it was built by shrinking the size of the whole system, resulting in more than a 30-fold improvement over the SMR. To make the device sensitive to smaller masses, the researchers had to shrink the size of the cantilever, which behaves much like a diving board, Olcum said in the press release.  

“If you’re measuring nanoparticles with a large cantilever, it’s like having a huge diving board with a tiny fly on it. When the fly jumps off, you don’t notice any difference. That’s why we had to make very tiny diving boards,” Olcum said.

The efficient and speedy device can help the researchers measure almost 30,000 particles in a little more than 90 minutes, according to the press release.

“In the span of a second, we’ve got four or five particles going through, and we could potentially increase the concentration and have particles going through faster,” said Cermak, who is a co-lead author of the paper.