Putting Particles on a Scale
Scales have been an invaluable tool for ages as they regulated commerce and helped us track diets. Bathroom scales and balances are not always the proper instrument to use though, so when you want to weigh something special, you need a special balance. Researchers at MIT have recently built a pretty special balance with a resolution of less than an attogram (0.000000000000000001 grams).
This new scale is meant for weighing particles such as the nanoparticles used in medicine and viruses. It operates similarly to a scale developed in 2007 by an MIT professor. The particles flow through a microscale channel on a cantilever that vibrates. As the particles travel along the cantilever, the frequency of the vibration changes predictably. To achieve the 0.85 attogram resolution this new scale has, the researchers had to shrink the design, making the cantilever 22.5 microns long with the channel being one micron wide and four hundred nanometers deep. The smaller the cantilever the higher the frequency it can vibrate at, making it more responsive to small masses.
The researchers are currently investigating applying this device to measure certain particles in the blood of some cancer patients. Some tumors produce a large number of particles called exosomes, and tracking their concentration could be useful when a patient is being treated.