A gold particle five nanometers in width weighs just a few megadaltons, a tiny unit of measure used in biochemistry that is equivalent to the atomic mass unit. However, researchers at the California Institute of Technology and CEA-Leti, a government-funded research organization in Grenoble, France, have built a scale that weighs single objects, including nano-particles and human antibody molecules. It’s the first device of its kind that can be used to determine the masses of individual molecules.
The scientists published their findings in the journal Nature Nanotechnology. The device is run by a nanoelectromechanical resonator, a tiny beam of silicon vibrating two tones simultaneously. It’s continually being subjected to electrostatic excitation. The beam runs diagonally and measures 10 microns long by 300 nanometers wide. Tiny arms connect the ends of the beam to the rest of the device, where the resonator’s vibrations are converted into an electrical signal using a phenomenon known as the piezoresistive effect. When a single molecule lands on the beam, it shifts the frequency of the two tones downward. This allows researchers to deduce the mass of the particle.
The sensitivity of the device has allowed scientists to perform mass spectroscopy, which helps identify the various particles in a mixture by their masses, on collections of gold nano-particles.
Past resonators were only able to measure molecular masses after hundreds of identical molecules had been deposited onto the beam. The new more sensitive device allows researchers to perform mass spectroscopy to identify the various individual particles within a mixed sample.
Reference: “Single-protein nanomechanical mass spectrometry in real time” by M. S. Hanay, S. Kelber, A. K. Naik, D. Chi, S. Hentz, E. C. Bullard, E. Colinet, L. Duraffourg and M. L. Roukes, 26 August 2012, Nature Nanotechnology.