Machine Design
Microdevice can measure attograms

Microdevice can measure attograms

This illustration depicts a nanoparticle traveling over the cantilever in the microchannel of an SNR, where its mass is being measured with attogram resolution. The inset shows another particle, a gold-tagged DNA molecule from inside the channel as it passes through the resonator.

Engineers at the Massachusetts Institute of Technology (MIT) have improved a device they built that can measure particles in femtograms (10–15 gm) so it can now measure lighter particles in the range of attograms (10–18 gm) or a millionth of a trillionth of a gram.

The original device “weighed” particles in a fluid-filled microchannel etched in a silicon cantilever vibrating in a vacuum chamber. As a particle in a solution was sent through the microchannel, its mass altered the cantilever’s vibrational frequency. Engineers then calculate the mass of the particle based on that frequency change.

To boost the resolution to the attogram range, the team reduced the size of the cantilever so smaller particles will have a greater influence on its vibrational frequency. In their first version of the upgraded device (a suspended nanochamber resonator, or SNR), the cantilever was 50‑µm long, one-tenth the size of the cantilever in the femtogram SNR. The new version could measure particles as light as 77 attograms at a rate of 2/sec. The next SNR will have a cantilever 22.5‑µm long. It will also benefit from a new way to vibrate the cantilever, going from electrostatic excitation to piezoelectric. Piezoelectric excitation generates larger amplitude vibrations, which reduces the affect spurious vibrations (noise) have on the measurements. The upgraded SNR has been used to measure the mass of 30,000 particles in 90 min.

The SNR will be used to measure small viruses and biological features of cells, as well a engineering nanoparticles such as carbon nanotubes.

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