While on the macro-scale conventional scales make us of gravity to measure mass, on the microscale there are a myriad of factors that interfere with measurements. Scientists at Universitat Autònoma de Barcelona have successfully created a scale made out of a single carbon nanotube which can accurately measure the smallest unit of mass, a yoctogram (one septillionth of a gram – 10-24 grams) or the mass of a single proton. That’s 100 times less massive than previous experiments were able to determine.
This incredible sensitivity is made possible by measuring the difference in vibrational frequency. One single carbon nanotube approximately 150 nanometers (nm) long and 1.7 nm in diameter had both of its ends fixed, while at its center a one nanometer narrow trench was suspended. The nanotube has a resonant vibrational frequency of approximately 2 gigahertz (GHz), so when even the tiniest unit binds to its surface, it causes a change in resonant frequency, which is used to measure mass. Thus, the mass resolution they achieved is 1.7 yoctograms (1.7 × 10-24 grams) – the mass of a single proton.
To make the rig as accurate as possible, the operation was performed at about 6 degrees above absolute zero, to isolate it from thermal vibrations, and was placed in vacuum to minimise interference from other atom. Due to the extreme sensitivity of the nanotube resonator, the researchers were able to detect individual xenon atoms and naphthalene (C10H8) molecules which adhered to the surface of the nanotube resonator.
“The yoctogram mass sensitivity achieved by the Catalan team is certainly spectacular ‐ the challenge ahead will be to routinely manufacture nanotube sensors at low cost,” says Rachel McKendry, a nanoscientist at University College London.
The Spanish scientists’ device might pose a great potential for measuring very small masses, allowing for extremely high precision in mass spectroscopy, although subatomic particles are out of its range. Also, different elements in a sample, which might differ only by a few protons, could be distinguished by the carbon nanotube resonating scale.