Researchers at the Oak Ridge National Labs in Tennessee have claimed a new world record for weighing tiny amounts of stuff. Tiny gold-coated silicon bars two microns long and fifty nanometres thick were vibrated by heating them with a solid-state laser at around two million times a second, and variations in their resonant frequency measured.
Those variations reflected extra weight loaded onto the bars -- in this case, masses as low as 5.5 femtograms could be detected. A femtogram is one billion billionth of a gram, or roughly the mass of 122 gold atoms.
By coating the bars with different substances, they can be made to absorb particles of different natures -- DNA, proteins, cells or trace amounts of chemical contaminants. This is the basis of an exceptionally sensitive detector for airborne substances: researcher Panos Datskos expects the technology to be able to detect single molecules in the near future, once the vibration frequency is raised to 50 MHz by fabricating smaller, stiffer bars.
"We can control very precisely the effect of the laser, and not only did we detect this small mass, but we did so under ambient conditions. People can probably do this very easily in a vacuum, but to do it in air and in the presence of friction because the cantilevers have to displace air to vibrate so friction increases -- people have had great difficultly so far trying to achieve that," Datskos told industry publication EE Times.
He also said that his team was working on a 'universal' device that could detect any substance by an array of ten different lengths of sensor, and that would be hand-held. Power consumption would be very low: the most energy-demanding part of the device, the laser, is the same kind as used in portable CD players.