Scientists have devised a nanotube-based mechanical sensor for weighing molecules, reports a paper online in Nature Nanotechnology this week. Unlike many existing mass spectrometers, the new device would not damage the molecules it is measuring. The authors test their new sensor by weighing a single atom of gold.
A gold atom has a mass of 3.25 x 10?25 kilograms, which means that there are about 3 million million million million gold atoms in a kilogram. The double-walled carbon nanotube used by Kenneth Jensen and co-workers is about 7,000 times heavier than a gold atom and measures just 2 nanometres across and 254 nanometres in length.
The nanotube is attached to an electrode at one end, leaving the other end free to vibrate like an extremely small diving board. When an atom or some object lands on the nanotube, the natural vibration frequency changes by an amount proportional to the mass of the object, enabling it to be weighed.