“But now I can take a speck of nothing and park it next to a nerve or organ, your [gastro-intestinal] tract or a muscle, and read out the data.”
Ultrasound vibrations, which can penetrate almost every part of the body, are used to power the sensors, which are about a millimetre across.
They contain a special crystal that converts ultrasound into electricity to power a tiny transistor.
If there is a voltage spike in a nerve or muscle fibre this alters the vibration of the crystal, changing the way the sound echoes back to an ultrasound receiver.
So far, experiments have been carried out on muscles and the peripheral nervous system of rats, but the researchers believe the dust could also work in the central nervous system and brain to control prosthetics.
This can already be done using brain implants, but these require wires that go through a hole in the skull, potentially allowing in infection or movement of the sensor within the brain. They must also be replaced after about one to two years.
The researchers are currently building neural dust that could last in the body for more than 10 years. And because they are wireless there is no need for holes to remain in the skull.
Professor Jose Carmena, a neuroscientist at Berkeley, said: “The technology is not really there yet to get to the 50-micron target size which we would need for the brain and central nervous system.
“Once it’s clinically proven, however, neural dust will just replace wire electrodes. This time, once you close up the brain, you’re done.”
However he added: “The beauty is that now, the sensors are small enough to have a good application in the peripheral nervous system, for bladder control or appetite suppression, for example.”