A miniature stethoscope 100 times thinner than a human hair could be used to detect tiny changes in cells, including signals that they might be becoming cancerous.
The nano-sized device is an optical fibre that's sensitive enough to detect forces from bacteria and sounds from heart muscle cells. These are forces as tiny as 160 femtonewtons – about as much force as six red blood cells would exert on your palm – and sounds as quiet as -30 decibels, which is 1,000 times quieter than the human ear can detect.
The device, developed by engineers at the University of California, San Diego, is a fibre of tin dioxide surrounded by the polymer polyethylene glycol, which is studded with gold nanoparticles. The whole thing is only a few hundred nanometres in diameter.
Donald Sirbuly, the nanoengineering professor who led the study, says that the work could open up new ways to track tiny interactions and changes in the body. This could include detecting the presence of a single bacterium, monitoring a cell's acoustics, or even sensing changes in a cell which might mean it is becoming cancerous or being attacked by a virus.
To test the device, the fibre was placed in solutions containing either live Helicobacter pylori bacteria or beating heart muscle cells. Their movements compressed the polymer layer and caused changes in the intensity of the light signals traveling down the optical fibre, which were then scattered by the gold nanoparticles and detected by a conventional microscope.
What makes this device special is that the small forces and sounds cannot just be detected, but quantified, allowing high resolution images. So perhaps doctors will soon be carrying around a second stethoscope – one that's invisible to the naked eye.