Have you ever wondered what a virus sounds like? Or what noise a bacterium makes when it moves between hosts? If the answer is yes, you may soon get your chance to find out, thanks to the development of the world’s tiniest ear. The “nano-ear,” a microscopic particle of gold trapped by a laser beam, can detect sound a million times fainter than the threshold for human hearing.
Looking at this from a completely scientific perspective, this is exciting news. But with the advent of new technology, sometimes there are downsides – like when the technology gets into the wrong hands.
It’s still at the experimental stage, but this could lead to far more sensitive surveillance microphones in the future. The required laser beam could be carried by a difficult-to-detect optical fiber strand to the sensor. Combined with DSP and advanced acoustic signal processing algorithms, this could represent a major security threat.
We already know that listening and viewing devices can be planted in homes and offices or people can carry audio listening devices on their clothing, etc. However, all of this requires a bit of work or being within a reasonable range of proximity to your target. Even then, the listening/recording quality may not be perfect. Can you imagine what a scary world this would be if people’s ears could be devised to be listening devices – not to mention with superb hearing capability? This sounds like some espionage Sci-Fi movie to me.
The concept of the nano-ear began with a 1986 invention known as optical tweezers. The tweezers use a laser beam focused to a point with a lens to grab hold of tiny particles and move them around. They’ve become a standard tool in molecular biology and nanotechnology, helping researchers inject DNA into cells and even manipulate it once inside. Optical tweezers can also be used to measure minuscule forces acting on microscopic particles; once you’ve grabbed hold of your particle with the laser beam, instead of moving it yourself, you simply use a microscope or other suitable monitoring apparatus to watch whether it moves of its own accord. That’s where the nano-ear comes in.
Sound waves travel as a forward and backward displacement of the particles of the medium they pass through. So to detect sound, you need to measure this back-and-forth motion.
As well as having unprecedented sensitivity, their nano-ear could also calculate the direction the sound had come from. They suggest three-dimensional arrays of nano-ears working together could be used to listen in on cells or microorganisms such as bacteria and viruses, all of which emit very faint acoustic vibrations as they move and respire.
Biophysicist Lene Oddershede of the Optical Tweezer Laboratory at the Niels Bohr Institute in Copenhagen is impressed and suspects the paper will inspire others in the field to look for sound waves when studying microorganisms. “It’s a really interesting idea, and we could easily do that, but we have never made any attempt to do so,” she says. “I would say this paper’s very inspiring in that sense.” She cautions, however, that the experimental setup will need to be significantly refined to improve its ability to separate sound waves from random molecular movement before the suggested acoustic microscope can become a reality. But she is optimistic: “I do believe they can relatively quickly improve the equipment.”
Read story@ sciencemag
