Last week in the London Student Science section I wrote about the record-breaking world’s longest hug and the Science of Love (shockingly- it's to do with hormones, not exactly breaking news), now we can tell you all about the world’s smallest ears and the scientist who
discovered them, using only a loudspeaker, a digital camera and some gold.
This
bizarre sounding collection of equipment was an invention borne out of
necessity. When scientists at the Ludwig Maximilian University in Munich could
no longer see what they needed down an optical microscope, they put their
ingenuity to the test and came up with a rather home-made looking contraption.
This experiment means that when they can’t see what they need to down a
microscope, they can hear down it instead.
The
world’s smallest ear is actually the product of long and drawn out research,
led by Jochen Friedmann. Their work, published this month in Physical
Letters,
shows how by trapping gold nanoparticles they can use them as tiny 'ears' to
hear the movement of objects down to cellular level.
The common method of using optical
tweezers -radiation pressure from a laser- to twist and manipulate nano objects
was suggested as a new way of holding the gold nanoparticles in place. The
‘ear’ was only 60 nanometres wide which, to give you an idea, is about the size
of a pea if the pea were the size of the Earth. This static ‘ear’, will only
move if nudged by movement nearby which means it can be used to measure
fluctuations in its environment, fluctuations like an acoustic wave.
Alexander Ohlinger and his
colleagues used a two stage process to develop the ‘ear’. “First, we validated
the basic principle using a relatively strong sound source” group leader Andrey
Lutich explains. “In the second step we were able to detect significantly
weaker acoustic excitations.”
The scientists first glued a tiny
tungsten needle onto a loudspeaker and used this to agitate the gold particles
by sending sound waves towards them. Friedmann could detect the movement of the
particle using a darkfield microscope and an ordinary digital camera to show
the particle moved parallel to the sound waves propagation.
Next, they trapped one gold
nanoparticle in amongst a group of other ‘free’ particles and heated them with
a green laser. It was found that these particles emitted tiny vibrations
towards their static counterpart which could be used to build a 3D image of the
object at nanoscale.
The
unprecendented sensitivity of the world's tiniest ear – it can hear sound a
million times quieter than you or I could- means a whole new swath of
information will be available to us about cells, bacteria and viruses that we
could never have imagined learning just from viewing them down a microscope. In
particular we will be able to ‘see’ into areas where light conditions made the
use of an optical microscope impossible. However, as the experiment stands, it
is only a concept which works in controlled lab environments, and it would need
to be significantly refined in order to be used as a medical tool.