Sunday,
January 18, 2015
EPFL scientists have developed an extremely
sensitive device that can detect life forms by sensing the slightest motion.
The chemistry-free system can be used to rapidly test antibiotics or even to
search for life on other planets.
Looking for
life on other planets is not straightforward. It usually relies on chemical
detection, which might be limited or even completely irrelevant to alien
biology. On the other hand, motion is a trait of all life, and can be used to
identify microorganisms without any need of chemical foreknowledge. EPFL
scientists have now developed an extremely sensitive yet simple motion detector
that can be built easily by adapting already-existent technology. The system
has proven accurate with detecting bacteria, yeast and even cancer cells, and
is considered for the rapid testing of drugs and even the detection of
extraterrestrial life. The work is published in PNAS.
Giovanni
Dietler, Sandor Kasas and Giovanni Longo at EPFL have developed a motion
detector that uses a nano-sized cantilever to detect motion. A cantilever is
essentially a beam that is anchored only at one end, with the other end bearing
a load. The cantilever design is often used with bridges and buildings, but
here it is implemented on the micrometer scale, and about 500 bacteria can be
deposited on it.
The idea
comes from the technology behind an existing microscope, the atomic force
microscope. This powerful microscope uses a cantilever to produce pictures of
the very atoms on a surface. The cantilever scans the surface like the needle
of a record player and its up-and-down movement is read by a laser to produce
an image.
The motion
sensor the Dietler and Kasas developed works the same way, but here the sample
is attached on the cantilever itself. For example, a bacterium attaches to the
cantilever. If the bacterium is alive, it will inevitably move in some way,
e.g. move its flagellum or simply carry out normal biological functions. That
motion also moves the much smaller and sensitive cantilever and it is captured
by the readout laser as series of vibrations. The signal is taken as a
sign of life.
The EPFL
scientists successfully tested their novel system with isolated bacteria,
yeast, mouse and human cells. They even tested soil from the fields around the
EPFL campus and water from the nearby Sorge river. In each case, they were able
to accurately detect and isolate vibration signatures from living cells. When
they used drugs to kill anything alive, the motion signals stopped.
"The
system has the benefit of being completely chemistry-free," says Dietler.
"That means that it can be used anywhere — in drug testing or even in the
search for extraterrestrial life." The scientists envision a large array
of cantilever sensors used in future space exploration probes like the Mars
rover. As it relies on motion rather than chemistry, the cantilever sensor
would be able to detect life forms in mediums that are native to other planets,
such as the methane in the lakes of Titan.
However,
the more immediate applications of the cantilever system are in drug
development. Used in a larger array, the cantilevers could be covered with
bacteria or cancer cells and incubated with various drug compounds. If the
drugs are effective against the attached cells, the motion signals would
decrease or stop altogether as the cells die off. This approach would be
considerably quicker than current high-throughput systems used in by pharmaceutical
companies when looking for candidate antibiotics or anticancer drugs.
"This
is really the next step," says Dietler. "But we're still calling ESA
and NASA to see if they're interested."
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