and Biological Sensors using Nanotechnology
How can nanotechnology improve
chemical and biological sensors?
can enable sensors to detect very small amounts of chemical vapors.
Various types of detecting elements, such as carbon nanotubes, zinc oxide nanowires or
palladium nanoparticles can be used in nanotechnology-based sensors.
These detecting elements change
their electrical characteristics, such as resistance or capacitance, when
they absorb a gas molecule (for technical details see this article).
Because of the
small size of nanotubes, nanowires, or nanoparticles, a few gas
molecules are sufficient to change the electrical properties of the
sensing elements. This allows the detection of a very low concentration of chemical vapors. The
goal is to have small,
inexpensive sensors that can sniff out chemicals just as dogs are used
in airports to smell the vapors given off
by explosives or drugs.
The capability of
producing small, inexpensive sensors that can quickly identify a chemical vapor
provides a kind of nano-bloodhound that
doesn't need sleep or exercise which can be useful in a number of ways. An
obvious application is to mount these sensors throughout an airport, or
any facility with security concerns, to check for vapors given off by explosive
These sensors can also be useful in industrial plants that use chemicals
in manufacturing to detect the release of chemical vapors. When
hydrogen fuel cells come into use, in cars or other applications, a
sensor that detects escaped hydrogen could be very useful in warning of
a leak. This technology should also make possible inexpensive
of air quality monitoring stations to improve the tracking of
air pollution sources.
Applications under Development
Researchers at the University of Utah are developing
explosive sensors using
carbon nanotubes. They bond polymers to the carbon nanotubes to tune
the nanotubes to different explosives or chemical vapors.
Reseachers at MIT have developed a sensor using carbon nanotubes
embedded in a gel; that can be injected under the skin to
monitor the level of
nitric oxide in the bloodstream. The level of nitric oxide is
important because it indicates inflamation, allowing easy monitoring of
imflammatory diseases. In tests with laboratory mice the sensor remained
functional for over a year.
Researchers at the Technische Universität München have demonstrated a
method of spraying carbon
nanotubes onto flexible plastic surfaces to produce sensors. The
researchers believe that this method could produce low cost sensors on
surfaces such as the plastic film wrapping food, so that the sensor
could detect spoiled food.
Hydrogen sensor using a layer of closely spaced palladium
nanoparticles that are formed by a beading action like water on a
hydrogen is absorbed the palladium nanoparticles swell, causing
shorts between nanoparticles which lowers the resistance of the
Sensor containing a
monolayer of molybdenum disulfide which changes resistance when
exposed to a chemical present in nerve gas.
sheets of graphene in the form of a foam which changes resistance
when low levels of vapors from chemicals, such as ammonia, is present.
Sensors using zinc oxide nano-wire
detection elements capable of detecting a range of chemical
carbon nanotube detection elements capable of detecting a range of
Sensors using a layer of
gold nanoparticles on a polymer film for detecting volatile organic
compounds (VOCs). The polymer swells in presence of VOCs, changing the
spacing between the gold nanoparticles and the resistance of the gold
Chemical sensor using nanocantilevers that are oscillating
at their resonance frequency. When the
attaches to the cantilever it stops the oscillation, which triggers
a detection signal. Nanocantilevers can also be used to
detect biological molecules, such as viruses. The cantilever is
coated with antibodies that capture the particular virus, when a virus
particle attaches to the an antibody the resonance frequency of the
nanoporous silicon detection
elements that could be incorporated into cell phones. This might
allow a very widespread network of sensors to detect chemical gas leaks
or release of a toxin.
Sensors powered by electricity generated by
piezoelectric zinc oxide nanowires. This could allow
small, self contained, sensors
powered by mechanical energy such as tides or wind.