Nanotechnology 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 devices.
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 networks of air quality monitoring stations to improve the tracking of air pollution sources.
Researchers at MIT have demonstrated a sensor using carbon nanotubes that are coated with a polymer. The molecule that each sensor is sensitive to depends upon the spacing of polymer loops around the nanotube. The researchers believe that this method will allow the production of sensors to detect molecules that cannot be detected with sensors that use anitbodies to detect molecules.
Researchers at Lawrence Livermore Labs have developed a sensor using carbon nanotubes coated layers of hafinium and gold. They believe that these sensors can detect extremely low concentrations of molecules indicating biological threats or explosives.
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 windshield. When hydrogen is absorbed the palladium nanoparticles swell, causing shorts between nanoparticles which lowers the resistance of the palladium layer.
Sensor containing a monolayer of molybdenum disulfide which changes resistance when exposed to a chemical present in nerve gas.
Sensors containing 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 vapors.
Sensors using carbon nanotube detection elements capable of detecting a range of chemical vapors.
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 layer.
Chemical sensor using nanocantilevers that are oscillating at their resonance frequency. When the chemical 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 cantilever changes.
Sensors using 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.
Compiled by Earl Boysen of Hawk's Perch Technical Writing, LLC and UnderstandingNano.com. You can find him on Google+.