Advanced detectors based on carbon nanotubes are expected to improve our ability to know when the food packaging is not valid or when the air in the room is dangerous to breathe. Just don't accidentally swallow them.
Researchers at the Technical University of Munich (TUM) are moving towards cheap, industrial production of a new family of electronic devices. One of the leading examples in this family is a gas detector that can be embedded inside food packages in order to measure the freshness of the product, or inside wireless monitoring devices to check air quality. In addition, the technology could lead to the development of new types of solar cells and flexible transistors as well as the development of pressure and temperature sensors that could be installed inside electronic skin in robotic or bionic applications. The key to these developments is carbon nanotubes that can be sprayed onto flexible plastic sheets or other types of substrates.
These gas detectors provide a unique combination of features that could not be achieved until now with any other alternative technology. These detectors are able to quickly detect and continuously respond to small changes in the concentrations of various gases, including ammonia, carbon dioxide and nitrous oxide. They are the ones that operate at room temperature and consume only little energy.
In addition, the researchers claim that such devices could be anchored on flexible surfaces using cheap and industrial processes. Thus, it is possible to imagine plastic covers for food in which there are flexible and disposable gas sensors that will be used as a kind of "smart packaging" that will be able to provide an effective indication of the freshness of the food, instead of the expiration dates that are in use today. Measuring carbon dioxide gas concentrations, for example, could help predict more accurately the shelf life of meat products.
Such smart packaging has many advantages: it can increase food safety and possibly even reduce the amount of food thrown into the waste. Additional use of these gas detectors could reduce the costs of monitoring equipment to check air quality in real time inside buildings. At the same time, it will be a long time before the cottage in the refrigerator will inform us when it is broken: first, consumers will have to get used to them and trust the measured information, and proof will be required that the devices themselves are not toxic to the environment.
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spray black ink
The researchers showed that it is indeed possible to spray high-performance gas detectors on flexible plastic substrates. This method paves the way for the commercial application of detectors based on carbon nanotubes. "It's really simple – of course, once you know how to do it," says Professor Paolo Lugli, director of the German Research Institute.
The most basic building block of this technology is a single cylindrical molecule - a rolled sheet of carbon atoms connected together in a honeycomb pattern (hexagons). Such a carbon nanotube can be connected to obtain an extremely long tube - a hollow tube with a diameter of single nanometers and a length that is millions of times greater than this value. Individual carbon nanotubes have wonderful and valuable properties, especially electronic properties, but the researchers are focusing in this case on the application of a large amount of them.
Carbon nanotubes placed in the form of thin layers and randomly form electrically conductive networks that can be used as electrodes; Layered and patterned layers can function as sensors or transistors. "Actually," explains the researcher, "the electrical resistance of such layers can be changed in two ways: by changing the electrical voltage that flows through them (to obtain the activity of a transistor) or by the adsorption of gas molecules, which in turn constitute a distinct sign and a type of signature as to the concentration of the gas, while receiving gas detector activity."
, as a basis for a gas detector, carbon nanotubes uniquely incorporate many advantages compared to more common devices in this field, such as organic electronic components based on polymers and solid-state semiconductors.
The link that was missing until now was a reliable, flat and cheap production method of such carbon nanotubes. The method of 'Spray deposition' can be the solution. An aqueous solution of carbon nanotubes looks like liquid black ink and can be used in similar ways: these devices—from computer-controlled robotic mouthpieces to larger elements—can be sprayed onto any type of substrate, including vast sheets of flexible plastic. Therefore, there is no need for expensive facilities that include clean rooms (similar to the chip manufacturing industry). "It was important for us to develop a technological method that can be easily transferred to an industrial scale for the production of large, printed and flexible electronic components, based on organic semiconductors and nanomaterials," explains one of the researchers. "So the spray layering method forms the core of our technological process." Now the researchers will have to deal with additional technological challenges arising mainly from requirements for specific applications of the development, such as the need for the gas detectors to be as selective as possible, and also particularly sensitive.
For information on the university website
