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The RADICAL project was recently featured in the HZDR ‘Discovered’ magazine from December 2022, as part of a showcase of innovative research projects focused on improving pollution monitoring and mitigation.

This article includes our English translation of the original German text, by Gabriele Schönherr and all credit for the amazing graphics goes to Ketchum GmbH.

Download: English PDF version of ‘RADICAL: Detecting radicals radically better’

“Radicals affect the chemistry of our atmosphere, our air quality, our environment, our climate and our health.

To what extent, however, is still unknown. This is because these reactive atoms and molecules are very short-lived and their detection is technically very demanding.

In the European RADICAL project, a research team is developing new sensors that could revolutionise previous measurement options. Special nanowire chips are being developed at HZDR for this purpose.”

Credit: HZDR. English translation: RADICAL project

Electronic Nose

How do you catch a radical? What has so far only been possible in a handful of time-consuming measurement campaigns could become commonplace with the help of small electronic sensors. The EU-funded RADICAL project is developing a completely new measurement concept: an “electronic nose” designed to detect free radicals. Specially coated nanowires in the sensor generate electrical signals when they come into contact with the target gases. Readout electronics analyse the signals further – similar to how the human brain processes olfactory stimuli and recognises different smells.

Similar sensors have already demonstrated outstanding sensitivity and selectivity in liquids. In the RADICAL project, researchers are now further developing the technology for gases. And in particular, for gases that are especially difficult to detect: radicals.

Real-time global monitoring

The new electronic sensors are so compact and inexpensive that they will enable comprehensive monitoring: continuously and in real time. If the project is successful, this data will provide direct insights into the complex interaction of radicals in the chemistry of the atmosphere – and thus help to decipher the role of radicals in our air quality, health and environment.

A network of monitoring stations on the ground and in the air already provides a large amount of environmental and weather data on the atmosphere.

The new sensors are designed to be integrated into this network, but they can also work autonomously.

In addition, this electronic nose consumes very little energy and conventional batteries are sufficient for regular data transmission.

“When we install our new sensors at existing monitoring stations, it dramatically improves our capabilities.”

– Yordan Georgiev, HZDR

Nanowire detector

At the heart of the new sensors are tiny chips, just a few square millimetres in size, which are fitted with ultra-thin silicon nanowires and connected to an electrical circuit.

These nanowires serve as a kind of scavenging net for radicals and also transmit electric signals. A special design principle makes them highly sensitive to electrical signals: The wires are known as junctionless nanowire transistors, meaning they do not require the usual semiconductor material structuring, thus reducing signal interference. An additional organic molecule layer applied to the nanowires selectively traps radicals from the ambient air – without reacting with other more common gas molecules. The electrical signal is generated because the trapped radicals are electrically charged and thus change the conductivity of the wire.

Delivering the best

Nanowires are ideally suited as sensitive sensors: the ultrafine wires offer a large detector surface in a very small space. The larger the area, the more likely it is that a radical “goes into the net”, and the lower the gas concentration that can be measured. To develop the sensors, researchers at HZDR are working on wires that are just a few nanometres thin and as smooth as possible. The smallest defect on the surface could scatter or capture charge carriers and falsify the signal. HZDR has one of the few research laboratories in the world that can precisely manufacture such thin wires. With the delivery of the first nanowires, the researchers recently reached an important milestone.

“We were looking for a new challenge for this nanowire technology and we realised: if we want to achieve a significant breakthrough, we must detect radicals.”

– Yordan Georgiev, HZDR

How atmospheric radicals change the air

Air pollution is an increasing problem for our health and the climate. Atmospheric radicals play a key role in the underlying chemical cycles.

Radicals are atoms and molecules that have at least one unpaired electron. They occur naturally in the atmosphere, often fuelled by sunlight. Radicals are very reactive as they search for a new electron. As a result, they contribute to a diverse range of chemical processes.


For example, radicals help the atmosphere cleanse itself of pollutants. The hydroxyl radical (OH) acts as an antagonist to the greenhouse gas methane – which is why it is sometimes referred to as the “atmosphere’s detergent”.


However, the breakdown of trace gases by radicals produces pollutants such as ozone, hydroperoxides, acids and particulate matter. For example, hydroxyl radicals convert nitrogen and sulphur dioxide into acid, which can dissolve in cloud water droplets and fall as acid rain.

Read more: “How atmospheric radicals transform the air” by John Wenger, RADICAL researcher and UCC atmospheric chemist



Tailor-made nanowires and sensor chips are created at HZDR. Models from the Bulgarian company Smartcom help with the design for manufacture.


Experts from the University of York in the UK and the National Technical University of Athens in Greece apply a layer of organic molecules to the nanowires. The molecules are designed to capture radicals with pinpoint accuracy.


Experimental tests at University College Cork in Ireland improve the measurement quality of the sensors.


The finished sensors are tested in special atmosphere simulation chambers at University College Cork as well as in ambient air.


Through publications, networking and industry collaborations, the project is designed to quickly bring the sensor technology into broad application.

Download: English PDF version of ‘RADICAL: Detecting radicals radically better’

Follow our progress with RADICAL