Beyond the sensitivity of most indoor air quality sensors, researchers have created a sensor made of “frozen smoke” that uses artificial intelligence techniques to detect formaldehyde in real-time at concentrations as low as eight parts per billion.
Sensor Technology Offers Real-Time Detection of Hazardous Gases" />
Silica aerogel. Image Credit: NASA/JPL-Caltech
University of Cambridge researchers created sensors using aerogels, which are extremely porous materials. The sensors were able to identify formaldehyde, a common indoor air pollutant, at room temperature by carefully designing the holes in the aerogels.
The low-power proof-of-concept sensors could be reduced in size for wearable and medical applications, and they could be modified to identify a variety of dangerous gases. The researchers published their work in the journal Science Advances.
One of the main causes of indoor air pollution is volatile organic compounds (VOCs), which can lead to elevated levels of breathing difficulties, burning in the eyes and throat, and watery eyes. Asthma sufferers may experience attacks at high concentrations, and prolonged exposure may result in some cancers.
Common household products that release formaldehyde include paints and wallpaper, pressed wood products (like MDF), and certain synthetic textiles. Although these products do not release a lot of formaldehyde, over time, they may, particularly in garages where paints and other products that release formaldehyde are more likely to be kept.
A 2019 study by the advocacy organization Clean Air Day revealed that formaldehyde concentrations were noticeable in one-fifth of UK households, with 13% of homes having formaldehyde concentrations above the WHO’s recommended limit.
VOCs such as formaldehyde can lead to serious health problems with prolonged exposure even at low concentrations, but current sensors don’t have the sensitivity or selectivity to distinguish between VOCs that have different impacts on health.
Tawfique Hasan, Professor and Lead Researcher, Cambridge Graphene Center, University of Cambridge
Zhuo Chen, the study’s first author, says, “We wanted to develop a sensor that is small and doesn’t use much power, but can selectively detect formaldehyde at low concentrations.”
Aerogels are incredibly light materials that are often referred to as “liquid smoke” because they contain more than 99% air by volume. This is how the researchers built their sensors. Gases can enter and exit aerogels with ease due to their open structure. The morphology, or precise engineering, of the holes allows the aerogels to function as extremely sensitive sensors.
The Cambridge researchers, in collaboration with their Warwick University counterparts, refined the aerogels’ composition and structure to enhance their sensitivity to formaldehyde, transforming them into filaments roughly three times as wide as a human hair.
To create the holes in the final aerogel structure, the researchers first 3D printed lines of a paste made of graphene, a two-dimensional form of carbon. The graphene paste was then freeze-dried. Additionally, the aerogels contain quantum dots, which are minuscule semiconductors.
They created sensors that could identify formaldehyde at as low as eight parts per billion, or 0.4 percent of what is considered safe in UK workplaces. The sensors require very little power and function at room temperature as well.
Traditional gas sensors need to be heated up, but because of the way we’ve engineered the materials, our sensors work incredibly well at room temperature, so they use between 10 and 100 times less power than other sensors.
Zhuo Chen, Study First Author, Cambridge Graphene Center, University of Cambridge
The researchers then added machine learning algorithms to the sensors to increase selectivity. The formaldehyde fingerprint was distinguished from other volatile organic compounds (VOCs) by the sensor thanks to algorithms trained to identify the “fingerprint” of various gases.
Hasan says, “Existing VOC detectors are blunt instruments – you only get one number for the overall concentration in the air. By building a sensor that can detect specific VOCs at very low concentrations in real time, it can give home and business owners a more accurate picture of air quality and any potential health risks.”
According to the researchers, other VOCs could be detected by sensors using the same methodology. Theoretically, a device the size of a typical home carbon monoxide detector could contain several different sensors, giving it the ability to monitor a variety of dangerous gases in real-time.
At Warwick, we’re developing a low-cost multi-sensor platform that will incorporate these new aerogel materials and, coupled with AI algorithms, detect different VOCs.
Julian Gardner, Co-Author and Professor, Warwick University
Chen concludes, “By using highly porous materials as the sensing element, we’re opening up whole new ways of detecting hazardous materials in our environment.”
The research was supported in part by the Henry Royce Institute and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI). Tawfique Hasan is a Fellow of Churchill College, Cambridge.
Journal Reference
Chen, Z., et.al (2024) Real-time, noise and drift resilient formaldehyde sensing at room temperature with aerogel filaments. Science Advances. doi.org/10.1126/sciadv.adk6856