University of Cambridge sensor detects formaldehyde concentrations as low as eight parts per billion (University of Cambridge).
Researchers from the British University of Cambridge have developed a sensor made of airgel, or what is known as “airgel” (a solid material consisting of a gelatinous substance in which the liquid component has been replaced with a gas), to detect concentrations as low as eight parts per billion of a volatile organic compound known as Known as “formaldehyde,” it far exceeds the sensitivity of most indoor air quality sensors.
Volatile organic compounds are a major source of indoor air pollution, causing watery eyes, burning in the eyes and throat, and difficulty breathing at high levels. High concentrations can lead to attacks in people with asthma, and prolonged exposure may cause some types of cancer.
The World Health Organization recommends that the level of formaldehyde in the air of offices and homes not exceed 0.1 parts per million (artificial intelligence image)
Why focus on formaldehyde?
Formaldehyde is one of these volatile organic compounds, and is emitted by household items including particle board products, wallpaper, paints, and some synthetic fabrics.
For the most part, levels emitted by these tools are low, but can accumulate over time, especially in “warehouses,” where paints and other products emitting this compound are likely to be stored.
It can also lead to serious health problems even at low concentrations, and the risks increase with high levels, which a report issued by the Clean Air Day Campaign group in Britain in 2019 warned of.
According to this report, formaldehyde exceeded the limit permitted by the World Health Organization in 13% of homes in the United Kingdom, but blood analysis of the families living in these homes showed the presence of the compound in the blood of a fifth of these families.
The organization recommends an average concentration in indoor air of no more than 0.1 parts per million, or 100 micrograms per cubic meter over 30 minutes.
Because of the danger posed by this compound even at low levels, there was a need to create a sensor to monitor air quality, with a focus on detecting it even at very low levels, which the researchers succeeded in doing and which was announced in the study published in the journal Science Advances.
How do current sensors work?
Currently available indoor air quality sensors do not achieve high selectivity at low levels of formaldehyde, and operate according to a set of different detection principles such as:
Electrical resistance:
Sensors based on this method rely on changing their electrical resistance when exposed to certain gases, and then the change in resistance is linked to the concentration of the target gas.
Photoionization:
Sensors based on this method use ultraviolet light to ionize gas molecules, resulting in the formation of positively charged ions. The ions are then detected and their concentration measured.
Optical sensors:
Optical sensors measure the absorption or scattering of light by gases in the air, and can detect gases such as carbon dioxide and particulate matter by analyzing changes in light intensity.
Electrochemical sensors:
These sensors rely on chemical reactions at the electrodes to produce an electrical signal proportional to the concentration of the target gas, and they are usually used to detect gases such as carbon monoxide and nitrogen dioxide.
Solid State Sensors:
Solid state sensors use semiconducting materials to detect gases, and changes in electrical conductivity due to absorption of the gas are measured to determine the gas concentration.
“Airgel, which is the basic material in the sensor, is characterized by surface porosity that allows gases to move in and out easily (Science Advances)
3 advantages of the new sensor
The mechanism of action of these available sensors requires high energy, is not sensitive to very low levels of compounds, and does not achieve high selectivity for a particular compound.
The new sensor overcomes these three negatives and turns into three advantages that give it an advantage, as the new study revealed.
According to the press release issued by the University of Cambridge, these advantages were achieved as follows:
Sensitivity:
The “airgel”-based sensor developed by the researchers shows much higher sensitivity compared to conventional sensors, as it can detect formaldehyde at concentrations as low as eight parts per billion, far exceeding the sensitivity of most existing sensors.
Selectivity:
The sensor is designed to be highly selective for formaldehyde, and this allows it to distinguish this compound from other VOCs more accurately, providing a more accurate assessment of indoor air quality.
Energy Efficiency:
Unlike traditional sensors that often require heating elements or consume significant power, an “airgel” based sensor operates effectively at room temperature and consumes minimal energy, making it more energy efficient and suitable for applications where Where power consumption is a concern, such as wearable devices or continuous monitoring systems.
AI-powered design
The researchers succeeded in achieving these three advantages through an innovative design of the new sensor and its support with artificial intelligence, and relied on seven steps detailed by the professor at the Cambridge Graphene Center and the main researcher of the study, Tawfiq Hassan, in the press release issued by the university, which are:
1- Material selection:
The researchers chose “airgel” as a basic material for their sensor, because it is a very porous material with an open structure that allows gases to move in and out easily.
2- Geometric design of the airgel structure:
The shape of the holes in the airgel is precisely designed, and this geometry is crucial because it determines its ability to capture certain molecules.
3- Merging graphene and quantum dots:
The researchers used graphene (a two-dimensional form of carbon) to create a paste. They printed three-dimensional lines of this graphene and pasted them on the “air gel” structure. Then they freeze-dried the graphene paste to form holes in it. They also incorporated small semiconductors. Called “quantum dots” in its structure, this step enhances the sensitivity of the sensor.
4- Testing and optimization:
The team tested different compositions and structures of the “airgel” to improve sensitivity to formaldehyde, and they modified factors such as the size and distribution of pores in the airgel to maximize the sensor’s ability to detect compound molecules.
5- Calibrating the sensor:
Once the “airgel” structure was optimized, the researchers calibrated the sensor to specifically detect formaldehyde, and used artificial intelligence algorithms to train the sensor to recognize the unique “fingerprint” of the compound’s molecules among other VOCs.
6- Evaluation of the sensor’s performance:
The researchers evaluated the sensor’s performance and tested its ability to detect the desired compound at different concentrations. They found that it could detect it at concentrations as low as eight parts per billion, which indicates its high sensitivity.
7- Application Development:
The researchers then explored potential applications for their sensor technology, envisioning miniature sensors that could be integrated into wearable devices or healthcare systems to monitor indoor air quality in real time.
Sensitivity, selectivity and energy efficiency are three advantages of the new sensor over currently available alternatives (Shutterstock)
4 conditions for practical application
The preliminary results reached by the researchers in their experiments on the new sensor appear to be very good, but they are not enough to grant it a pass for practical application, says Mustafa Abdel Qader, professor of chemical engineering at the Egyptian University of Beni Suef.
In a telephone interview with Al Jazeera Net, Abdul Qader believes that there are four main conditions that must be met in order to be certain of the suitability of the sensor for practical application, which are:
Consistent performance across different environmental conditions, this requires further validation and testing to ensure the sensor's reliability and high sensitivity in different real-world scenarios.
Ensuring the stability of its performance in the long term, and this requires subsequent studies to ensure its reliability over time.
Studying scalability, researchers may need cost and manufacturability studies to facilitate widespread adoption of sensor technology in real-world environments.
Ensuring that sensor data is presented to end users in an easy and efficient manner, this may require subsequent studies to develop user-friendly algorithms for analyzing sensor data.
Source: Al Jazeera + websites