A small sensor that detects toxic gases shows promising results in the lab

A team of scientists at UNSW Sydney has developed a small, highly sensitive sensor that can detect low concentrations of the toxic gas nitrogen dioxide (NO2). The small, flexible sensor can detect harmful gases in real time without the need for an external energy source.

Gas sensors are used in a wide range of applications, especially in health and safety regulations, including monitoring the presence of flammable, combustible, and toxic gases.

The sensor is approximately 2cm x 2cm and only 0.4mm thick and has the potential to overcome some of the existing limitations of gas sensors, such as size limitations, high cost, and energy consumption.

The new prototype, developed by Jiyun Kim, Dr Tao Wan, Dr Long Hu, Professor Dewei Chu and a team from UNSW’s School of Materials Science and Engineering, is highly sensitive to NO2 and can operate at room temperature.

The latest research, published in the journal Advanced Science, also outlines how the sensor’s key components were sustainably produced using advanced printing techniques.

“This is very interesting because it’s not science for science’s sake, but has great potential for practical applications,” says Professor Chu.

“The fact that it is sustainable and shows good performance makes us feel like we are contributing to a revolution in gas sensors that can be implemented in wearable sensing applications and large-scale production.”

What is a gas sensor used for?

Gas sensors are widely used for various purposes. It is most commonly used for health and safety purposes, such as detecting dangerous levels of toxic gases such as carbon monoxide (CO) and NO2. NO2 levels can be particularly high in areas with many sources of emissions, such as busy roads, factories, and power plants.

“Other gas sensors include gas sensors in car engines that detect oxygen levels,” Professor Chu says. “This is because the fuel-to-oxygen ratio needs to be adjusted to get good efficiency.

“They are also used in medical settings, such as identifying the components of people’s breath.”

However, these existing sensors have several limitations, such as their size and high energy consumption required for operation, limited sensitivity and sensor degradation over time.

“Current gas sensors can be complex, which also means they can be very expensive,” Professor Chu says. “For example, oxygen sensors in glove boxes cost $5,000 each.”

Addressing these challenges requires continued research and development to improve accuracy, reliability, and versatility. So Professor Chu and his team set out to create a lightweight and affordable sensor to detect NO2.

2D printing as a sustainable production technology

The research team began their work with molybdenum disulfide (MoS2), a well-known and promising compound that has been previously used for sensing applications due to its sustainability and biocompatibility.

“My research group has been studying the potential of MoS2 as a sensing device for more than eight years,” says Professor Chu.

“There are two different subgroups of MoS2, one that is more conductive and one that is less conductive.

“We found that the combination of the two subgroups provides an optimal gas sensor compound that is sensitive to external gas composition and can maintain electrical conductivity, which is essential for these sensors.”

After combining the two subtypes of MoS2, the team made several additional changes to the soluble compound. “For example, we added nitrogen to the soluble mixture to increase sensitivity,” says Professor Chu.

When NO2 molecules damage a surface, MoS2 compounds have the ability to absorb them. “Trapping NO2 molecules changes the electrical resistance of the surface, allowing us to record changes in conductivity at room temperature.”

What’s even more unique about this mini-sensor is that it’s built using 2D printing technology.

“2D printing technology is similar to 3D printing, except that it is done on very fine surfaces to minimize the manufacturing cost of the sensor,” says Professor Chu. “The process involves small nodules that inject soluble substances into a flat surface.”

The team used this 2D printing to build two components of the sensor. “We actually use 2D printing to print conductive nanomaterials that act as sensor electrodes,” Professor Chu says. “Next, we print the sensor material itself, which is MoS2, which we developed in our lab.”

Promising initial results

Existing commercial gas sensors face significant problems due to high energy consumption, low accuracy, slow real-time monitoring, and lack of ability to detect trace concentrations, which limit their development and various applications. Masu.

“The principle of gas sensors currently on the market is that they need to be heated, sometimes up to 300 degrees Celsius, otherwise they cannot be detected,” says Professor Chu. “Our device can operate at room temperature, so it requires much less energy.”

Lab tests showed that the company’s MoS2-based sensor has a sensitivity as high as 10ppm NO2. This means that the sensor can successfully detect 10 NO2 particles out of 1 million gas particles.

NO2 naturally exists in the air in trace amounts, but the main source is human activities such as coal burning, and high concentrations of the gas pose a danger to human life. NO2 concentrations between 50 and 100 ppm can cause delayed lung damage, and above 200 ppm are considered an immediate danger to life.

Next generation gas sensing technology

Thanks to its small size and low energy consumption, this wearable device can be used in a wide range of applications, especially when it comes to safely measuring gas concentrations in different working environments.

“We want to work on designing wearable sensing devices to monitor air quality, such as in industrial safety systems at mining sites and warehouses, where NO2 concentrations can be particularly high,” Professor Chu said. I say.

Professor Chu explains that although this development is a major step in next-generation gas sensor technology, there is still room for improvement, including testing sensitivity to other gases, which would widen the range of potential applications.

“Safety issues limit access to a wide range of gases, including volatile organic compounds and other toxic gases such as ozone-3 and carbon dioxide,” he says. “It would be great to be able to test a wider range of gases to evaluate how our sensor performs on other target gases.”