Vietnamese doctor makes a sensor to detect ammonia gas

Dr. Nguyen Chung and his colleagues in Australia are researching the development of a microscopic sensor capable of detecting ammonia gas in breath, warning of health problems.

Dr. Nguyen Chung , 35 years old, researcher of Vietnamese origin at RMIT (Australia), main author, is the only Vietnamese member along with scientists from RMIT University (Australia), University of Melbourne and Export Center The Australian Research Council (ARC) Institute of Photonic Nanosystems (TMOS) conducted the research.

The sensor consists of a transparent and ultra-thin tin oxide film, which can easily detect ammonia at much smaller levels than similar technologies. The device works like an electronic "nose" capable of detecting even the smallest amount of ammonia. The sensor can also differentiate between ammonia and other gases with greater accuracy than other technologies.

Speaking to PV , Dr. Nguyen Chung said the research idea was born in early 2022. The project took nearly a year to complete most measurements in May 2023. The research was published in the leading materials science journal Advanced Functional Materials in November 2023.

The research team attached ultra-thin tin oxide to the substrate material. (Photo: Seamus Daniel/RMIT).

Dr. Nitu Syed, head of the research team, said that the presence of ammonia in the air changes the resistance of the tin oxide film in the sensor, meaning that the higher the ammonia concentration, the greater the change in resistance of the device. . The team conducted experiments with the sensor in a specially designed device to test its ability to detect ammonia gas at different concentrations (5 - 500 ppm) and conditions, including temperature. . They also tested the device's accuracy in distinguishing ammonia from other gases, including CO ₂ and methane. The results demonstrate that this sensor can detect ammonia in very small concentrations, so it can be designed to detect ammonia in breath to warn about potential health disorders.

To make the sensor, the team used a low-cost and easily replicable technique of attaching ultrathin tin oxide to a substrate material . This technique is feasible even on flexible materials - which often make other fabrication methods difficult. The team obtained a tin oxide film from a molten tin surface at a temperature of 280 degrees Celsius. This film is 50,000 times thinner than paper . "Our method requires only a single synthesis step without any toxic solvents, vacuum environments or bulky and expensive instruments ," said Dr. Ylias Sabri, University Faculty of Engineering RMIT (Australia), description.

Principal researchers include Dr Nitu Syed, Dr Ylias Sabri and Dr Nguyen Chung (from left) in the laboratory at RMIT University. (Photo: Seamus Daniel/RMIT)

Dr. Nguyen Chung said, this miniature sensor provides a safer and more compact solution for detecting toxic gases compared to existing techniques. Current ammonia detection methods provide accurate measurements but require expensive laboratory equipment and qualified technicians, and require many samples and elaborate preparation. This process is often time-consuming and immobile due to the bulky size of the equipment. In addition, to produce ammonia detection sensors, expensive and complex processes are needed to prepare sensitive material layers for sensor manufacturing.

The team's new sensor can instantly distinguish safe or dangerous levels of ammonia in the environment. "This tin oxide mounting technique can be scaled up, thus providing the opportunity for mass production at a more reasonable cost ," he said.

He said the team had difficulty characterizing the material because of the material's ultra-thin nature (the team's tin oxide is only 2 nanometers thick). Setting up a reliable gas measurement system is also a challenge. However, the cooperation of many researchers and experts from RMIT University and the University of Melbourne helped the team overcome the challenge.

The team hopes to cooperate with industry partners to continue developing and manufacturing the next version of the sensor to optimize the performance of this type of sensor. The team's method is compatible with existing manufacturing processes in the silicon industry, and is therefore suitable for mass production.

An estimated 235 million tons of ammonia are produced globally each year to meet the needs of many industries. Ammonia is promoted as one of the effective methods for storing hydrogen in green fuel production, and ammonia production is expected to increase over the next few years.

However, exposure to excessively high concentrations of ammonia can lead to chronic lung disease and irreversible organ damage. Ammonia gas leaks during transportation and plant operation pose many risks and can be deadly. Therefore, the ability to detect ammonia effectively and reliably is essential to ensure safety. This gas is also found in human breath and can be used as an important "biomarker" for diagnosing many diseases such as kidney and liver related disorders.

Dr. Nguyen Chung received a Master's degree in Chemical Engineering from Ho Chi Minh City University of Technology in 2014. He is currently a researcher at the Faculty of Engineering, RMIT University, his research field mainly focuses on liquid metal chemistry. and synthesizing 2D materials for use in electronics and sensing applications.