New nose-shaped sensor detects toxic ammonia gas

Australian engineers have developed a small ammonia gas sensor that could enable safer hydrogen storage and specialist medical diagnostic devices.

The simple but effective proof-of-concept sensor described in Advanced functional materials is the result of the collaboration of researchers from RMIT University, the University of Melbourne and the ARC Center of Excellence for Transformative Meta-Optical Systems (TMOS).

Exposure to high levels of ammonia can lead to chronic lung disease and irreversible organ damage.

An estimated 235 million tonnes of ammonia are produced worldwide, but with ammonia being touted as one of the best ways to store hydrogen to produce a clean fuel, we could see a lot more. Reliable and sensitive ammonia detection will be essential to quickly detect potentially dangerous leaks of gaseous ammonia during hydrogen transport to ensure safe operation.

But while human exposure to ammonia can be harmful, this gas is also present in human breath and can serve as a vital biomarker for the diagnosis of many diseases such as kidney and liver-related disorders. Since the team’s sensor can measure tiny amounts of ammonia, it could be designed to detect the gas in people’s breath to alert doctors of health problems.

How the sensor works

Lead principal investigator Dr Nitu Syed said the sensor contained atomically thin transparent tin dioxide that can easily track ammonia at much lower levels than similar technologies.

“Our device acts like an electrical ‘nose’ by effectively detecting even the smallest amount of ammonia,” said Syed, a McKenzie researcher from the University of Melbourne, RMIT and TMOS. “The sensor is also able to distinguish ammonia from other gases with more selectivity than other technologies.”

The presence of ammonia in the air modifies the electrical resistance of the tin oxide film in the sensor: the higher the ammonia level, the greater the change in the resistance of the device.

The team conducted experiments with their sensor in a specially designed chamber to test its ability to detect ammonia at various concentrations (5 to 500 parts per million) under different conditions, including temperature. They also tested the device’s ammonia selectivity over other gases, including carbon dioxide and methane.

First author Dr Chung K. Nguyen from RMIT said their miniaturized sensor offered a safer and less bulky way to detect the toxic gas, compared to existing techniques.

“Current ammonia detection approaches produce accurate measurements but require expensive laboratory equipment with trained technicians, extensive sampling and preparation,” Nguyen said. “This process is often time-consuming and not portable, due to the size of the equipment needed. Additionally, manufacturing current ammonia detectors involves expensive and complicated processes to prepare the sensitive layers for manufacturing sensors.”

The team’s new sensor can instantly differentiate between safe and unsafe levels of ammonia in the environment, Nguyen said.

“Reproducible tin oxide deposition also offers the opportunity for cost-effective mass production of sensing devices,” he noted.

How is the sensor made?

Dr Ylias Sabri, co-principal investigator from RMIT’s School of Engineering, said the team used a low-cost and scalable technique to deposit very fine tin dioxide onto a base material, even on a flexible material, a result that other approaches have encountered. challenges to overcome to achieve this.

“We directly harvest a tin oxide film from the surface of molten tin at 280 degrees Celsius. The film is 50,000 times thinner than paper,” Sabri said. “Our approach requires only a single synthesis step, without the use of toxic solvents, vacuum, or bulky and expensive instrumentation.”

The team aims to collaborate with industry partners to further develop and prototype the sensor to demonstrate its high-performance sensing capabilities, saying: “The manufacturing method aligns well with existing manufacturing processes in the silicon industry , making it suitable for mass production. »