Bio-based molecules that change colour when they react with ammonia can be used as sensors, reports a Rotterdam-based group in 2023 IEEE Sensors.

Ammonia has applications as a hydrogen carrier, green fuel and reagent. But like many chemicals, you don’t want to inhale it. Especially at concentrations of around 50 ppm, there are health risks that are best avoided, not to mention the potential environmental damage. Jochem Hagenaar, Gennady Oshovsky, Jan Herselman and colleagues at the Rotterdam University of Applied Sciences have therefore developed a colourimetric sensor that can detect the presence of ammonia in the air.

The group produced the sensor in a sustainable way: they made 5-hydroxymethylfurfural from apple waste, which they then converted into two sensor molecules that react with ammonia in the air. They then applied drops with different concentrations of one of the molecules to a strip of filter or printer paper. When the sensors react with ammonia, the colour of the dried spots on the paper changes, which can be seen with the naked eye.

Hagenaar and his colleagues carried out tests in two concentration ranges: from 1 to 50 ppm to simulate the working environment, and above 50 ppm to simulate accidents. At 50 ppm it takes about 10 to 20 minutes before you see a colour change, at 25 ppm it takes 30 minutes and at 1 ppm - the lower limit of the sensor - it takes an hour before you see any colour change. On the other hand, if you go (much) higher than 50 ppm and look at an accident situation, you will have a significant colour signal in five minutes or less.

According to the authors, the applications are numerous. Finding leaks, monitoring ammonia accidents and monitoring ammonia concentrations in agricultural and industrial areas are among the possibilities.

Hagenaar, J.J. et al. (2023) 2023 IEEE Sensors, DOI: 10.1109/SENSORS56945.2023.10324893