Solid-state ammonia sensor based on Berthelot’s reaction

A non-reversible solid-state ammonia sensor based on formation of indophenol blue has been developed. A new optimised reaction conditions found for Berthelot’s reaction allow the sensor to respond to dissolved ammonia in ambient conditions at a much faster reaction rate than previously known. This solid-state colorimetric sensor reaches maximum colour intensity in ∼3 min at room temperature (∼20 °C) and responds linearly to ammonia between 1 and 10 ppm. A semi-automatic imaging system that consists of a black and white digital camera illuminated by red, green and blue LEDs was developed to measure the sensor responses.