Ammonia (NH3) acts as a precursor for nucleotide and amino acid synthesis and is crucial for plant growth by providing nitrogen. The biogeochemical nitrogen cycle is a bacterial action that creates ammonia in the natural world. Ruminant digestion is one of the primary mechanisms for ammonia formation in natural settings.
How Ammonia is Produced in Nature and Industries
According to industry estimates, 235 million metric tons of ammonia were produced globally in 2019, and that number is projected to rise to approximately 290 million metric tons by 2030.
In agriculture, about 80% of ammonia is utilized to create fertilizer, responsible for 50% of world food production. Ammonia is a recognized sustainable and renewable energy source that may be found in refrigerant gas, polymers, fabrics, cleaning products, and explosives.
Most ammonia emissions come from regions with intensive agricultural, industrial and household activities. These emissions predominate over natural sources. The extensive usage of ammonia impacts human health and life expectancy because it exposes humans to ammonia via inhalation of toxic gas or vapors.
Hazardous Properties of Ammonia
Ammonia is an explosive, poisonous, colorless substance with an unpleasant odor. Inhaling a high dose of ammonia may result in lung conditions and irreversible blindness. Ammonia may be detected in the air in quantities as low as 5 ppm because of its strong odor.
Continuous exposure to gaseous ammonia—even at low concentrations—causes olfactory fatigue or adaptation. Since odor sensitivity varies widely across individuals, people exposed to ammonia for an extended period, including those who work in industrial environments, lose awareness of the offensive smell. Therefore, industrial facilities with on-site personnel need warning and alarm systems for gaseous ammonia.
Techniques Used for Ammonia Detection
Researchers have developed a variety of detection techniques for ammonia gas. In many industries, photoacoustic spectroscopy and laser‐coupled spectroscopy-based gas sensors are applied for ammonia detection, particularly in plants for ammonia production.
The metal-oxide gas sensors' good process compatibility and simplicity have been widely used in ammonia detection, particularly MoO3, TiO2, WOW3, ZnO, and SnO2. Similarly, chemiresistors provide a quick response time with a low detection limit by using conductive polymer.
Despite advantages such as continuous monitoring capabilities and high sensitivity, these techniques have disadvantages, including high costs and requiring complicated equipment to be operated by a skilled person; hence, these techniques are not suitable for small ammonia production facilities.
The researchers of this study considered it imperative to build and implement a simple, disposable, and cost-effective sensor.
Low Cost, Flexible and Attachable Colorimetric Ammonia Detecting Sensor Developed
The researchers used a Bromocresol green (BCG) indicator embedded in thin polydimethylsiloxane (PDMS) films to create a colorimetric film sensor to detect gaseous ammonia.
BCG is a well-known pH indicator that shows a noticeable color shift from yellow to blue when the pH rises from 3 to 6.
A prominent absorption band was only seen at 400–500 nm at low pH levels of 3–4, but pH values greater than 5 revealed an absorption band at 600–700 nm. It was anticipated that BCG's low pKa value would cause it to react quickly with amine-based compounds such as trimethylamine, dimethyl amine, and ammonia.
Fabrication of the Colorimetric Ammonia Gas Sensor
A spin-casting process helped create the colorimetric ammonia gas sensor using bare PDMS and a BCG/PDMS combination.
The bottom PDMS layer was put on a Petri plate. The middle PDMS layer was added over the bottom PDMS layer, and finally, a top PDMS layer was added onto the BCG-incorporated PDMS sensing layer.
PDMS's transparency makes it suitable for optical detection. A thin and flexible colorimetric sensor was mass-produced using this straightforward manufacturing technique.
Upon experimentation using sensors with different BCG concentrations, the researchers noticed that the time required by the sensor to acquire the desired saturation is increased with an increase in BCG concentration.
Significant Findings of the Study and Future Outlooks
The researchers successfully developed a colorimetric sensor based on PDMS film that can detect ammonia gas in the air.
The film sensor was shown to have the benefits of scalability, repeatability, stretchability, and nonleachability when three layers were combined. Since ammonia leakage is detected without the need for expensive instruments or specialized knowledge, the developed sensor is suitable for on-site workers in industries requiring the quick detection of gaseous ammonia at concentration levels above those considered acceptable by the Occupational Safety and Health Administration (OSHA). The sensor's ease of use and repeatability lower manufacturing and detection costs, making it an economical choice for small businesses.
As significant levels of total volatile nitrogen compounds can be produced during the preparation, storage, and transportation of such foods, the researchers believe that the straightforward, quick, and affordable process they developed for creating the colorimetric ammonia sensor can be further extended to the food packaging sector, particularly for meat and fish.
Sangwon Lee, Eun‐Hee Lee and Seung‐Woo Lee (2022) A Flexible and Attachable Colorimetric Film Sensor for the Detection of Gaseous Ammonia. Biosensors. https://www.mdpi.com/2079-6374/12/8/664