doi:10.1038/nindia.2013.35 Published online 12 March 2013
Researchers have invented a novel, fast and ultrasensitive magnetic-nanofluid-based optical sensor that changes colour on exposure to extremely low concentrations of ammonia1 . The sensor will be useful in detecting minute traces of ammonia in industrial and environmental samples.
Ammonia is an important ingredient in explosives, fertilizers and industrial coolants. However, high concentrations of ammonia gas are harmful to humans and other living organisms. Existing techniques for monitoring ammonia levels in industrial and environmental samples are expensive, complex and time-consuming.
To design a portable and fast detection technique, the researchers synthesized a magnetic nanofluid by dispersing ferrimagnetic iron oxide nanoparticles in a mixture of oil, water and surfactant. This nanofluid consists of nanodroplets suspended in water.
They then placed the magnetic nanofluid in a vial, which was put inside a solenoid coil connected to a current supply. At a fixed magnetic field, a fibre-optic light source illuminated the nanofluid to which varying concentrations of ammonia were gradually added.
The colour of the nanofluid changes depending on the ammonia concentration. This color change occurs within a second after exposure to ammonia, much faster than other ammonia-sensing methods that could take several minutes. "The sensor shows a fast response because the nanodroplets in the nanofluid are suspended in water," says lead researcher John Philip. In the future, this sensor could also be used to detect other toxic ions and gases, he adds.