Gas leak checks are usually performed with a handheld instrument. Now, scientists at the Indian Institute of Sciences, Bangalore, are developing an “electronic nose” for this task, using nanomaterials.
S Venugopal, associate professor in the department of chemical engineering at IISc, is working with ISRO to develop hydrogen gas sensors using nanopalladium.
Nanomaterials have a large surface area, which is useful: gas molecules must interact with the sensor, so the larger the area, the greater the interaction. Nanomaterials with a large “interfacial area” are good at sniffing out gases.
At the nanoscale, palladium collects hydrogen to form palladium hydride, which swells it. “This increase in volume causes them to forge new electrical connections with neighboring particles, which translates into a decrease in resistance,” says an article on the subject in Core, The internal magazine of IISc. The change in resistance causes a corresponding change in electrical current, which can be measured.
But aren’t there gas sensors already in use? Venugopal said Quantum that different sensors are needed for different gases.
In addition, the use of nanoparticles is novel and these sensors can be placed where there is a danger of leaks, rather than exploring manually with a handheld instrument.
Venugopal said that while his lab is developing the nano palladium sensors for ISRO, they could also be used in other hydrogenated areas, such as fuel cells.
Meanwhile, another scientist, Navakanta Bhat, a professor at the Center for Nano Science and Engineering, IISc, is also developing sensors to detect as many odors as a human nose can. Its sensors use the chemical reactions of nanomaterials to detect a change in electrical resistance.
Some nanomaterials, such as metal oxides, undergo oxidation-reduction reactions when they come into contact with gases. Each metal oxide has an affinity for a particular gas.
Bhat’s team has developed a sensor array, consisting of different metal oxides, so that a single device can detect many gases.
However, another team, led by Abha Misra, associate professor in the department of instrumentation and applied physics, IISc, is working on sensors that can “remember” odors.
The Core The article quotes Misra as saying: “Gases are generally detected by virtue of electrons or charges that exchange with the detection material; if these charges can be trapped and retained, then a molecular memory can be created. “These sensors consist of a nanofilm (a few layers) of molybdenum disulfide and a semiconductor, along with a layer of graphene.
The ultimate goal of scientists is to develop a real enough electronic nose. A human nose has about six million sensors that can detect a trillion different smells.
A device with six million sensors is not possible, but AI can help here. Bhat students are exploring the use of AI in sensor arrays.
Gas sensors can also be extremely useful in healthcare: every breath we take lets out thousands of organic molecules, and their identification can aid in the diagnosis of disease.