Checks for gas leaks are usually made using a handheld instrument. Now, scientists at the Indian Institute of Science, Bangalore, are developing an ‘electronic nose’ for this task, using nanomaterials.
S Venugopal, associate professor at the department of chemical engineering in IISc, is working with ISRO to develop hydrogen gas sensors using nano palladium.
Nanomaterials have a large surface area, which is useful — the gas molecules need to interact with the sensor, so the larger the area, the more the interaction. Nanomaterials with a large ‘interfacial area’ are good for sniffing out gases.
At the nanoscale, palladium picks up hydrogen to form palladium hydride, which makes it swell. “This increase in volume makes them forge new electrical connections with neighbouring particles, resulting in decrease in resistance,” notes an article on the subject in Kernel , IISc’s in-house magazine. The change in resistance causes a corresponding change in electric current, which can be measured.
But aren’t there gas sensors already in use? Venugopal told Quantum that different sensors are needed for different gases.
Also, the use of nano particles is novel and these sensors can be placed wherever there is a danger of leaks, rather than scouting manually using a handheld instrument.
Venugopal said that while his lab is developing the nano palladium sensors for ISRO, they could also be used in other hydrogenous areas, such as fuel cells.
Meanwhile, another scientist, Navakanta Bhat, professor at the Centre for Nano Science and Engineering, IISc, is also developing sensors to detect as many odours as a human nose can. His sensors make use of the chemical reactions in the nanomaterials to detect a change in electrical resistance.
Some nanomaterials, such as those of metal oxides, undergo oxidation-reduction reactions when they come in contact with gases. Each metal oxide has an affinity to 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.
Yet another team — led by Abha Misra, associate professor at the department of instrumentation and applied physics, IISc — is working on sensors that can ‘remember’ smells.
The Kernel article quotes Misra as saying: “Gases are generally detected by virtue of electrons or charges they exchange with the sensing 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 disulphide and a semiconductor, along with a layer of graphene.
The ultimate aim of scientists is to develop a real enough electronic nose. A human nose has some 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’s students are exploring the use of AI in sensor arrays.
Sensors for gases can be extremely useful in healthcare, too — every breath of ours lets out thousands of organic molecules, and their identification can help in disease diagnosis.