A team of researchers from the Indian Institute of Science have developed a novel sensor to detect nitrogen dioxide (NO2) in the atmosphere. The sensor, which can catch a single nitrogen dioxide molecule among millions of other molecules, is one of the most sensitive in the world. Also, unlike other NO2 sensors which perform at high temperatures, the new sensor works even at room temperature.
NO2 is a harmful gas mostly emitted by diesel engines and thermal power plants. It can react with air and cause acid rain, and can also reduce the amount of oxygen in marine ecosystems. If it's concentration in air crosses a limit, it could be harmful for humans too. Obviously, detecting this gas is an important first step towards dealing with environmental air and water pollution caused by it.
The IISc team covered what is called a Fibre Bragg Grating with an ultrathin layer of a recently discovered 'nanomaterial' called Reduced Graphene Oxide, to develop the novel sensor. A Fibre Bragg Grating is an optical fibre (something like the optical fibre cables that make our internet connections feasible) which can reflect one particular wavelength of light and transmit others.
“An Optical Fiber is usually used for communication purposes, but by ingeniously modifying the clad of an optical fibre, we are able to use it in different applications like gas sensing and biosensing”, explains Sundarrajan Asokan, a Professor at the Department of Instrumentation and Applied Physics and the Robert Bosch Centre for Cyber Physical Systems, one of the authors of the paper.
In the presence of NO2, the Bragg wavelength reflected by the fiber Bragg grating changes due to the adsorption of gas molecules on the surface of the reduced graphene oxide. By measuring this change in the reflected wavelength, the amount of NO2 in the atmosphere can be detected.
Although the same research team and others have used the combination of graphene oxide and Fibre Bragg gratings for several biochemical sensing applications previously, this is the first time the two technologies have been combined to make an effective NO2 sensor. It is not only sensitive, but also has the ability to pick only NO2 molecules from a mixture of different gases. Since the sensor works at room temperature, it is easier to use in real world situations compared to other NO2 sensors where high working temperatures are required.
The process used to fabricate the sensor can also be scaled up which can potentially reduce the cost of the sensor. According to Prof. Ajay Sood, Professor at the Department of Physics, co-author of the work one of the authors, “Every process involved in fabricating the sensor, from manufacturing the etched fibre Bragg grating to coating it with reduced graphene oxide, are scalable processes, which makes it easier to implement in large area sensors”.
The adverse effects of NO2 in the atmosphere are well understood and the sources of the gas also have been studied extensively. Now, with the help of extremely sensitive sensors, we can finally move on to detect the gas and possibly take effective measures to decrease the amount of this hazardous gas in the atmosphere thus protecting the environment and life.
About the authors:
Prof. Ajay Sood is a Professor at the Department of Physics, IISc. Contact: email@example.com
Prof. Sundarrajan Asokan is a Professor at Instrumentation and Applied Physics and Robert Bosch Centre for Cyber Physical Systems, IISc. Contact: firstname.lastname@example.org
Sridevi S is a Ph.D student jointly with Prof. S Asokan and Prof Sood,
Dr. K. S. Vasu, Ph D student of Prof Sood, is currently working as a post-doctoral research associate at The University of Manchester.