How cool would it be to have a mobile phone equipped with a pollution sensor? This could one day become a reality with researchers at the Indian Institute of Science (IISc.) developing a highly sensitive low-cost sensor to detect carbon monoxide levels, small enough to fit into a mobile phone.
While conventional sensors are made through lithography (similar to printing circuits but at nano scale), the team used a low-cost fabrication technique of pouring semiconductor material over nano beads to build a honeycomb-like nano-structure made up of zinc oxide.
The research was carried out by Chandra Shekhar Prajapati, post-doctoral fellow, and Navakanta Bhat, Chair & Professor, Centre for Nano Science and Engineering (CeNSE), IISc., along with researchers at the KTH Royal Institute of Technology, Sweden. The study was published in peer-reviewed Sensors and Actuators B: Chemical in June 2017.
So how does this technique improve sensitivity of the device? A simple way to explain this, says Dr. Prajapati, is to imagine a group of really small hexagonal polystyrene beads arranged in a pattern over the sensing material and more of the same material deposited in the gaps to form a honeycomb pattern.
The sensor can quickly detect minute changes in carbon monoxide levels, and can be used in environmental pollution monitoring. "Imagine the difference between a flat surface and a dimpled one. The second would be more sensitive, as there would be greater surface area to interact with gases," explains Dr. Bhat.
The same technique can be extended to develop other gas sensors as well. "It can be used for other oxides and even metals can be structured in this technique. Palladium and platinum are good for hydrogen sensors," says Dr. Prajapati.
Conventional optical sensors are much bulkier, measuring at least a few centimetres across, while the sensor devised is less than 1 mm. And while nano sensors are not new, the uniqueness of the research lies in the low cost technique and high sensitivity of the sensors. The scientists developed sensors with varying widths of the honeycomb pattern and the one with the smallest width (~100 nm) was able to detect a change of even 500 parts per billion in CO concentration.
This sensitivity could be vital in mines where early detection of carbon monoxide could save lives. "It can also be used to detect CO levels at traffic junctions," said Prof Bhat, adding, "The holy grail that scientists are aiming for is fitting these sensors in mobile phones."
