New nanowire sensors are the next step in the Internet of Things

A new tiny nitrogen dioxide sensor could help protect the environment from car pollutants that cause lung disease and acid rain.

Researchers from TMOS, the Australian Research Council Center of Excellence for Transformative Meta-Optical Systems, have developed a sensor with nanowires one-fifth of a square millimeter on each side, which means it can easily be embedded on a silicon chip. .

In a study published in the latest issue Advanced MaterialsPh.D., the Center’s Australian National University team scientist and lead author Shiyu Wei describes that the sensor does not need a power source because it runs on its own solar-powered generator.

Wei says: “Because we integrate such devices into a sensor network for Internet of Things technology, the low power consumption is a huge benefit in terms of system size and cost. The sensor can be installed in your car with an alarm. If it detects dangerous levels of nitrogen dioxide from the exhaust, an alert is sent to your phone. “

Lead author Dr. Zhe Li says: “This device is just the beginning. It can also be adapted to detect other gases, such as acetone. It can be used as a non-invasive breath test for ketosis, including diabetic ketosis, saving countless lives.

Existing gas detectors are bulky and slow and require a trained operator. In contrast, the new device can quickly and easily measure less than 1 part per billion, and the TMOS prototype uses a USB interface to connect to a computer.

Nitrogen dioxide is one of the NOx category of pollutants. In addition to contributing to acid rain, it is dangerous to humans even in small concentrations. It is a common pollutant in automobiles and is also produced indoors by gas stoves.

The key to the device is a PN junction in the form of a nanowire (a small hexagonal column with a diameter of about 100 nanometers and a height of 3-4 microns) sitting on the base – the engine of the solar cell. It created an ordered array of sensors made up of thousands of nanowire solar cells spaced about 600 nanometers apart.

The entire device is made of indium phosphide, the base is doped with zinc to form the P portion, and the N portion at the end of the nanowires is doped with silicon. The middle part of each nanowire was attached, separating the P and N parts (inset, I).

Light falling on the device causes a small current to flow between the N and P sections. However, if the inner middle of the PN junction is touched by any nitrogen dioxide, which is a strong oxidizing agent that absorbs electrons, this will cause the current to drop.

The dip measurement allows you to calculate the concentration of nitrogen dioxide in the air. Numerical modeling by Dr. Zhe Li, a postdoctoral researcher at EME, showed that the design and fabrication of the PN junction is critical to maximizing the signal.

The properties of nitrogen dioxide – strong adsorption, strong oxidation – make it easy to distinguish indium phosphide from other gases. The sensor can also be optimized to detect other gases by functionalizing the indium phosphide nanowire surface.

“The main goal is to sense many gases on one small chip. These sensors can be used not only for environmental pollutants, but also for healthcare, for example, for breath tests for biomarkers of disease,” says Professor Lan Fu, principal investigator of TMOS, head of the research group.

“The small gas sensor is easily integrable and scalable. It promises to achieve high-performance and multifunctional multiplexing sensors in combination with meta-optics, which will allow them to be adapted to smart sensing networks. TMOS is a network of research groups in various fields. Australia is dedicated to developing this field.

“The technologies we have developed will transform our lives and society in the coming years with the large-scale application of Internet of Things technology for autonomous response in applications such as real-time data collection and monitoring of air pollution, detection of industrial chemical hazards, smart cities, and personal health.”