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 at TMOS, the Australian Research Council’s Center of Excellence for Transformative Meta-Optical Systems, have developed a sensor made from an array of nanowires one-fifth of a square millimeter on each side, meaning it can easily be embedded in a silicon chip. .

In a study published in the latest issue Advanced materials, Ph.D. The sensor does not require a power source because it runs on its own solar-powered generator, explains Shiyu Wei, the center’s Australian National University team scientist and lead author.

Wei says: “As we integrate such devices into a sensor network for Internet of Things technology, low power consumption is a huge advantage in terms of system size and cost. The sensor can be installed in your car with an alarm and notifications sent to your phone if it detects dangerous levels of nitrogen dioxide emissions.”

Co-author Dr. Zhe Li says: “This device is just the beginning. It can also be adapted to detect other gases, such as acetone, which can be used as a non-invasive breath test for ketosis, including diabetic ketosis, which can: save 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 used a USB interface to connect to a computer.

Nitrogen dioxide is one of the NOx pollutant category. A contributor to acid rain, it is dangerous to humans even in small concentrations. It is a common pollutant from cars and is also created by indoor gas stoves.

The key to the device is the PN junction, the driver of the solar cell, which is in the form of a nanowire (a small hexagonal pillar about 100 nanometers in diameter, 3 to 4 µm high) that sits on the substrate. An ordered array of thousands of nanowire solar cells, spaced about 600 nanometers apart, formed the sensor.

The entire device was made of indium phosphide with zinc as the base to form the P portion and the N portion at the tip of the nanowires with silicon. The middle part of each nanowire was untreated (inner part, I), separating the P and N parts.

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 touches any nitrogen dioxide, which is a strong oxidizing agent that absorbs electrons, it will cause the current to drop.

The dip size allows you to calculate the concentration of nitrogen dioxide in the air. Numerical modeling by EME postdoctoral fellow Dr. Zhe Li has shown that the design and fabrication of the PN junction is critical to maximizing signal.

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

TMOS Principal Investigator, Research Group Leader Professor Lan Fu says: “The ultimate goal is to sense multiple gases on one tiny chip. As well as environmental pollutants, these sensors can be used for healthcare, such as breath tests for biomarkers. disease.

“The tiny gas sensor is easily integrable and scalable. This, combined with meta-optics, promises to achieve multiplexing sensors with high performance and multiple functions, allowing them to fit into smart sensing networks. TMOS is a network of research groups across the region. Australia is committed to advancing this industry.

“The technologies we develop will change our lives and society in the coming years, with large-scale implementation of Internet of Things technology in real-time data collection and autonomous response applications such as air pollution monitoring, industrial chemical hazard detection, smart cities. , and maintenance of personal health.