The technique presents the fabrication of ultrasensitive resistive gas sensing chips based on a metal oxide nanocomposite and the construction of a portable cloud access environmental nitrogen dioxide gas sensor. The sensor is wirelessly connected to a cell phone via the bluetooth circuit. The resistance change is recorded in an APP program and the NO2 concentration in the surrounding environment can be obtained. The measured data can be uploaded to a cloud data base. The NO2 detection range is between 5 and 1000 ppb with a resolution of 5 ppb. The sensor functions normally in a high temperature and high humidity environment and is suitable for environmental air quality monitoring. The cloud access gas sensor is currently under field test in an Environmental Protection Administration air quality monitoring station for side by side comparison. Several units have been installed in New Taipei City for field evaluation.

We fabricate a ternary nanocomposite made of Au nanoparticles, CuxO nanoparticles and ZnO nanorods for chemiresistive low concentration gas sensing. The gas sensing chips can be batch-produced on a 4 inch Si wafer. Under ambient environment, a response of around 5% at 5 ppb NO2 can be obtained, which sensitivity is suitable for environmental monitoring of NO2.  After field test verification in a period of 2 months, the nanocomposite shows high stability and can be used in a high temperature and high humidity environment. With such remarkable performance, the nanocomposite has excellent prospect for commercialization.

The portable gas sensor can be used in the air pollution prevention industry and the manufacturing process monitoring industry. The nanocomposite growth technique can be used in the photocatalytic antibacterial industry. The environmental gas concentration data analysis technique can be used in the big data analysis industry.