An optimised gas sensor microsystem for accurate and real-time measurement of nitrogen dioxide at ppb level

The efficient monitoring of nitrogen dioxide (NO2) at concentrations commonly measurable in urban atmosphere (from few ppb to 100 ppb) by an original gas sensor microsystem is presented in this paper. The reproducibility, resolution, threshold and selectivity are criteria especially quantified and discussed. The sensitive element is a mere chemiresistor based on a thin layer of copper phthalocyanine (CuPc), a skilled molecular material, well known to be strongly sensitive towards oxidising species such as NO2. The implementation of a judicious methodology of measurements, founded on the exploitation of the sensor response kinetics at low temperatures, allows the NO2 monitoring to be optimised. By means of such a methodology, sensor drawbacks such as long response time and drift are avoided. As a result, the sensing performances are certainly improved. The optimum experimental parameters, namely sampling period, temperatures and exposure time/regeneration time ratio are argued and justified experimentally. Measurements under well-controlled and artificially NO2-polluted atmosphere illustrate the best performances obtained. As a consequence, the measurements are reproducible with a very low detection threshold (10 ppb) and a high resolution is accomplished (<20 ppb). Moreover, the concentration level is accessible in real time. Finally, the selectivity of this microsystem towards NO2 using an all-organic sensor/filter integrated device is also discussed.