Nanoplasmonic NO2 Sensor with a Sub-10 Parts per Billion Limit of Detection in Urban Air

Urban air pollution is a critical health problem in cities all around the world. Therefore, spatially highly resolved real-time monitoring of airborne pollutants, in general, and of nitrogen dioxide, NO2, in particular, is of utmost importance. However, highly accurate butfixed and bulkymeasurement stations or satellites are used for this purpose to date. This defines a need for miniaturized NO2sensor solutions with detection limits in the low parts per billion range to finally enable indicative air quality monitoring at low cost that facilitates detection of highly local emission peaksand enables the implementation of direct local actions like traffic control, toimmediately reduce local emissions. To address this challenge, we present ananoplasmonic NO2sensor based on arrays of Au nanoparticles coated with a thin layer of polycrystalline WO3, which displays aspectral redshift in the localized surface plasmon resonance in response to NO2. Sensor performance is characterized under (i)idealized laboratory conditions, (ii) conditions simulating humid urban air, and (iii) an outdoorfield test in a miniaturized devicebenchmarked against a commercial NO2sensor approved according to European and American standards. The limit of detection ofthe plasmonic solution is below 10 ppb in all conditions. The observed plasmonic response is attributed to a combination of chargetransfer between the WO3layer and the plasmonic Au nanoparticles, WO3layer volume expansion, and changes in WO3permittivity.The obtained results highlight the viability of nanoplasmonic gas sensors, in general, and their potential for practical application in indicative urban air monitoring, in particular

Automated summary

Urban air pollution is a critical health problem worldwide. To enable indicative air quality monitoring at low cost and reduce local emissions, miniaturized NO2sensor solutions are needed. This study presents a nanoplasmonic NO2sensor based on gold nanoparticles coated with a thin layer of polycrystalline WO3, which shows a spectral redshift in response to NO2. The sensor's performance was evaluated under various conditions and compared with a commercial NO2sensor. The results demonstrate the feasibility and potential of nanoplasmonic gas sensors for indicative urban air monitoring.