Photoluminescence-based gas sensing with MoS₂ monolayers

Two-dimensional transition metal dichalcogenides (TMDs) are highly appealing for gas sensors, lab-on-a-chip devices, and biosensing applications because of their strong light-matter interaction and high surface-to-volume ratio. The ability to grow these van der Waals materials on different substrates and waveguide geometries opens a horizon toward scalable on-chip photonic nanodevices. Here we report on a versatile technique for remote optical gas sensing using two-dimensional TMDs. The adsorption of the gas molecules on the monolayer surface provides a gateway for gas sensing based on charge-transfer-induced photoluminescence variation. For gases that are weakly adsorbed on the surface of monolayer TMDs, purging the monolayers' surface by an inert gas like N₂ can desorb gases from the monolayers at room temperature. We demonstrate CO, NO, and NO₂ detection by monitoring photoluminescence from semiconducting MoS₂ monolayers grown on SiO₂/Si chips at a level of 10 ppm with fast response time. Observations are supported by our density functional theory calculations, which predict a significant interaction between these gases and MoS₂ monolayers. These findings may lead to advances in remote sensing, surface-sensitive bioanalytics, and lab-on-a-chip sensors.