Optical Sensing of Strong Electron Donor Vapors Using Monolayer WS₂

We report the sensing by the partial quenching of the photoluminescence (PL) response of monolayer WS₂ to the vapor of the strong electron donor tripropylamine (TPA) in the parts per billion (ppb) concentration range. The PL response at 3 ppb, the lowest vapor concentration available with our dosing system, is consistently repeatable. This, together with the large signal-to-noise ratio of the response at 3 ppb, suggests that optical detection by WS₂ monolayers should be able to sense similar vapors well below 1 ppb. We show more generally that WS₂ monolayers are selectively sensitive only to strong electron donors, and are remarkably insensitive to water vapor and other common atmospheric constituents, thus drastically reducing the potential for false positive detection of common ambient vapors. Strong electron donors represent a wide class of compounds, many of which are highly toxic and some are of national defense/military concern. The ability to detect these vapors rapidly and selectively in the ppb range would provide a first alert of their presence, as no strong electron donor vapors should be present in ambient air even in ppb concentrations. We envision arrays of sensitive and selective monolayer WS2 vapor sensors to provide real-time air monitoring for public safety.