Multiplex volatile organic compound Raman sensing with nanophotonic slot waveguides functionalized with a mesoporous enrichment layer

We report, to the best of our knowledge, the first Raman sensor for broadband vapor-phase volatile organic compounds (VOCs) based on silicon nitride waveguides functionalized with a mesoporous silica top-cladding. The Raman response of low-concentration VOC gases is evanescently probed via a centimeter-long functionalized slot waveguide. Thanks to the four-orders-of-magnitude concentration factor offered by the mesoporous coating, the detection limit of acetone, ethanol, and isopropyl alcohol (IPA) is determined to be 594, 157, and 53 ppm, respectively, with 1 s measurement time in the current setup. Capable of multiplex gas sensing in a complex matrix through fast and reversible adsorption, the demonstration paves the way to on-site continuous VOC monitoring.