The Optical Nose: Monolayer Sensitisation of Au Surfaces for Plasmonic Gas Sensing

Robust real-time gas sensing is important for many fields, including agriculture and healthcare analysis of breath/biofluid volatiles. Ammonia is ambiently present at ppb to ppm levels, but current detection technologies suffer long measurement times, instability, cost, and issues with selectivity. Here, surface-enhanced Raman spectroscopy (SERS) is dramatically improved through precision precleaning protocols which allow surface-sensitization of the metal facets using a water monolayer. Harnessing monolayer aggregates of densely-packed gold nanoparticles with sub-nm spacing defined by rigid scaffolding molecules, gives sub-ppm detection of ammonia at room temperature. Accessing the poorly-studied high-wavenumber (>2500 cm-1) region provides much improved discriminatory capabilities, enabling us to generalise this approach to a range of volatile organic carbon (VOC) molecules including ethanol, methanol, and acetone.