Real-time detection of trace analytes using molecular-antenna-enhanced photothermal spectroscopy

Chemical sensing of vapor-phase analytes using photothermal spectroscopy of adsorbed molecules on microfabricated devices shows high selectivity. However, because of the small surface area of microfabricated sensors, the areal density of the adsorbate can dip below detection limits when the ambient analyte concentration is low. These sensors can benefit from being fed higher concentrations of target analytes for real-time sensing. However, the use of pre-concentrators to increase the ambient concentration of analyte molecules normally results in longer detection times. In this work, we present a real-time pre-concentrator for photothermal spectroscopy by spatially separating the sensor area from the molecular adsorption area. We demonstrate this technique by detecting perfluorooctanoic acid (PFOA) and dimethyl methylphosphonate (DMMP) molecules, with a limit of detection (LOD) in the pg/cm² range, an enhancement of three orders of magnitude over other methods.